F-150 brakes

On 06/06/2011 11:44 AM, Pete C. wrote:
>
> jim beam wrote:
>>
>> On 06/06/2011 10:25 AM, Pete C. wrote:
>>>
>>> jim beam wrote:
>>>>
>>>> On 06/06/2011 08:20 AM, C. E. White wrote:
>>>>> > wrote in message
>>>>> ...
>>>>>>
>>>>>> "C. E. > wrote in message
>>>>>> ...
>>>>>>>
>>>>>>> "jim > wrote in message
>>>>>>> t...
>>>>>>>> On 06/04/2011 08:56 PM, Pete C. wrote:
>>>>>>>>>
>>>>>>>>> Ashton Crusher wrote:
>>>>>>>>>>
>>>>>>>>>> On Tue, 31 May 2011 09:22:08 -0500, "Pete >
>>>>>>>>>> wrote:
>>>>>>>>>>
>>>>>>>>>>>
>>>>>>>>>>> "C. E. White" wrote:
>>>>>>>>>>>>
>>>>>>>>>>>> "Pete > wrote in message
>>>>>>>>>>>> ter.com...
>>>>>>>>>>>>>
>>>>>>>>>>>>> Tom Del Rosso wrote:
>>>>>>>>>>>>>>
>>>>>>>>>>>>>> On Top Gear, Jeremy said the F-150 is a POS. One key point was
>>>>>>>>>>>>>> his claim
>>>>>>>>>>>>>> that the brake pads are "the size of bottle caps" and are
>>>>>>>>>>>>>> inadequate for
>>>>>>>>>>>>>> a
>>>>>>>>>>>>>> vehicle of this weight and power. Is that a real issue or one
>>>>>>>>>>>>>> man's
>>>>>>>>>>>>>> opinion?
>>>>>>>>>>>>
>>>>>>>>>>>> I love Top Gear, but as others have noted Clarkson seems to hate
>>>>>>>>>>>> most
>>>>>>>>>>>> American vehicles (or at least pretends to - not sure when he is
>>>>>>>>>>>> catering to
>>>>>>>>>>>> the audience and when he is sincere). But then he especially hates
>>>>>>>>>>>> the
>>>>>>>>>>>> Prius, so he can't be all bad.
>>>>>>>>>>>>
>>>>>>>>>>>>> I don't have an F150, but based on the brake complaints from
>>>>>>>>>>>>> several
>>>>>>>>>>>>> friends who do, and their comments on how much better my F350
>>>>>>>>>>>>> brakes
>>>>>>>>>>>>> are, I'd say that the F150 brakes are inadequate.
>>>>>>>>>>>>
>>>>>>>>>>>> I have a 2009 F150. The brakes take some getting used to compared to
>>>>>>>>>>>> my old
>>>>>>>>>>>> Frontier. In my opinion. it is not the pad size, or rotor size, or
>>>>>>>>>>>> the
>>>>>>>>>>>> ultimate braking ability that is an issue. It is the boost
>>>>>>>>>>>> characteristics
>>>>>>>>>>>> and the way the suspension reacts to braking that are generating
>>>>>>>>>>>> complaints.
>>>>>>>>>>>> The brake boost seems "soft" by comparison with my previous truck
>>>>>>>>>>>> (an '06
>>>>>>>>>>>> Frontier). By that I mean the brakes feel soft - unless you really
>>>>>>>>>>>> do want
>>>>>>>>>>>> to do a hard stop. Plus the truck seems to have a lot of "anti-dive"
>>>>>>>>>>>> built
>>>>>>>>>>>> into the front suspension. By this I mean when you really stand on
>>>>>>>>>>>> the
>>>>>>>>>>>> brakes, the front end doesn't dip down like some vehicles. This
>>>>>>>>>>>> makes it
>>>>>>>>>>>> seem as if the brakes aren't working as well as in some vehicles
>>>>>>>>>>>> where the
>>>>>>>>>>>> front end drops sharply under braking. I occasionally drive a
>>>>>>>>>>>> neighboor
>>>>>>>>>>>> Silverado HD and his brakes seem to haul you down sharply with a
>>>>>>>>>>>> relatively
>>>>>>>>>>>> light touch on the pedals (sort of like some of the old Chrsyler
>>>>>>>>>>>> Products
>>>>>>>>>>>> that would almost throw you through the windshield if you touched
>>>>>>>>>>>> the
>>>>>>>>>>>> brakes). This makes them seem a lot more powerful, but without any
>>>>>>>>>>>> sort of
>>>>>>>>>>>> actual measurements, is it really true? One thing for sure, the
>>>>>>>>>>>> anti-lock
>>>>>>>>>>>> activation of my F150 is far better than it was in the Frontier. The
>>>>>>>>>>>> ABS in
>>>>>>>>>>>> my '06 Frontier kicked in often on almost any surface but a paved
>>>>>>>>>>>> road. It
>>>>>>>>>>>> was pretty un-nerving at times.
>>>>>>>>>>>>
>>>>>>>>>>>> For comaprison, I took a look at the Consumer Reports Tests for 1/2
>>>>>>>>>>>> Ton Crew
>>>>>>>>>>>> Cab Pick-ups:
>>>>>>>>>>>> Braking Distance
>>>>>>>>>>>> from 60 (ft)
>>>>>>>>>>>> Vehicle Dry Wet
>>>>>>>>>>>> 2009 F150 XLT V8 138 150
>>>>>>>>>>>> 2009 Chevrolet Silverado 150 163
>>>>>>>>>>>> 2007 Toyota Tundra 153 178
>>>>>>>>>>>> 2009 Dodge Ram 137 155
>>>>>>>>>>>> 2004 Nissan Titan 139 154
>>>>>>>>>>>> 2002 F150 XLT 151 --- (older test)
>>>>>>>>>>>>
>>>>>>>>>>>> If you trust CR (hard to do I know) it seems that the F150 Brakes
>>>>>>>>>>>> are as
>>>>>>>>>>>> good as anyones. The 2009 F150 in the CR test had 20 inch wheels
>>>>>>>>>>>> with
>>>>>>>>>>>> Pirelli Scorpion Tires. I suspect these tires had a lot better
>>>>>>>>>>>> braking
>>>>>>>>>>>> performance than the 18 inch General Tires that came on my 2009
>>>>>>>>>>>> F150. Too
>>>>>>>>>>>> bad they don't have a comparison of the same truck with different
>>>>>>>>>>>> tire
>>>>>>>>>>>> options installed. My truck seems better on the Bridgestones I
>>>>>>>>>>>> installed
>>>>>>>>>>>> last year. It might just be in my mind, but I am sure I have better
>>>>>>>>>>>> off road
>>>>>>>>>>>> traction.
>>>>>>>>>>>>
>>>>>>>>>>>> Ed
>>>>>>>>>>>
>>>>>>>>>>> I expect those numbers are for empty trucks. At least one of my
>>>>>>>>>>> friends
>>>>>>>>>>> tows trailers that are heavy but within the rated spec for his F150
>>>>>>>>>>> (with WD hitch), and he reports that the brakes truly are inadequate
>>>>>>>>>>> with a load.
>>>>>>>>>>
>>>>>>>>>> What's wrong with the trailers brakes???
>>>>>>>>>
>>>>>>>>> I couldn't tell you, the times I've been around when he's been towing a
>>>>>>>>> heavy trailer we haven't had time to experiment with WD hitch settings
>>>>>>>>> and whatnot. Putting the same trailer behind my F350 it's not even
>>>>>>>>> noticeable.
>>>>>>>>
>>>>>>>> it was an uninformed/smoke screen question - many trailers don't have
>>>>>>>> brakes at all.
>>>>>>>
>>>>>>> Not a problem for relatively light trailers. But if you towing anything
>>>>>>> close to then maximum tow capacity you need trailer brakes.
>>>>>>>
>>>>>>>> getting back to the point, any vehicle with a cargo bed should be able
>>>>>>>> to stop a load. on a hill. more than once. whether that load is on
>>>>>>>> the bed or following behind is irrelevant.
>>>>>>>
>>>>>>> Not irrelevant. A load in the bed increases the tire traction available
>>>>>>> for braking. The same load on a trailer without trialer brakes doesn't
>>>>>>> load the tow vehicle tires nearly as much (maybe 20% as much if you have
>>>>>>> the tongue weight right). Therfore, you have less tire traction available
>>>>>>> to stop the combination. If you don't have anti-lock brakes, then you can
>>>>>>> easily lock the rear brakes on the tow vehicle when trying to stop the
>>>>>>> vehicle plus trailer (with the dire consequences that follow). If you do
>>>>>>> have antilock brakes, then you can't lock the rear wheels, but you also
>>>>>>> won't have as much braking force available (comparded to having the load
>>>>>>> in the bed). And then there is the whole problem with jack-knifing a
>>>>>>> trailer with no trialer brakes. Certainly stopping a vehicle with a
>>>>>>> trailer without trailer brakes is much different than stopping a vehicle
>>>>>>> with the load in the bed.
>>>>>>>
>>>>>>> I looked into brakes of the current F150 some more. It seems Ford claims
>>>>>>> they have a dual diaphram brake booster and electronic brake force
>>>>>>> distribution. Neither claim is made for the SuperDuties. Not sure of the
>>>>>>> implications. The biggest difference at the wheel end is that the
>>>>>>> SuperDuties have dual piston rear calipers, the F150's have single piston
>>>>>>> rear calipers. Brake disc sizes are similar, total swept area is similar.
>>>>>>> I really don't see any reason to think that the F150 brakes are
>>>>>>> inadequate if you tow trailers that don't exceed the rated GCVW.
>>>>>>>
>>>>>>> Ed
>>>>>>
>>>>>> Assuming both rotors have the same swept area, and that
>>>>>> the pads are of the same size and material, would you
>>>>>> expect the addition of a second piston alone to have a
>>>>>> major effect on the stopping power? Pressure applied
>>>>>> to the pads should be the same whether you use one or
>>>>>> two pistons. You dont double the pressure when you
>>>>>> apply pressure to both sides, versus deadheading the
>>>>>> same pressure on one side only.
>>>>>
>>>>> In this context, the dual pistons are on the same side of the caliper. The
>>>>> brakes are still sliding caliper types, just with two pistons side by side
>>>>> on one side of the caliper. I haven't found the actual piston sizes, but I
>>>>> assume the F250+ brakes can apply significantly more pressure on the rear
>>>>> pads than the F150 single piston calipers
>>>>>
>>>>> Ed
>>>>>
>>>>>
>>>>
>>>> you, of all people ed, shouldn't "assume" a damned thing.
>>>>
>>>> piston count does not "increase" pressure. it can improve braking
>>>> because mechanical elasticity becomes less of a concern, and thus you
>>>> can have a more effective brake for less weight [and money].
>>>
>>> Increasing the total piston area increases the applied force for a given
>>> brake line hydraulic pressure.
>>
>> absolutely, but absent ed's "actual piston sizes", we can't say that.
>
> Nope, but we can reasonably assume that the total piston area is larger
> on the Super Duty series calipers than on the F150 calipers.

there is no point in increasing the total piston areas. see below.


>
>>
>>> If for example the F150 calipers had a
>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
>>> the applied clamping force on the rotor would double given the same
>>> hydraulic pressure.
>>
>> if the master piston diameter stays the same. but because of the
>> leverage ratio, and the limited amount of brake pedal travel available,
>> ratios typically remain close. [given a long enough pedal travel, you
>> could dispense with brake boosters.]
>
> Larger brake boosters (or hydroboost) allow for larger master cylinder
> diameters increasing volume without increasing pedal travel.

- to keep the relative ratios fairly constant.

by definition, if the slave area doubles, the master must also double or
the pedal travel will double. the latter is clearly impracticable -
there is very little latitude to vary these ratios, and certainly not by
a factor of two.


>
>>
>>> The displacement and required fluid of course would
>>> also double.
>>>
>>>>
>>>> and as for "weight improving traction" [this is going to be a classic] -
>>>> why exactly does increasing weight increase stopping distance ed? go
>>>> on, give it a shot.
>>>
>>> The short answer is that increasing weight does not automatically
>>> increase stopping distance. There is something of a dip in the stopping
>>> distance where the stopping distance decreases as weight is added up to
>>> a point before the stopping distance begins to increase again as further
>>> weight is added.
>>>
>>> What happens is that an axle that is too lightly loaded (such as the
>>> rear in an unloaded pickup) is not able to apply the full available
>>> braking force without wheel lockup so that the effective braking
>>> capacity is limited by the lack of traction. As weight is added,
>>> traction improves allowing more brake force to be applied without
>>> lockup, resulting in shorter stopping distances. Once there is enough
>>> weigh to provide sufficient traction to match the maximum braking force
>>> available, that will be the shorted stopping distance in the graph.
>>> Additional weight past this point will again increase the stopping
>>> distance.
>>
>> that's a function of two things: tire contact area and control. if
>> tires are over-inflated relative to load, contact area is reduced.
>> that's introducing an additional variable rather than talking braking
>> physics. same for control - if it's too cheap or ineffective to not be
>> proportioning relative to weight, again, the solution is not to load
>> more weight, it's to exercise better control.
>
> It has nothing to do with control,

then, with respect, you don't understand what "control" means.


> it has everything to do with a light
> weight which provides insufficient traction weight on the axle to give
> the traction necessary to utilize the brakes full capacity.

that's adding weight to increase tire contact area, not braking capacity.


> Proportioning and ABS both work to limit the applied brake force to a
> level that the traction can support, in effect reducing the braking
> capacity.

they don't "decrease" braking capacity, they decrease skidding.
skidding isn't braking capacity.


> When added weight adds traction, more of the available braking
> force can be utilized.

KE = 1/2 M.V^2

if you add weight, you increase the amount of braking required.


--
nomina rutrum rutrum

jim beam wrote:
>
> On 06/06/2011 11:44 AM, Pete C. wrote:
> >
> > jim beam wrote:
> >>
> >> On 06/06/2011 10:25 AM, Pete C. wrote:
> >>>
> >>> jim beam wrote:
> >>>>
> >>>> On 06/06/2011 08:20 AM, C. E. White wrote:
> >>>>> > wrote in message
> >>>>> ...
> >>>>>>
> >>>>>> "C. E. > wrote in message
> >>>>>> ...
> >>>>>>>
> >>>>>>> "jim > wrote in message
> >>>>>>> t...
> >>>>>>>> On 06/04/2011 08:56 PM, Pete C. wrote:
> >>>>>>>>>
> >>>>>>>>> Ashton Crusher wrote:
> >>>>>>>>>>
> >>>>>>>>>> On Tue, 31 May 2011 09:22:08 -0500, "Pete >
> >>>>>>>>>> wrote:
> >>>>>>>>>>
> >>>>>>>>>>>
> >>>>>>>>>>> "C. E. White" wrote:
> >>>>>>>>>>>>
> >>>>>>>>>>>> "Pete > wrote in message
> >>>>>>>>>>>> ter.com...
> >>>>>>>>>>>>>
> >>>>>>>>>>>>> Tom Del Rosso wrote:
> >>>>>>>>>>>>>>
> >>>>>>>>>>>>>> On Top Gear, Jeremy said the F-150 is a POS. One key point was
> >>>>>>>>>>>>>> his claim
> >>>>>>>>>>>>>> that the brake pads are "the size of bottle caps" and are
> >>>>>>>>>>>>>> inadequate for
> >>>>>>>>>>>>>> a
> >>>>>>>>>>>>>> vehicle of this weight and power. Is that a real issue or one
> >>>>>>>>>>>>>> man's
> >>>>>>>>>>>>>> opinion?
> >>>>>>>>>>>>
> >>>>>>>>>>>> I love Top Gear, but as others have noted Clarkson seems to hate
> >>>>>>>>>>>> most
> >>>>>>>>>>>> American vehicles (or at least pretends to - not sure when he is
> >>>>>>>>>>>> catering to
> >>>>>>>>>>>> the audience and when he is sincere). But then he especially hates
> >>>>>>>>>>>> the
> >>>>>>>>>>>> Prius, so he can't be all bad.
> >>>>>>>>>>>>
> >>>>>>>>>>>>> I don't have an F150, but based on the brake complaints from
> >>>>>>>>>>>>> several
> >>>>>>>>>>>>> friends who do, and their comments on how much better my F350
> >>>>>>>>>>>>> brakes
> >>>>>>>>>>>>> are, I'd say that the F150 brakes are inadequate.
> >>>>>>>>>>>>
> >>>>>>>>>>>> I have a 2009 F150. The brakes take some getting used to compared to
> >>>>>>>>>>>> my old
> >>>>>>>>>>>> Frontier. In my opinion. it is not the pad size, or rotor size, or
> >>>>>>>>>>>> the
> >>>>>>>>>>>> ultimate braking ability that is an issue. It is the boost
> >>>>>>>>>>>> characteristics
> >>>>>>>>>>>> and the way the suspension reacts to braking that are generating
> >>>>>>>>>>>> complaints.
> >>>>>>>>>>>> The brake boost seems "soft" by comparison with my previous truck
> >>>>>>>>>>>> (an '06
> >>>>>>>>>>>> Frontier). By that I mean the brakes feel soft - unless you really
> >>>>>>>>>>>> do want
> >>>>>>>>>>>> to do a hard stop. Plus the truck seems to have a lot of "anti-dive"
> >>>>>>>>>>>> built
> >>>>>>>>>>>> into the front suspension. By this I mean when you really stand on
> >>>>>>>>>>>> the
> >>>>>>>>>>>> brakes, the front end doesn't dip down like some vehicles. This
> >>>>>>>>>>>> makes it
> >>>>>>>>>>>> seem as if the brakes aren't working as well as in some vehicles
> >>>>>>>>>>>> where the
> >>>>>>>>>>>> front end drops sharply under braking. I occasionally drive a
> >>>>>>>>>>>> neighboor
> >>>>>>>>>>>> Silverado HD and his brakes seem to haul you down sharply with a
> >>>>>>>>>>>> relatively
> >>>>>>>>>>>> light touch on the pedals (sort of like some of the old Chrsyler
> >>>>>>>>>>>> Products
> >>>>>>>>>>>> that would almost throw you through the windshield if you touched
> >>>>>>>>>>>> the
> >>>>>>>>>>>> brakes). This makes them seem a lot more powerful, but without any
> >>>>>>>>>>>> sort of
> >>>>>>>>>>>> actual measurements, is it really true? One thing for sure, the
> >>>>>>>>>>>> anti-lock
> >>>>>>>>>>>> activation of my F150 is far better than it was in the Frontier. The
> >>>>>>>>>>>> ABS in
> >>>>>>>>>>>> my '06 Frontier kicked in often on almost any surface but a paved
> >>>>>>>>>>>> road. It
> >>>>>>>>>>>> was pretty un-nerving at times.
> >>>>>>>>>>>>
> >>>>>>>>>>>> For comaprison, I took a look at the Consumer Reports Tests for 1/2
> >>>>>>>>>>>> Ton Crew
> >>>>>>>>>>>> Cab Pick-ups:
> >>>>>>>>>>>> Braking Distance
> >>>>>>>>>>>> from 60 (ft)
> >>>>>>>>>>>> Vehicle Dry Wet
> >>>>>>>>>>>> 2009 F150 XLT V8 138 150
> >>>>>>>>>>>> 2009 Chevrolet Silverado 150 163
> >>>>>>>>>>>> 2007 Toyota Tundra 153 178
> >>>>>>>>>>>> 2009 Dodge Ram 137 155
> >>>>>>>>>>>> 2004 Nissan Titan 139 154
> >>>>>>>>>>>> 2002 F150 XLT 151 --- (older test)
> >>>>>>>>>>>>
> >>>>>>>>>>>> If you trust CR (hard to do I know) it seems that the F150 Brakes
> >>>>>>>>>>>> are as
> >>>>>>>>>>>> good as anyones. The 2009 F150 in the CR test had 20 inch wheels
> >>>>>>>>>>>> with
> >>>>>>>>>>>> Pirelli Scorpion Tires. I suspect these tires had a lot better
> >>>>>>>>>>>> braking
> >>>>>>>>>>>> performance than the 18 inch General Tires that came on my 2009
> >>>>>>>>>>>> F150. Too
> >>>>>>>>>>>> bad they don't have a comparison of the same truck with different
> >>>>>>>>>>>> tire
> >>>>>>>>>>>> options installed. My truck seems better on the Bridgestones I
> >>>>>>>>>>>> installed
> >>>>>>>>>>>> last year. It might just be in my mind, but I am sure I have better
> >>>>>>>>>>>> off road
> >>>>>>>>>>>> traction.
> >>>>>>>>>>>>
> >>>>>>>>>>>> Ed
> >>>>>>>>>>>
> >>>>>>>>>>> I expect those numbers are for empty trucks. At least one of my
> >>>>>>>>>>> friends
> >>>>>>>>>>> tows trailers that are heavy but within the rated spec for his F150
> >>>>>>>>>>> (with WD hitch), and he reports that the brakes truly are inadequate
> >>>>>>>>>>> with a load.
> >>>>>>>>>>
> >>>>>>>>>> What's wrong with the trailers brakes???
> >>>>>>>>>
> >>>>>>>>> I couldn't tell you, the times I've been around when he's been towing a
> >>>>>>>>> heavy trailer we haven't had time to experiment with WD hitch settings
> >>>>>>>>> and whatnot. Putting the same trailer behind my F350 it's not even
> >>>>>>>>> noticeable.
> >>>>>>>>
> >>>>>>>> it was an uninformed/smoke screen question - many trailers don't have
> >>>>>>>> brakes at all.
> >>>>>>>
> >>>>>>> Not a problem for relatively light trailers. But if you towing anything
> >>>>>>> close to then maximum tow capacity you need trailer brakes.
> >>>>>>>
> >>>>>>>> getting back to the point, any vehicle with a cargo bed should be able
> >>>>>>>> to stop a load. on a hill. more than once. whether that load is on
> >>>>>>>> the bed or following behind is irrelevant.
> >>>>>>>
> >>>>>>> Not irrelevant. A load in the bed increases the tire traction available
> >>>>>>> for braking. The same load on a trailer without trialer brakes doesn't
> >>>>>>> load the tow vehicle tires nearly as much (maybe 20% as much if you have
> >>>>>>> the tongue weight right). Therfore, you have less tire traction available
> >>>>>>> to stop the combination. If you don't have anti-lock brakes, then you can
> >>>>>>> easily lock the rear brakes on the tow vehicle when trying to stop the
> >>>>>>> vehicle plus trailer (with the dire consequences that follow). If you do
> >>>>>>> have antilock brakes, then you can't lock the rear wheels, but you also
> >>>>>>> won't have as much braking force available (comparded to having the load
> >>>>>>> in the bed). And then there is the whole problem with jack-knifing a
> >>>>>>> trailer with no trialer brakes. Certainly stopping a vehicle with a
> >>>>>>> trailer without trailer brakes is much different than stopping a vehicle
> >>>>>>> with the load in the bed.
> >>>>>>>
> >>>>>>> I looked into brakes of the current F150 some more. It seems Ford claims
> >>>>>>> they have a dual diaphram brake booster and electronic brake force
> >>>>>>> distribution. Neither claim is made for the SuperDuties. Not sure of the
> >>>>>>> implications. The biggest difference at the wheel end is that the
> >>>>>>> SuperDuties have dual piston rear calipers, the F150's have single piston
> >>>>>>> rear calipers. Brake disc sizes are similar, total swept area is similar.
> >>>>>>> I really don't see any reason to think that the F150 brakes are
> >>>>>>> inadequate if you tow trailers that don't exceed the rated GCVW.
> >>>>>>>
> >>>>>>> Ed
> >>>>>>
> >>>>>> Assuming both rotors have the same swept area, and that
> >>>>>> the pads are of the same size and material, would you
> >>>>>> expect the addition of a second piston alone to have a
> >>>>>> major effect on the stopping power? Pressure applied
> >>>>>> to the pads should be the same whether you use one or
> >>>>>> two pistons. You dont double the pressure when you
> >>>>>> apply pressure to both sides, versus deadheading the
> >>>>>> same pressure on one side only.
> >>>>>
> >>>>> In this context, the dual pistons are on the same side of the caliper. The
> >>>>> brakes are still sliding caliper types, just with two pistons side by side
> >>>>> on one side of the caliper. I haven't found the actual piston sizes, but I
> >>>>> assume the F250+ brakes can apply significantly more pressure on the rear
> >>>>> pads than the F150 single piston calipers
> >>>>>
> >>>>> Ed
> >>>>>
> >>>>>
> >>>>
> >>>> you, of all people ed, shouldn't "assume" a damned thing.
> >>>>
> >>>> piston count does not "increase" pressure. it can improve braking
> >>>> because mechanical elasticity becomes less of a concern, and thus you
> >>>> can have a more effective brake for less weight [and money].
> >>>
> >>> Increasing the total piston area increases the applied force for a given
> >>> brake line hydraulic pressure.
> >>
> >> absolutely, but absent ed's "actual piston sizes", we can't say that.
> >
> > Nope, but we can reasonably assume that the total piston area is larger
> > on the Super Duty series calipers than on the F150 calipers.
>
> there is no point in increasing the total piston areas. see below.

Of course there is.

>
> >
> >>
> >>> If for example the F150 calipers had a
> >>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
> >>> the applied clamping force on the rotor would double given the same
> >>> hydraulic pressure.
> >>
> >> if the master piston diameter stays the same. but because of the
> >> leverage ratio, and the limited amount of brake pedal travel available,
> >> ratios typically remain close. [given a long enough pedal travel, you
> >> could dispense with brake boosters.]
> >
> > Larger brake boosters (or hydroboost) allow for larger master cylinder
> > diameters increasing volume without increasing pedal travel.
>
> - to keep the relative ratios fairly constant.
>
> by definition, if the slave area doubles, the master must also double or
> the pedal travel will double. the latter is clearly impracticable -
> there is very little latitude to vary these ratios, and certainly not by
> a factor of two.

The master can double as readily as the slaves can.

>
> >
> >>
> >>> The displacement and required fluid of course would
> >>> also double.
> >>>
> >>>>
> >>>> and as for "weight improving traction" [this is going to be a classic] -
> >>>> why exactly does increasing weight increase stopping distance ed? go
> >>>> on, give it a shot.
> >>>
> >>> The short answer is that increasing weight does not automatically
> >>> increase stopping distance. There is something of a dip in the stopping
> >>> distance where the stopping distance decreases as weight is added up to
> >>> a point before the stopping distance begins to increase again as further
> >>> weight is added.
> >>>
> >>> What happens is that an axle that is too lightly loaded (such as the
> >>> rear in an unloaded pickup) is not able to apply the full available
> >>> braking force without wheel lockup so that the effective braking
> >>> capacity is limited by the lack of traction. As weight is added,
> >>> traction improves allowing more brake force to be applied without
> >>> lockup, resulting in shorter stopping distances. Once there is enough
> >>> weigh to provide sufficient traction to match the maximum braking force
> >>> available, that will be the shorted stopping distance in the graph.
> >>> Additional weight past this point will again increase the stopping
> >>> distance.
> >>
> >> that's a function of two things: tire contact area and control. if
> >> tires are over-inflated relative to load, contact area is reduced.
> >> that's introducing an additional variable rather than talking braking
> >> physics. same for control - if it's too cheap or ineffective to not be
> >> proportioning relative to weight, again, the solution is not to load
> >> more weight, it's to exercise better control.
> >
> > It has nothing to do with control,
>
> then, with respect, you don't understand what "control" means.

Of course I do.

>
> > it has everything to do with a light
> > weight which provides insufficient traction weight on the axle to give
> > the traction necessary to utilize the brakes full capacity.
>
> that's adding weight to increase tire contact area, not braking capacity.

Added weight increases traction (both tire contact area and tire contact
pressure) which allows the use of more of the brakes capacity.
Insufficient traction prevents the use of the brakes full capacity.


>
> > Proportioning and ABS both work to limit the applied brake force to a
> > level that the traction can support, in effect reducing the braking
> > capacity.
>
> they don't "decrease" braking capacity, they decrease skidding.
> skidding isn't braking capacity.

They decrease the braking force applied and thus the percentage of the
braking capacity available in order to prevent skidding when there is
insufficient traction.

>
> > When added weight adds traction, more of the available braking
> > force can be utilized.
>
> KE = 1/2 M.V^2
>
> if you add weight, you increase the amount of braking required.

When that increased weigh has also provided the traction necessary to
utilize more of your existing braking capacity it does not increase your
stopping distance. When you already have sufficient traction to utilize
your full braking capacity, additional weight increases stopping
distance.

"C. E. White" > wrote in message
...
> In this context, the dual pistons are on the same side of the caliper. The
> brakes are still sliding caliper types, just with two pistons side by side
> on one side of the caliper. I haven't found the actual piston sizes, but I
> assume the F250+ brakes can apply significantly more pressure on the rear
> pads than the F150 single piston calipers
>
> Ed
I guess what really stops you is the pressure, in pounds or whatever, that
you apply to the pads. Not PSI, but total pounds, assuming the pad areas
are not changed. One somewhat larger piston can put out as much pressure
as two pistons of somewhat less diameter each. Or have I missed the point.

I can remember when some cars had two and four piston calipers. I believe
that they did not always offer an advantage over a single piston. Will
have
to refresh on this...have slept since then.

On 06/06/2011 01:05 PM, Pete C. wrote:
>
> jim beam wrote:
>>
<snip for brevity>

>> there is no point in increasing the total piston areas. see below.
>
> Of course there is.

ok, so we double the slave area, then we double the master area because
we need to keep the pedal travel the same, then what have we achieved?


>
>>
>>>
>>>>
>>>>> If for example the F150 calipers had a
>>>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
>>>>> the applied clamping force on the rotor would double given the same
>>>>> hydraulic pressure.
>>>>
>>>> if the master piston diameter stays the same. but because of the
>>>> leverage ratio, and the limited amount of brake pedal travel available,
>>>> ratios typically remain close. [given a long enough pedal travel, you
>>>> could dispense with brake boosters.]
>>>
>>> Larger brake boosters (or hydroboost) allow for larger master cylinder
>>> diameters increasing volume without increasing pedal travel.
>>
>> - to keep the relative ratios fairly constant.
>>
>> by definition, if the slave area doubles, the master must also double or
>> the pedal travel will double. the latter is clearly impracticable -
>> there is very little latitude to vary these ratios, and certainly not by
>> a factor of two.
>
> The master can double as readily as the slaves can.

indeed, but to what purpose? provided ratios remain the same, there are
significant reasons not to do so - do you know why?


>
>>
>>>
>>>>
>>>>> The displacement and required fluid of course would
>>>>> also double.
>>>>>
>>>>>>
>>>>>> and as for "weight improving traction" [this is going to be a classic] -
>>>>>> why exactly does increasing weight increase stopping distance ed? go
>>>>>> on, give it a shot.
>>>>>
>>>>> The short answer is that increasing weight does not automatically
>>>>> increase stopping distance. There is something of a dip in the stopping
>>>>> distance where the stopping distance decreases as weight is added up to
>>>>> a point before the stopping distance begins to increase again as further
>>>>> weight is added.
>>>>>
>>>>> What happens is that an axle that is too lightly loaded (such as the
>>>>> rear in an unloaded pickup) is not able to apply the full available
>>>>> braking force without wheel lockup so that the effective braking
>>>>> capacity is limited by the lack of traction. As weight is added,
>>>>> traction improves allowing more brake force to be applied without
>>>>> lockup, resulting in shorter stopping distances. Once there is enough
>>>>> weigh to provide sufficient traction to match the maximum braking force
>>>>> available, that will be the shorted stopping distance in the graph.
>>>>> Additional weight past this point will again increase the stopping
>>>>> distance.
>>>>
>>>> that's a function of two things: tire contact area and control. if
>>>> tires are over-inflated relative to load, contact area is reduced.
>>>> that's introducing an additional variable rather than talking braking
>>>> physics. same for control - if it's too cheap or ineffective to not be
>>>> proportioning relative to weight, again, the solution is not to load
>>>> more weight, it's to exercise better control.
>>>
>>> It has nothing to do with control,
>>
>> then, with respect, you don't understand what "control" means.
>
> Of course I do.

let's come back to that...


>
>>
>>> it has everything to do with a light
>>> weight which provides insufficient traction weight on the axle to give
>>> the traction necessary to utilize the brakes full capacity.
>>
>> that's adding weight to increase tire contact area, not braking capacity.
>
> Added weight increases traction (both tire contact area and tire contact
> pressure) which allows the use of more of the brakes capacity.
> Insufficient traction prevents the use of the brakes full capacity.

the brakes' "full capacity" is locked solid. what you really mean is to
the full capacity of the tire traction. tire compounds being constant,
traction is maximized by maximizing contact area. in that regard, you
should lower your tire pressure before you increase weight.


>
>
>>
>>> Proportioning and ABS both work to limit the applied brake force to a
>>> level that the traction can support, in effect reducing the braking
>>> capacity.
>>
>> they don't "decrease" braking capacity, they decrease skidding.
>> skidding isn't braking capacity.
>
> They decrease the braking force applied and thus the percentage of the
> braking capacity available in order to prevent skidding when there is
> insufficient traction.

abs doesn't decrease pressure, it pulses it so that high pressure is
applied intermittently [in electronics, it's called "pwm", pulse width
modulation].

proportioning valves decrease pressure, but as above, pressure over the
locking value is ineffective. proportioning, done right, /increases/
braking capacity.


>
>>
>>> When added weight adds traction, more of the available braking
>>> force can be utilized.
>>
>> KE = 1/2 M.V^2
>>
>> if you add weight, you increase the amount of braking required.
>
> When that increased weigh has also provided the traction necessary to
> utilize more of your existing braking capacity it does not increase your
> stopping distance. When you already have sufficient traction to utilize
> your full braking capacity, additional weight increases stopping
> distance.

which is a matter of control. when i say you don't understand control,
that's not a pejorative, it's just that you're not fully aware of all
the factors. if you're talking a big rig trailer that is skidding and
not stopping when unladen, that's because of poor control and excess
tire pressure relative to the load. if the brake
anti-lock/proportioning system was better, it wouldn't skid. if tire
pressures were actively managed, as some modern vehicles now are, again,
it wouldn't skid. both are control issues, not "insufficient weight"
issues.


--
nomina rutrum rutrum

jim beam wrote:
>
> On 06/06/2011 01:05 PM, Pete C. wrote:
> >
> > jim beam wrote:
> >>
> <snip for brevity>
>
> >> there is no point in increasing the total piston areas. see below.
> >
> > Of course there is.
>
> ok, so we double the slave area, then we double the master area because
> we need to keep the pedal travel the same, then what have we achieved?

Providing better distribution of the clamping force on the rotors.

>
> >
> >>
> >>>
> >>>>
> >>>>> If for example the F150 calipers had a
> >>>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
> >>>>> the applied clamping force on the rotor would double given the same
> >>>>> hydraulic pressure.
> >>>>
> >>>> if the master piston diameter stays the same. but because of the
> >>>> leverage ratio, and the limited amount of brake pedal travel available,
> >>>> ratios typically remain close. [given a long enough pedal travel, you
> >>>> could dispense with brake boosters.]
> >>>
> >>> Larger brake boosters (or hydroboost) allow for larger master cylinder
> >>> diameters increasing volume without increasing pedal travel.
> >>
> >> - to keep the relative ratios fairly constant.
> >>
> >> by definition, if the slave area doubles, the master must also double or
> >> the pedal travel will double. the latter is clearly impracticable -
> >> there is very little latitude to vary these ratios, and certainly not by
> >> a factor of two.
> >
> > The master can double as readily as the slaves can.
>
> indeed, but to what purpose? provided ratios remain the same, there are
> significant reasons not to do so - do you know why?

Increasing the piston sizes allows more force to be transmitted at a
given hydraulic pressure, much like increasing voltage allows more power
to be transmitted at a given current. Keeping pressures within the
limits of standard components is beneficial. The larger volume of fluid
to be displaced won't have any notable effect since the fluid is
essentially non compressible, this isn't like air brakes and the reasons
for relay valves.

>
> >
> >>
> >>>
> >>>>
> >>>>> The displacement and required fluid of course would
> >>>>> also double.
> >>>>>
> >>>>>>
> >>>>>> and as for "weight improving traction" [this is going to be a classic] -
> >>>>>> why exactly does increasing weight increase stopping distance ed? go
> >>>>>> on, give it a shot.
> >>>>>
> >>>>> The short answer is that increasing weight does not automatically
> >>>>> increase stopping distance. There is something of a dip in the stopping
> >>>>> distance where the stopping distance decreases as weight is added up to
> >>>>> a point before the stopping distance begins to increase again as further
> >>>>> weight is added.
> >>>>>
> >>>>> What happens is that an axle that is too lightly loaded (such as the
> >>>>> rear in an unloaded pickup) is not able to apply the full available
> >>>>> braking force without wheel lockup so that the effective braking
> >>>>> capacity is limited by the lack of traction. As weight is added,
> >>>>> traction improves allowing more brake force to be applied without
> >>>>> lockup, resulting in shorter stopping distances. Once there is enough
> >>>>> weigh to provide sufficient traction to match the maximum braking force
> >>>>> available, that will be the shorted stopping distance in the graph.
> >>>>> Additional weight past this point will again increase the stopping
> >>>>> distance.
> >>>>
> >>>> that's a function of two things: tire contact area and control. if
> >>>> tires are over-inflated relative to load, contact area is reduced.
> >>>> that's introducing an additional variable rather than talking braking
> >>>> physics. same for control - if it's too cheap or ineffective to not be
> >>>> proportioning relative to weight, again, the solution is not to load
> >>>> more weight, it's to exercise better control.
> >>>
> >>> It has nothing to do with control,
> >>
> >> then, with respect, you don't understand what "control" means.
> >
> > Of course I do.
>
> let's come back to that...
>
> >
> >>
> >>> it has everything to do with a light
> >>> weight which provides insufficient traction weight on the axle to give
> >>> the traction necessary to utilize the brakes full capacity.
> >>
> >> that's adding weight to increase tire contact area, not braking capacity.
> >
> > Added weight increases traction (both tire contact area and tire contact
> > pressure) which allows the use of more of the brakes capacity.
> > Insufficient traction prevents the use of the brakes full capacity.
>
> the brakes' "full capacity" is locked solid. what you really mean is to
> the full capacity of the tire traction. tire compounds being constant,
> traction is maximized by maximizing contact area. in that regard, you
> should lower your tire pressure before you increase weight.

Full braking capacity is not "locked solid", that is a static state.
Full braking capacity is the maximum energy dissipation rate the brakes
are capable of while the rotors are still turning.

You need to increase tire pressure as you increase the loading on them
(per tire manufacturers).

>
> >
> >
> >>
> >>> Proportioning and ABS both work to limit the applied brake force to a
> >>> level that the traction can support, in effect reducing the braking
> >>> capacity.
> >>
> >> they don't "decrease" braking capacity, they decrease skidding.
> >> skidding isn't braking capacity.
> >
> > They decrease the braking force applied and thus the percentage of the
> > braking capacity available in order to prevent skidding when there is
> > insufficient traction.
>
> abs doesn't decrease pressure, it pulses it so that high pressure is
> applied intermittently [in electronics, it's called "pwm", pulse width
> modulation].

ABS PWM relies on the time constant of the pistons and calipers to
average the PWM to a lower effective pressure. The same in electronics
where PWM signals are averaged by a low pass filter such as a capacitor,
or by rotor inertia in a PWM motor drive.

>
> proportioning valves decrease pressure, but as above, pressure over the
> locking value is ineffective. proportioning, done right, /increases/
> braking capacity.

Again, these devices are limiting the brake force to match the available
traction, so yes, they are reducing the braking capacity from it's
maximum value.

>
> >
> >>
> >>> When added weight adds traction, more of the available braking
> >>> force can be utilized.
> >>
> >> KE = 1/2 M.V^2
> >>
> >> if you add weight, you increase the amount of braking required.
> >
> > When that increased weigh has also provided the traction necessary to
> > utilize more of your existing braking capacity it does not increase your
> > stopping distance. When you already have sufficient traction to utilize
> > your full braking capacity, additional weight increases stopping
> > distance.
>
> which is a matter of control. when i say you don't understand control,
> that's not a pejorative, it's just that you're not fully aware of all
> the factors. if you're talking a big rig trailer that is skidding and
> not stopping when unladen, that's because of poor control and excess
> tire pressure relative to the load. if the brake
> anti-lock/proportioning system was better, it wouldn't skid. if tire
> pressures were actively managed, as some modern vehicles now are, again,
> it wouldn't skid. both are control issues, not "insufficient weight"
> issues.

Again, it's not at all about control. ABS and proportioning maintain
control by reducing the braking forces to less than the maximum values
which the brakes can sustain, the values that would cause a skid due to
insufficient traction. A vehicle will not be able to achieve the maximum
braking that the brakes are capable of unless it has sufficient load to
achieve enough traction. This is why for many vehicles the stopping
distance decreases as you add cargo weight up until you reach maximum
traction at which point further weight will increase stopping distance.

On 06/06/2011 06:07 PM, Pete C. wrote:
>
> hls wrote:
>>
>> "C. E. > wrote in message
>> ...
>>> In this context, the dual pistons are on the same side of the caliper. The
>>> brakes are still sliding caliper types, just with two pistons side by side
>>> on one side of the caliper. I haven't found the actual piston sizes, but I
>>> assume the F250+ brakes can apply significantly more pressure on the rear
>>> pads than the F150 single piston calipers
>>>
>>> Ed
>> I guess what really stops you is the pressure, in pounds or whatever, that
>> you apply to the pads. Not PSI, but total pounds, assuming the pad areas
>> are not changed. One somewhat larger piston can put out as much pressure
>> as two pistons of somewhat less diameter each. Or have I missed the point.
>>
>> I can remember when some cars had two and four piston calipers. I believe
>> that they did not always offer an advantage over a single piston. Will
>> have
>> to refresh on this...have slept since then.
>
> The main advantage of multi piston calipers is to better distribute the
> clamping force across the pads. A caliper piston can't really be lager
> diameter than the pad is wide, and most pads are not round which leaves
> the overhanging areas not backed by the piston to flex and be less
> effective. Multiple pistons can better cover the area of the pad and
> allow the whole pad area to work more evenly.

I've been told, although don't have enough experience to have felt it
first hand, that for the same piston area, multiple piston calipers tend
to flex less (makes sense) and are therefore easier to modulate. Not as
big a deal with ABS on pretty much everything from the factory today...
but back in the day, being able to modulate your brakes was a Good
Thing. And it still theoretically makes it easier for your ABS to keep
things under control.

nate

--
replace "roosters" with "cox" to reply.
http://members.cox.net/njnagel

On 06/06/2011 03:07 PM, Pete C. wrote:
>
> hls wrote:
>>
>> "C. E. > wrote in message
>> ...
>>> In this context, the dual pistons are on the same side of the caliper. The
>>> brakes are still sliding caliper types, just with two pistons side by side
>>> on one side of the caliper. I haven't found the actual piston sizes, but I
>>> assume the F250+ brakes can apply significantly more pressure on the rear
>>> pads than the F150 single piston calipers
>>>
>>> Ed
>> I guess what really stops you is the pressure, in pounds or whatever, that
>> you apply to the pads. Not PSI, but total pounds, assuming the pad areas
>> are not changed. One somewhat larger piston can put out as much pressure
>> as two pistons of somewhat less diameter each. Or have I missed the point.
>>
>> I can remember when some cars had two and four piston calipers. I believe
>> that they did not always offer an advantage over a single piston. Will
>> have
>> to refresh on this...have slept since then.
>
> The main advantage of multi piston calipers is to better distribute the
> clamping force across the pads. A caliper piston can't really be lager
> diameter than the pad is wide, and most pads are not round which leaves
> the overhanging areas not backed by the piston to flex and be less
> effective. Multiple pistons can better cover the area of the pad and
> allow the whole pad area to work more evenly.

absolutely correct.


--
nomina rutrum rutrum

On 06/06/2011 03:04 PM, Pete C. wrote:
>
> jim beam wrote:
>>
>> On 06/06/2011 01:05 PM, Pete C. wrote:
>>>
>>> jim beam wrote:
>>>>
>> <snip for brevity>
>>
>>>> there is no point in increasing the total piston areas. see below.
>>>
>>> Of course there is.
>>
>> ok, so we double the slave area, then we double the master area because
>> we need to keep the pedal travel the same, then what have we achieved?
>
> Providing better distribution of the clamping force on the rotors.

increasing piston size doesn't do that easily. piston count, as per
your response to hls, is a better solution.


>
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>> If for example the F150 calipers had a
>>>>>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
>>>>>>> the applied clamping force on the rotor would double given the same
>>>>>>> hydraulic pressure.
>>>>>>
>>>>>> if the master piston diameter stays the same. but because of the
>>>>>> leverage ratio, and the limited amount of brake pedal travel available,
>>>>>> ratios typically remain close. [given a long enough pedal travel, you
>>>>>> could dispense with brake boosters.]
>>>>>
>>>>> Larger brake boosters (or hydroboost) allow for larger master cylinder
>>>>> diameters increasing volume without increasing pedal travel.
>>>>
>>>> - to keep the relative ratios fairly constant.
>>>>
>>>> by definition, if the slave area doubles, the master must also double or
>>>> the pedal travel will double. the latter is clearly impracticable -
>>>> there is very little latitude to vary these ratios, and certainly not by
>>>> a factor of two.
>>>
>>> The master can double as readily as the slaves can.
>>
>> indeed, but to what purpose? provided ratios remain the same, there are
>> significant reasons not to do so - do you know why?
>
> Increasing the piston sizes allows more force to be transmitted at a
> given hydraulic pressure, much like increasing voltage allows more power
> to be transmitted at a given current.

it only transmits more pressure if the ratio between master/slave
changes. if that doesn't change, and as we've discussed repeatedly
above there are substantial limitations to that, then it can't.


> Keeping pressures within the
> limits of standard components is beneficial.

yup. that's one.


> The larger volume of fluid
> to be displaced won't have any notable effect since the fluid is
> essentially non compressible, this isn't like air brakes and the reasons
> for relay valves.

right. so what else? there's one particular practical issue that's
very important. apart from cost, weight, etc.


>
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>> The displacement and required fluid of course would
>>>>>>> also double.
>>>>>>>
>>>>>>>>
>>>>>>>> and as for "weight improving traction" [this is going to be a classic] -
>>>>>>>> why exactly does increasing weight increase stopping distance ed? go
>>>>>>>> on, give it a shot.
>>>>>>>
>>>>>>> The short answer is that increasing weight does not automatically
>>>>>>> increase stopping distance. There is something of a dip in the stopping
>>>>>>> distance where the stopping distance decreases as weight is added up to
>>>>>>> a point before the stopping distance begins to increase again as further
>>>>>>> weight is added.
>>>>>>>
>>>>>>> What happens is that an axle that is too lightly loaded (such as the
>>>>>>> rear in an unloaded pickup) is not able to apply the full available
>>>>>>> braking force without wheel lockup so that the effective braking
>>>>>>> capacity is limited by the lack of traction. As weight is added,
>>>>>>> traction improves allowing more brake force to be applied without
>>>>>>> lockup, resulting in shorter stopping distances. Once there is enough
>>>>>>> weigh to provide sufficient traction to match the maximum braking force
>>>>>>> available, that will be the shorted stopping distance in the graph.
>>>>>>> Additional weight past this point will again increase the stopping
>>>>>>> distance.
>>>>>>
>>>>>> that's a function of two things: tire contact area and control. if
>>>>>> tires are over-inflated relative to load, contact area is reduced.
>>>>>> that's introducing an additional variable rather than talking braking
>>>>>> physics. same for control - if it's too cheap or ineffective to not be
>>>>>> proportioning relative to weight, again, the solution is not to load
>>>>>> more weight, it's to exercise better control.
>>>>>
>>>>> It has nothing to do with control,
>>>>
>>>> then, with respect, you don't understand what "control" means.
>>>
>>> Of course I do.
>>
>> let's come back to that...
>>
>>>
>>>>
>>>>> it has everything to do with a light
>>>>> weight which provides insufficient traction weight on the axle to give
>>>>> the traction necessary to utilize the brakes full capacity.
>>>>
>>>> that's adding weight to increase tire contact area, not braking capacity.
>>>
>>> Added weight increases traction (both tire contact area and tire contact
>>> pressure) which allows the use of more of the brakes capacity.
>>> Insufficient traction prevents the use of the brakes full capacity.
>>
>> the brakes' "full capacity" is locked solid. what you really mean is to
>> the full capacity of the tire traction. tire compounds being constant,
>> traction is maximized by maximizing contact area. in that regard, you
>> should lower your tire pressure before you increase weight.
>
> Full braking capacity is not "locked solid", that is a static state.

sorry, it is. if the brake can't lock the wheel, it's ineffective.


> Full braking capacity is the maximum energy dissipation rate the brakes
> are capable of while the rotors are still turning.

and dissipation is caused by? and what energy are we dissipating?


>
> You need to increase tire pressure as you increase the loading on them
> (per tire manufacturers).

and [theoretically] decrease it as you reduce the load again! there are
practical limitations of course, but anyone who goes off-road and
scrambles loose surfaces knows this first hand.


>
>>
>>>
>>>
>>>>
>>>>> Proportioning and ABS both work to limit the applied brake force to a
>>>>> level that the traction can support, in effect reducing the braking
>>>>> capacity.
>>>>
>>>> they don't "decrease" braking capacity, they decrease skidding.
>>>> skidding isn't braking capacity.
>>>
>>> They decrease the braking force applied and thus the percentage of the
>>> braking capacity available in order to prevent skidding when there is
>>> insufficient traction.
>>
>> abs doesn't decrease pressure, it pulses it so that high pressure is
>> applied intermittently [in electronics, it's called "pwm", pulse width
>> modulation].
>
> ABS PWM relies on the time constant of the pistons and calipers to
> average the PWM to a lower effective pressure.

no, the pressure starts high, just like a non-abs brake, then gets cut
by the abs system momentarily before reapplication. it doesn't
"average" a low pressure, it averages a lower braking force.


> The same in electronics
> where PWM signals are averaged by a low pass filter such as a capacitor,
> or by rotor inertia in a PWM motor drive.

you misunderstand pwm. put a capacitor across the poles of a pwm-driven
dc motor and tell me what happens. seriously.


>
>>
>> proportioning valves decrease pressure, but as above, pressure over the
>> locking value is ineffective. proportioning, done right, /increases/
>> braking capacity.
>
> Again, these devices are limiting the brake force to match the available
> traction, so yes, they are reducing the braking capacity from it's
> maximum value.

preventing lock-up is increasing braking capacity, not reducing it. by
definition.


>
>>
>>>
>>>>
>>>>> When added weight adds traction, more of the available braking
>>>>> force can be utilized.
>>>>
>>>> KE = 1/2 M.V^2
>>>>
>>>> if you add weight, you increase the amount of braking required.
>>>
>>> When that increased weigh has also provided the traction necessary to
>>> utilize more of your existing braking capacity it does not increase your
>>> stopping distance. When you already have sufficient traction to utilize
>>> your full braking capacity, additional weight increases stopping
>>> distance.
>>
>> which is a matter of control. when i say you don't understand control,
>> that's not a pejorative, it's just that you're not fully aware of all
>> the factors. if you're talking a big rig trailer that is skidding and
>> not stopping when unladen, that's because of poor control and excess
>> tire pressure relative to the load. if the brake
>> anti-lock/proportioning system was better, it wouldn't skid. if tire
>> pressures were actively managed, as some modern vehicles now are, again,
>> it wouldn't skid. both are control issues, not "insufficient weight"
>> issues.
>
> Again, it's not at all about control. ABS and proportioning maintain
> control by reducing the braking forces to less than the maximum values
> which the brakes can sustain, the values that would cause a skid due to
> insufficient traction.

it's not about control but abs/proportioning maintain control??? you're
confused.

any brake that works properly should be able to lock its wheel.
whatever conditions that wheel is experiencing. ensuring it /doesn't/
lock is absolutely /all/ about control.


> A vehicle will not be able to achieve the maximum
> braking that the brakes are capable of unless it has sufficient load to
> achieve enough traction.

nope. see above.


> This is why for many vehicles the stopping
> distance decreases as you add cargo weight up until you reach maximum
> traction at which point further weight will increase stopping distance.

nope, it's because the control systems don't work well at low loads.


--
nomina rutrum rutrum

jim beam wrote:
>
> On 06/06/2011 03:04 PM, Pete C. wrote:
> >
> > jim beam wrote:
> >>
> >> On 06/06/2011 01:05 PM, Pete C. wrote:
> >>>
> >>> jim beam wrote:
> >>>>
> >> <snip for brevity>
> >>
> >>>> there is no point in increasing the total piston areas. see below.
> >>>
> >>> Of course there is.
> >>
> >> ok, so we double the slave area, then we double the master area because
> >> we need to keep the pedal travel the same, then what have we achieved?
> >
> > Providing better distribution of the clamping force on the rotors.
>
> increasing piston size doesn't do that easily. piston count, as per
> your response to hls, is a better solution.

Which is what I originally indicated about dual pistons.

>
> >
> >>
> >>>
> >>>>
> >>>>>
> >>>>>>
> >>>>>>> If for example the F150 calipers had a
> >>>>>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
> >>>>>>> the applied clamping force on the rotor would double given the same
> >>>>>>> hydraulic pressure.
> >>>>>>
> >>>>>> if the master piston diameter stays the same. but because of the
> >>>>>> leverage ratio, and the limited amount of brake pedal travel available,
> >>>>>> ratios typically remain close. [given a long enough pedal travel, you
> >>>>>> could dispense with brake boosters.]
> >>>>>
> >>>>> Larger brake boosters (or hydroboost) allow for larger master cylinder
> >>>>> diameters increasing volume without increasing pedal travel.
> >>>>
> >>>> - to keep the relative ratios fairly constant.
> >>>>
> >>>> by definition, if the slave area doubles, the master must also double or
> >>>> the pedal travel will double. the latter is clearly impracticable -
> >>>> there is very little latitude to vary these ratios, and certainly not by
> >>>> a factor of two.
> >>>
> >>> The master can double as readily as the slaves can.
> >>
> >> indeed, but to what purpose? provided ratios remain the same, there are
> >> significant reasons not to do so - do you know why?
> >
> > Increasing the piston sizes allows more force to be transmitted at a
> > given hydraulic pressure, much like increasing voltage allows more power
> > to be transmitted at a given current.
>
> it only transmits more pressure if the ratio between master/slave
> changes. if that doesn't change, and as we've discussed repeatedly
> above there are substantial limitations to that, then it can't.

Sorry, you are very much mistaken.

Example with some arbitrary values:

100# of force applied to a 1 sq in master cylinder = 100 PSI fluid,
applied to a 1 sq in slave cylinder = 100# force on the caliper.

200# of force applied to a 2 sq in master cylinder = 100 PSI fluid,
applied to a 2 sq in slave cylinder = 200# force on the calipers.

Twice the force transmitted, at the same hydraulic pressure. Obviously
master cylinder bores are much smaller than slave cylinder bores, but
that doesn't change the fact that increasing both bores allows more
force to be transmitted without increasing hydraulic pressure.

Simple 1:2 ratio:

100# of force applied to a 1 sq in master cylinder = 100 PSI fluid,
applied to a 2 sq in slave cylinder = 200# force on the caliper.

200# of force applied to a 2 sq in master cylinder = 100 PSI fluid,
applied to a 4 sq in slave cylinder = 400# force on the calipers.

>
> > Keeping pressures within the
> > limits of standard components is beneficial.
>
> yup. that's one.
>
> > The larger volume of fluid
> > to be displaced won't have any notable effect since the fluid is
> > essentially non compressible, this isn't like air brakes and the reasons
> > for relay valves.
>
> right. so what else? there's one particular practical issue that's
> very important. apart from cost, weight, etc.
>
> >
> >>
> >>>
> >>>>
> >>>>>
> >>>>>>
> >>>>>>> The displacement and required fluid of course would
> >>>>>>> also double.
> >>>>>>>
> >>>>>>>>
> >>>>>>>> and as for "weight improving traction" [this is going to be a classic] -
> >>>>>>>> why exactly does increasing weight increase stopping distance ed? go
> >>>>>>>> on, give it a shot.
> >>>>>>>
> >>>>>>> The short answer is that increasing weight does not automatically
> >>>>>>> increase stopping distance. There is something of a dip in the stopping
> >>>>>>> distance where the stopping distance decreases as weight is added up to
> >>>>>>> a point before the stopping distance begins to increase again as further
> >>>>>>> weight is added.
> >>>>>>>
> >>>>>>> What happens is that an axle that is too lightly loaded (such as the
> >>>>>>> rear in an unloaded pickup) is not able to apply the full available
> >>>>>>> braking force without wheel lockup so that the effective braking
> >>>>>>> capacity is limited by the lack of traction. As weight is added,
> >>>>>>> traction improves allowing more brake force to be applied without
> >>>>>>> lockup, resulting in shorter stopping distances. Once there is enough
> >>>>>>> weigh to provide sufficient traction to match the maximum braking force
> >>>>>>> available, that will be the shorted stopping distance in the graph.
> >>>>>>> Additional weight past this point will again increase the stopping
> >>>>>>> distance.
> >>>>>>
> >>>>>> that's a function of two things: tire contact area and control. if
> >>>>>> tires are over-inflated relative to load, contact area is reduced.
> >>>>>> that's introducing an additional variable rather than talking braking
> >>>>>> physics. same for control - if it's too cheap or ineffective to not be
> >>>>>> proportioning relative to weight, again, the solution is not to load
> >>>>>> more weight, it's to exercise better control.
> >>>>>
> >>>>> It has nothing to do with control,
> >>>>
> >>>> then, with respect, you don't understand what "control" means.
> >>>
> >>> Of course I do.
> >>
> >> let's come back to that...
> >>
> >>>
> >>>>
> >>>>> it has everything to do with a light
> >>>>> weight which provides insufficient traction weight on the axle to give
> >>>>> the traction necessary to utilize the brakes full capacity.
> >>>>
> >>>> that's adding weight to increase tire contact area, not braking capacity.
> >>>
> >>> Added weight increases traction (both tire contact area and tire contact
> >>> pressure) which allows the use of more of the brakes capacity.
> >>> Insufficient traction prevents the use of the brakes full capacity.
> >>
> >> the brakes' "full capacity" is locked solid. what you really mean is to
> >> the full capacity of the tire traction. tire compounds being constant,
> >> traction is maximized by maximizing contact area. in that regard, you
> >> should lower your tire pressure before you increase weight.
> >
> > Full braking capacity is not "locked solid", that is a static state.
>
> sorry, it is. if the brake can't lock the wheel, it's ineffective.

A locked brake is dissipating no more energy than an un-applied brake.

>
> > Full braking capacity is the maximum energy dissipation rate the brakes
> > are capable of while the rotors are still turning.
>
> and dissipation is caused by? and what energy are we dissipating?

Brake friction converting the momentum of the vehicle (and thus rotation
of the brake rotor) into heat.

>
> >
> > You need to increase tire pressure as you increase the loading on them
> > (per tire manufacturers).
>
> and [theoretically] decrease it as you reduce the load again! there are
> practical limitations of course, but anyone who goes off-road and
> scrambles loose surfaces knows this first hand.

I don't find many loose surfaces around here, I'm quite good at getting
stuck in teflon-like clay mud around here. Airing down doesn't help much
on that.

>
> >
> >>
> >>>
> >>>
> >>>>
> >>>>> Proportioning and ABS both work to limit the applied brake force to a
> >>>>> level that the traction can support, in effect reducing the braking
> >>>>> capacity.
> >>>>
> >>>> they don't "decrease" braking capacity, they decrease skidding.
> >>>> skidding isn't braking capacity.
> >>>
> >>> They decrease the braking force applied and thus the percentage of the
> >>> braking capacity available in order to prevent skidding when there is
> >>> insufficient traction.
> >>
> >> abs doesn't decrease pressure, it pulses it so that high pressure is
> >> applied intermittently [in electronics, it's called "pwm", pulse width
> >> modulation].
> >
> > ABS PWM relies on the time constant of the pistons and calipers to
> > average the PWM to a lower effective pressure.
>
> no, the pressure starts high, just like a non-abs brake, then gets cut
> by the abs system momentarily before reapplication. it doesn't
> "average" a low pressure, it averages a lower braking force.

Semantics, now you're relying on the elasticity of the tire tread to
average the near lockup of the rotor.

>
> > The same in electronics
> > where PWM signals are averaged by a low pass filter such as a capacitor,
> > or by rotor inertia in a PWM motor drive.
>
> you misunderstand pwm. put a capacitor across the poles of a pwm-driven
> dc motor and tell me what happens. seriously.

I don't misunderstand PWM and I said nothing about putting a capacitor
across a motor, though that is common for RFI suppression.

>
> >
> >>
> >> proportioning valves decrease pressure, but as above, pressure over the
> >> locking value is ineffective. proportioning, done right, /increases/
> >> braking capacity.
> >
> > Again, these devices are limiting the brake force to match the available
> > traction, so yes, they are reducing the braking capacity from it's
> > maximum value.
>
> preventing lock-up is increasing braking capacity, not reducing it. by
> definition.

No, it is limiting the braking capacity to match the available traction,
which is often less than the maximum capacity of the braking system.

>
> >
> >>
> >>>
> >>>>
> >>>>> When added weight adds traction, more of the available braking
> >>>>> force can be utilized.
> >>>>
> >>>> KE = 1/2 M.V^2
> >>>>
> >>>> if you add weight, you increase the amount of braking required.
> >>>
> >>> When that increased weigh has also provided the traction necessary to
> >>> utilize more of your existing braking capacity it does not increase your
> >>> stopping distance. When you already have sufficient traction to utilize
> >>> your full braking capacity, additional weight increases stopping
> >>> distance.
> >>
> >> which is a matter of control. when i say you don't understand control,
> >> that's not a pejorative, it's just that you're not fully aware of all
> >> the factors. if you're talking a big rig trailer that is skidding and
> >> not stopping when unladen, that's because of poor control and excess
> >> tire pressure relative to the load. if the brake
> >> anti-lock/proportioning system was better, it wouldn't skid. if tire
> >> pressures were actively managed, as some modern vehicles now are, again,
> >> it wouldn't skid. both are control issues, not "insufficient weight"
> >> issues.
> >
> > Again, it's not at all about control. ABS and proportioning maintain
> > control by reducing the braking forces to less than the maximum values
> > which the brakes can sustain, the values that would cause a skid due to
> > insufficient traction.
>
> it's not about control but abs/proportioning maintain control??? you're
> confused.

Nope, you're confused. If you do not have the traction to allow the use
of the brakes at their maximum capacity, you are operating at *reduced*
braking, even if you want to twist semantics to claim that ABS or
proportioning are maximizing the (available before skidding) braking.

>
> any brake that works properly should be able to lock its wheel.

The subject of quite a bit of debate, since a locked wheel with the
vehicle moving is not a desired condition.

> whatever conditions that wheel is experiencing. ensuring it /doesn't/
> lock is absolutely /all/ about control.

Yep, ABS is certainly about control, but that control is all about
limiting the brakes to less than their maximum braking capacity to
compensate for inadequate traction.

>
> > A vehicle will not be able to achieve the maximum
> > braking that the brakes are capable of unless it has sufficient load to
> > achieve enough traction.
>
> nope. see above.

Sorry, inadequate traction = less than the brakes maximum braking
capacity.

>
> > This is why for many vehicles the stopping
> > distance decreases as you add cargo weight up until you reach maximum
> > traction at which point further weight will increase stopping distance.
>
> nope, it's because the control systems don't work well at low loads.

Nope, it's because an inadequately loaded axle has little traction and
the brakes on that axle can provide little braking capacity as a result.

The control systems also suck eggs when such a lightly loaded vehicle
with stiff suspension hits a slight bump while braking moderately hard.
This is / was a significant safety hazard with some trucks, including
ones I owned, where you had to watch the road surface and stop braking
at each bump, lets the POS ABS freak out and cause you to loose all
braking and greatly increase your stopping distance. Many NHTSA incident
reports are directly attributed to this ABS fault.

On 06/06/2011 05:49 PM, Pete C. wrote:
>
> jim beam wrote:
>>
>> On 06/06/2011 03:04 PM, Pete C. wrote:
>>>
>>> jim beam wrote:
>>>>
>>>> On 06/06/2011 01:05 PM, Pete C. wrote:
>>>>>
>>>>> jim beam wrote:
>>>>>>
>>>> <snip for brevity>
>>>>
>>>>>> there is no point in increasing the total piston areas. see below.
>>>>>
>>>>> Of course there is.
>>>>
>>>> ok, so we double the slave area, then we double the master area because
>>>> we need to keep the pedal travel the same, then what have we achieved?
>>>
>>> Providing better distribution of the clamping force on the rotors.
>>
>> increasing piston size doesn't do that easily. piston count, as per
>> your response to hls, is a better solution.
>
> Which is what I originally indicated about dual pistons.
>
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>> If for example the F150 calipers had a
>>>>>>>>> single 40mm dia piston and the F250+ calipers had dual 40mm dia pistons,
>>>>>>>>> the applied clamping force on the rotor would double given the same
>>>>>>>>> hydraulic pressure.
>>>>>>>>
>>>>>>>> if the master piston diameter stays the same. but because of the
>>>>>>>> leverage ratio, and the limited amount of brake pedal travel available,
>>>>>>>> ratios typically remain close. [given a long enough pedal travel, you
>>>>>>>> could dispense with brake boosters.]
>>>>>>>
>>>>>>> Larger brake boosters (or hydroboost) allow for larger master cylinder
>>>>>>> diameters increasing volume without increasing pedal travel.
>>>>>>
>>>>>> - to keep the relative ratios fairly constant.
>>>>>>
>>>>>> by definition, if the slave area doubles, the master must also double or
>>>>>> the pedal travel will double. the latter is clearly impracticable -
>>>>>> there is very little latitude to vary these ratios, and certainly not by
>>>>>> a factor of two.
>>>>>
>>>>> The master can double as readily as the slaves can.
>>>>
>>>> indeed, but to what purpose? provided ratios remain the same, there are
>>>> significant reasons not to do so - do you know why?
>>>
>>> Increasing the piston sizes allows more force to be transmitted at a
>>> given hydraulic pressure, much like increasing voltage allows more power
>>> to be transmitted at a given current.
>>
>> it only transmits more pressure if the ratio between master/slave
>> changes. if that doesn't change, and as we've discussed repeatedly
>> above there are substantial limitations to that, then it can't.
>
> Sorry, you are very much mistaken.
>
> Example with some arbitrary values:
>
> 100# of force applied to a 1 sq in master cylinder = 100 PSI fluid,
> applied to a 1 sq in slave cylinder = 100# force on the caliper.
>
> 200# of force applied to a 2 sq in master cylinder = 100 PSI fluid,
> applied to a 2 sq in slave cylinder = 200# force on the calipers.
>
> Twice the force transmitted, at the same hydraulic pressure. Obviously
> master cylinder bores are much smaller than slave cylinder bores, but
> that doesn't change the fact that increasing both bores allows more
> force to be transmitted without increasing hydraulic pressure.
>
> Simple 1:2 ratio:
>
> 100# of force applied to a 1 sq in master cylinder = 100 PSI fluid,
> applied to a 2 sq in slave cylinder = 200# force on the caliper.
>
> 200# of force applied to a 2 sq in master cylinder = 100 PSI fluid,
> applied to a 4 sq in slave cylinder = 400# force on the calipers.

you're not reading what i said. if you want to double the output force
on an hydraulic system, you can increase the piston size, but you will
double the input travel. this is immutable and there is no way around it.


>
>>
>>> Keeping pressures within the
>>> limits of standard components is beneficial.
>>
>> yup. that's one.
>>
>>> The larger volume of fluid
>>> to be displaced won't have any notable effect since the fluid is
>>> essentially non compressible, this isn't like air brakes and the reasons
>>> for relay valves.
>>
>> right. so what else? there's one particular practical issue that's
>> very important. apart from cost, weight, etc.
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>>
>>>>>>>>
>>>>>>>>> The displacement and required fluid of course would
>>>>>>>>> also double.
>>>>>>>>>
>>>>>>>>>>
>>>>>>>>>> and as for "weight improving traction" [this is going to be a classic] -
>>>>>>>>>> why exactly does increasing weight increase stopping distance ed? go
>>>>>>>>>> on, give it a shot.
>>>>>>>>>
>>>>>>>>> The short answer is that increasing weight does not automatically
>>>>>>>>> increase stopping distance. There is something of a dip in the stopping
>>>>>>>>> distance where the stopping distance decreases as weight is added up to
>>>>>>>>> a point before the stopping distance begins to increase again as further
>>>>>>>>> weight is added.
>>>>>>>>>
>>>>>>>>> What happens is that an axle that is too lightly loaded (such as the
>>>>>>>>> rear in an unloaded pickup) is not able to apply the full available
>>>>>>>>> braking force without wheel lockup so that the effective braking
>>>>>>>>> capacity is limited by the lack of traction. As weight is added,
>>>>>>>>> traction improves allowing more brake force to be applied without
>>>>>>>>> lockup, resulting in shorter stopping distances. Once there is enough
>>>>>>>>> weigh to provide sufficient traction to match the maximum braking force
>>>>>>>>> available, that will be the shorted stopping distance in the graph.
>>>>>>>>> Additional weight past this point will again increase the stopping
>>>>>>>>> distance.
>>>>>>>>
>>>>>>>> that's a function of two things: tire contact area and control. if
>>>>>>>> tires are over-inflated relative to load, contact area is reduced.
>>>>>>>> that's introducing an additional variable rather than talking braking
>>>>>>>> physics. same for control - if it's too cheap or ineffective to not be
>>>>>>>> proportioning relative to weight, again, the solution is not to load
>>>>>>>> more weight, it's to exercise better control.
>>>>>>>
>>>>>>> It has nothing to do with control,
>>>>>>
>>>>>> then, with respect, you don't understand what "control" means.
>>>>>
>>>>> Of course I do.
>>>>
>>>> let's come back to that...
>>>>
>>>>>
>>>>>>
>>>>>>> it has everything to do with a light
>>>>>>> weight which provides insufficient traction weight on the axle to give
>>>>>>> the traction necessary to utilize the brakes full capacity.
>>>>>>
>>>>>> that's adding weight to increase tire contact area, not braking capacity.
>>>>>
>>>>> Added weight increases traction (both tire contact area and tire contact
>>>>> pressure) which allows the use of more of the brakes capacity.
>>>>> Insufficient traction prevents the use of the brakes full capacity.
>>>>
>>>> the brakes' "full capacity" is locked solid. what you really mean is to
>>>> the full capacity of the tire traction. tire compounds being constant,
>>>> traction is maximized by maximizing contact area. in that regard, you
>>>> should lower your tire pressure before you increase weight.
>>>
>>> Full braking capacity is not "locked solid", that is a static state.
>>
>> sorry, it is. if the brake can't lock the wheel, it's ineffective.
>
> A locked brake is dissipating no more energy than an un-applied brake.

right, but i didn't say that.


>
>>
>>> Full braking capacity is the maximum energy dissipation rate the brakes
>>> are capable of while the rotors are still turning.
>>
>> and dissipation is caused by? and what energy are we dissipating?
>
> Brake friction converting the momentum of the vehicle (and thus rotation
> of the brake rotor) into heat.

not the momentum, the kinetic energy. momentum is m.v. ke is 1/2.m.v^2


>
>>
>>>
>>> You need to increase tire pressure as you increase the loading on them
>>> (per tire manufacturers).
>>
>> and [theoretically] decrease it as you reduce the load again! there are
>> practical limitations of course, but anyone who goes off-road and
>> scrambles loose surfaces knows this first hand.
>
> I don't find many loose surfaces around here, I'm quite good at getting
> stuck in teflon-like clay mud around here. Airing down doesn't help much
> on that.
>
>>
>>>
>>>>
>>>>>
>>>>>
>>>>>>
>>>>>>> Proportioning and ABS both work to limit the applied brake force to a
>>>>>>> level that the traction can support, in effect reducing the braking
>>>>>>> capacity.
>>>>>>
>>>>>> they don't "decrease" braking capacity, they decrease skidding.
>>>>>> skidding isn't braking capacity.
>>>>>
>>>>> They decrease the braking force applied and thus the percentage of the
>>>>> braking capacity available in order to prevent skidding when there is
>>>>> insufficient traction.
>>>>
>>>> abs doesn't decrease pressure, it pulses it so that high pressure is
>>>> applied intermittently [in electronics, it's called "pwm", pulse width
>>>> modulation].
>>>
>>> ABS PWM relies on the time constant of the pistons and calipers to
>>> average the PWM to a lower effective pressure.
>>
>> no, the pressure starts high, just like a non-abs brake, then gets cut
>> by the abs system momentarily before reapplication. it doesn't
>> "average" a low pressure, it averages a lower braking force.
>
> Semantics, now you're relying on the elasticity of the tire tread to
> average the near lockup of the rotor.

i'm not, the abs system is. and it's not relying on the tire
elasticity, it's relying on the physical inertia of the moving parts.


>
>>
>>> The same in electronics
>>> where PWM signals are averaged by a low pass filter such as a capacitor,
>>> or by rotor inertia in a PWM motor drive.
>>
>> you misunderstand pwm. put a capacitor across the poles of a pwm-driven
>> dc motor and tell me what happens. seriously.
>
> I don't misunderstand PWM and I said nothing about putting a capacitor
> across a motor, though that is common for RFI suppression.

oh, please. and don't waffle, do what i said so you can see what happens.


>
>>
>>>
>>>>
>>>> proportioning valves decrease pressure, but as above, pressure over the
>>>> locking value is ineffective. proportioning, done right, /increases/
>>>> braking capacity.
>>>
>>> Again, these devices are limiting the brake force to match the available
>>> traction, so yes, they are reducing the braking capacity from it's
>>> maximum value.
>>
>> preventing lock-up is increasing braking capacity, not reducing it. by
>> definition.
>
> No, it is limiting the braking capacity to match the available traction,

which is /increasing/ the braking capacity if it's preventing lock-up -
skidding tires don't offer as much traction.


> which is often less than the maximum capacity of the braking system.

no, the "less than" is the applied hydraulic force relative to the
maximum, not the braking force.


>
>>
>>>
>>>>
>>>>>
>>>>>>
>>>>>>> When added weight adds traction, more of the available braking
>>>>>>> force can be utilized.
>>>>>>
>>>>>> KE = 1/2 M.V^2
>>>>>>
>>>>>> if you add weight, you increase the amount of braking required.
>>>>>
>>>>> When that increased weigh has also provided the traction necessary to
>>>>> utilize more of your existing braking capacity it does not increase your
>>>>> stopping distance. When you already have sufficient traction to utilize
>>>>> your full braking capacity, additional weight increases stopping
>>>>> distance.
>>>>
>>>> which is a matter of control. when i say you don't understand control,
>>>> that's not a pejorative, it's just that you're not fully aware of all
>>>> the factors. if you're talking a big rig trailer that is skidding and
>>>> not stopping when unladen, that's because of poor control and excess
>>>> tire pressure relative to the load. if the brake
>>>> anti-lock/proportioning system was better, it wouldn't skid. if tire
>>>> pressures were actively managed, as some modern vehicles now are, again,
>>>> it wouldn't skid. both are control issues, not "insufficient weight"
>>>> issues.
>>>
>>> Again, it's not at all about control. ABS and proportioning maintain
>>> control by reducing the braking forces to less than the maximum values
>>> which the brakes can sustain, the values that would cause a skid due to
>>> insufficient traction.
>>
>> it's not about control but abs/proportioning maintain control??? you're
>> confused.
>
> Nope, you're confused. If you do not have the traction to allow the use
> of the brakes at their maximum capacity, you are operating at *reduced*
> braking, even if you want to twist semantics to claim that ABS or
> proportioning are maximizing the (available before skidding) braking.

abs' sole function is CONTROL.
http://en.wikipedia.org/wiki/Control_theory

it is CONTROL that allows you to maximize braking without skidding.


>
>>
>> any brake that works properly should be able to lock its wheel.
>
> The subject of quite a bit of debate, since a locked wheel with the
> vehicle moving is not a desired condition.

any "debate" is whether a driver can control maximum braking better than
a machine, not whether a braking system should be powerful.


>
>> whatever conditions that wheel is experiencing. ensuring it /doesn't/
>> lock is absolutely /all/ about control.
>
> Yep, ABS is certainly about control, but that control is all about
> limiting the brakes to less than their maximum braking capacity to
> compensate for inadequate traction.

no, it's to maximize available braking and CONTROL. this is why abs was
invented - drivers are typically BAD at CONTROL.


>
>>
>>> A vehicle will not be able to achieve the maximum
>>> braking that the brakes are capable of unless it has sufficient load to
>>> achieve enough traction.
>>
>> nope. see above.
>
> Sorry, inadequate traction = less than the brakes maximum braking
> capacity.

no, CONTROL


>
>>
>>> This is why for many vehicles the stopping
>>> distance decreases as you add cargo weight up until you reach maximum
>>> traction at which point further weight will increase stopping distance.
>>
>> nope, it's because the control systems don't work well at low loads.
>
> Nope, it's because an inadequately loaded axle has little traction and
> the brakes on that axle can provide little braking capacity as a result.

no. and you contradict yourself below.


>
> The control systems also suck eggs when such a lightly loaded vehicle
> with stiff suspension hits a slight bump while braking moderately hard.
> This is / was a significant safety hazard with some trucks, including
> ones I owned, where you had to watch the road surface and stop braking
> at each bump, lets the POS ABS freak out and cause you to loose all
> braking and greatly increase your stopping distance. Many NHTSA incident
> reports are directly attributed to this ABS fault.

so we're back right where we started - if you're experiencing poor
braking, it's because of poor control, not poor physics.


--
nomina rutrum rutrum