Tire Pressure?

Hi,

My E39 528 has several tire pressure rating on the door panel. Which is the
right one?

F/R
33/41 for US/Can
29/33 outside US/Can

Does anyone know why is that? And which is really correct?

Although it seems clear from the above, it is not so when Canadian garages
(BMW Service) insists the 33/41 is too high!

there are different wheel package for this car and they have recommendations
that vary

there is usually a published guideline, if not on the door, then in the
manual.






"ppp-man" > wrote in message
news:dJcLd.81920$Ob.72242@edtnps84...
> Hi,
>
> My E39 528 has several tire pressure rating on the door panel. Which is
> the right one?
>
> F/R
> 33/41 for US/Can
> 29/33 outside US/Can
>
> Does anyone know why is that? And which is really correct?
>
> Although it seems clear from the above, it is not so when Canadian garages
> (BMW Service) insists the 33/41 is too high!
>

ONCE AGAIN, let's get this understood.

There is NO SUCH THING as the "correct" tire pressure. The only tire
pressure you need to be aware of is the MAX PRESSURE on the sidewall of your
tires. Go above this and you risk a blow out.

Other than that you are free to use any pressure you like, depending on
whether you are looking to enhance handling, traction, tread life, ride
comfort, etc. Do some research on how pressure affects tire
wear/performance and you will have a very good understanding of what
pressures you may want to try INITIALLY. I say initially because you are
free to tweak the settings to your liking.

While the settings are less critical on my 740, which I do not drive
aggressively or on the track, they are critical on my M5 and M3. The M5 sees
some track time, while the M3 is strictly track. I adjust the M5 tires
before and during track runs every time I go out.



"ppp-man" > wrote in message
news:dJcLd.81920$Ob.72242@edtnps84...
> Hi,
>
> My E39 528 has several tire pressure rating on the door panel. Which is
> the right one?
>
> F/R
> 33/41 for US/Can
> 29/33 outside US/Can
>
> Does anyone know why is that? And which is really correct?
>
> Although it seems clear from the above, it is not so when Canadian garages
> (BMW Service) insists the 33/41 is too high!
>

Thanks for the mind-expanding knowledge.

To get started though, what would you say about the 'stock' recommended
pressures? At 29/33 (f/r) what kind of ride would it mean to you? Or more
correctly, at what ever your door plat recommends as the 'nominal' pressure,
what does it ride like?


"tech27" > wrote in message
o.verio.net...
> ONCE AGAIN, let's get this understood.
>
> There is NO SUCH THING as the "correct" tire pressure. The only tire
> pressure you need to be aware of is the MAX PRESSURE on the sidewall of
> your tires. Go above this and you risk a blow out.
>
> Other than that you are free to use any pressure you like, depending on
> whether you are looking to enhance handling, traction, tread life, ride
> comfort, etc. Do some research on how pressure affects tire
> wear/performance and you will have a very good understanding of what
> pressures you may want to try INITIALLY. I say initially because you are
> free to tweak the settings to your liking.
>
> While the settings are less critical on my 740, which I do not drive
> aggressively or on the track, they are critical on my M5 and M3. The M5
> sees some track time, while the M3 is strictly track. I adjust the M5
> tires before and during track runs every time I go out.
>
>
>
> "ppp-man" > wrote in message
> news:dJcLd.81920$Ob.72242@edtnps84...
>> Hi,
>>
>> My E39 528 has several tire pressure rating on the door panel. Which is
>> the right one?
>>
>> F/R
>> 33/41 for US/Can
>> 29/33 outside US/Can
>>
>> Does anyone know why is that? And which is really correct?
>>
>> Although it seems clear from the above, it is not so when Canadian
>> garages (BMW Service) insists the 33/41 is too high!
>>
>
>

"ppp-man" > wrote in message
news:1MkMd.4$dI4.0@edtnps91...
> Thanks for the mind-expanding knowledge.
>
> To get started though, what would you say about the 'stock'
> recommended pressures? At 29/33 (f/r) what kind of ride would it
> mean to you? Or more correctly, at what ever your door plat
> recommends as the 'nominal' pressure, what does it ride like?

The tire pressure recomended by the manufacturer (on the door jamb) is
a compromise likely to give you the softest ride with the most even
tire wear for that size tire on that car. Generally, I do not inflate
my tires to anything less, but will often increase the pressure some
to reduce the side wall flex and roll-over during more "spirited"
driving.

-Fred W

"tech27" > wrote in message
o.verio.net...
> ONCE AGAIN, let's get this understood.
>
> There is NO SUCH THING as the "correct" tire pressure. The only tire
> pressure you need to be aware of is the MAX PRESSURE on the sidewall of
your
> tires. Go above this and you risk a blow out.
>

And pressure that even begins to approach the max tire pressure printed on
the sidewall is WAY TOO MUCH PRESSURE for "normal" driving conditions.


The rule of thumb if you can't find the actual sticker that tells you what
to put in is to put in 30psi, or 2 BAR. This is generally accepted as the
perfect pressure because if you need 2 pounds more or 2 pounds less, you'll
never know.

No matter how much air you put in, if you keep an eye on the tire wear, you
can make adjustments from time to time. Even with the "right" pressure,
you'll need to make adjustments. If the tires are wearing on the shoulders
where the tread rolls over and becomes sidewall, then you have too little
air pressure. If the tires wear in the center of the tread, then you have
too much air pressure. If the front tires wear on one shoulder but not the
others (4 total shoulders to look at), or wear on the outside shoulders but
not the inside, you have alignment troubles - maybe air pressure as well,
but alignment for sure - and if the rear tires wear on the inside shoulders
more than on the outside, then you have problems with overly aggressive
operation of the fuel supply mechanism - gas pedal.

There are other things that cause tire wear that have to do with alignment,
but I have to assume that the alignment is good when I talk about tire wear
that is caused by air pressure. Most tire wear that you see on other cars as
you are sitting at a traffic light or stuck on a clogged freeway is caused
by poor inflation practices. Once you take notice of other people's tires
and how they wear evenly, that is both (or all four) shoulders are worn on
the front tires, then you will be able to notice wear from alignment vs wear
from poor inflation practices.

Take notice of the rear tires on a pick up truck. These are generally worn
in the center, which is a sign of over inflation. When you see the various
wear patterns on other cars, then you will be able to tell what your own car
is doing.





> Other than that you are free to use any pressure you like, depending on
> whether you are looking to enhance handling, traction, tread life, ride
> comfort, etc. Do some research on how pressure affects tire
> wear/performance and you will have a very good understanding of what
> pressures you may want to try INITIALLY. I say initially because you are
> free to tweak the settings to your liking.
>
> While the settings are less critical on my 740, which I do not drive
> aggressively or on the track, they are critical on my M5 and M3. The M5
sees
> some track time, while the M3 is strictly track. I adjust the M5 tires
> before and during track runs every time I go out.
>
>
>
> "ppp-man" > wrote in message
> news:dJcLd.81920$Ob.72242@edtnps84...
> > Hi,
> >
> > My E39 528 has several tire pressure rating on the door panel. Which is
> > the right one?
> >
> > F/R
> > 33/41 for US/Can
> > 29/33 outside US/Can
> >
> > Does anyone know why is that? And which is really correct?
> >
> > Although it seems clear from the above, it is not so when Canadian
garages
> > (BMW Service) insists the 33/41 is too high!
> >
>
>

Well, I'd just be guessing, but the "recommended" inflation numbers on most
cars are just that - recommended- which means they probably give the best
"overall" ride - overall meaning what the car manufacturer thinks the buyer
of the car is looking for. For a luxury car it would mean comfortable ride,
for a performance car it would probably be a compromise between good
handling and comfort.

But if you are looking to increase comfort, you are probably looking at a
lower pressure (maybe-depending on what the recommendation is). One
universal truth is that the more weight you pack in the car, the higher your
pressure should be.

Here is a good link to look at:

http://www.tirerack.com/tires/tirete...n/racepres.jsp


It shows many parameters besides tire pressure, but you'll get the idea. For
tire pressure (first 2). Remember that although the headings are for
Decreasing Under/Over Steer you can substitute Increase for Decrease and
change the Higher to Lower where indicated. Now you can get really confused
and complicate things by changing JUST the front or JUST the rear, or a
combination of increase or decrease on JUST the front or JUST the rear.

Many have gone insane trying to understand this and the front/rear
interactions. It's really a matter of trial and error. Just keep the
pressures below the MAX indicated on the tire wall.

For instance - I don't even remember what the recommended pressures are for
my M5. I think 34/38 but I'm just guessing. At the track I set all 4 to 36
psi, then adjust from there. I'm not that good a driver to completely assess
the effect of small changes, but my instructor told me to change the
pressures after a few laps to something different for the fronts and
different again for the rears. And AGAIN, this might change from track to
track depending on the track itself (surface and condition) as well as
dry/wet and temperature.


"ppp-man" > wrote in message news:1MkMd.4$dI4.0@edtnps91...
> Thanks for the mind-expanding knowledge.
>
> To get started though, what would you say about the 'stock' recommended
> pressures? At 29/33 (f/r) what kind of ride would it mean to you? Or
> more correctly, at what ever your door plat recommends as the 'nominal'
> pressure, what does it ride like?
>
>
> "tech27" > wrote in message
> o.verio.net...
>> ONCE AGAIN, let's get this understood.
>>
>> There is NO SUCH THING as the "correct" tire pressure. The only tire
>> pressure you need to be aware of is the MAX PRESSURE on the sidewall of
>> your tires. Go above this and you risk a blow out.
>>
>> Other than that you are free to use any pressure you like, depending on
>> whether you are looking to enhance handling, traction, tread life, ride
>> comfort, etc. Do some research on how pressure affects tire
>> wear/performance and you will have a very good understanding of what
>> pressures you may want to try INITIALLY. I say initially because you are
>> free to tweak the settings to your liking.
>>
>> While the settings are less critical on my 740, which I do not drive
>> aggressively or on the track, they are critical on my M5 and M3. The M5
>> sees some track time, while the M3 is strictly track. I adjust the M5
>> tires before and during track runs every time I go out.
>>
>>
>>
>> "ppp-man" > wrote in message
>> news:dJcLd.81920$Ob.72242@edtnps84...
>>> Hi,
>>>
>>> My E39 528 has several tire pressure rating on the door panel. Which is
>>> the right one?
>>>
>>> F/R
>>> 33/41 for US/Can
>>> 29/33 outside US/Can
>>>
>>> Does anyone know why is that? And which is really correct?
>>>
>>> Although it seems clear from the above, it is not so when Canadian
>>> garages (BMW Service) insists the 33/41 is too high!
>>>
>>
>>
>
>

"The Malt Hound" <Malt_Hound@*no spam please*yahoo.com> wrote in message
...
> The tire pressure recomended by the manufacturer (on the door jamb) is a
> compromise likely to give you the softest ride with the most even tire
> wear for that size tire on that car. Generally, I do not inflate my tires
> to anything less, but will often increase the pressure some to reduce the
> side wall flex and roll-over during more "spirited" driving.
>
> -Fred W

Fair enough FW, but depending on how hard you drive it, and whether it is on
the street or track, sidewall flex is not always a bad thing. Appropriate
flex also allows the tire to stay firmly planted for maximum traction. If
you sidewalls had no flex at all, you'd be pulling the outside of the tire
off the track in a hard turn (outside of driver side tires going into a hard
left).

"Jeff Strickland" > wrote in message
...
>
> And pressure that even begins to approach the max tire pressure printed on
> the sidewall is WAY TOO MUCH PRESSURE for "normal" driving conditions.

Agreed. The Max Pressure is really just an imprinted idiot light.


> > Take notice of the rear tires on a pick up truck. These are generally
> > worn
> in the center, which is a sign of over inflation. When you see the various
> wear patterns on other cars, then you will be able to tell what your own
> car
> is doing.

And this is usually due to the fact that the owner inflated it to spec when
carring a very heavy load (for 5% of the time), then never bothered to
change it when the bed is empty (for most of the time.

"tech27" > wrote in message
o.verio.net...
>
> "The Malt Hound" <Malt_Hound@*no spam please*yahoo.com> wrote in
> message ...
>> The tire pressure recomended by the manufacturer (on the door jamb)
>> is a compromise likely to give you the softest ride with the most
>> even tire wear for that size tire on that car. Generally, I do not
>> inflate my tires to anything less, but will often increase the
>> pressure some to reduce the side wall flex and roll-over during
>> more "spirited" driving.
>>
>> -Fred W
>
> Fair enough FW, but depending on how hard you drive it, and whether
> it is on the street or track, sidewall flex is not always a bad
> thing. Appropriate flex also allows the tire to stay firmly planted
> for maximum traction. If you sidewalls had no flex at all, you'd be
> pulling the outside of the tire off the track in a hard turn
> (outside of driver side tires going into a hard left).


Radial tires will always have (relatively) supple sidewalls. What
*will* happen under extreme cornering if the tires are too soft is the
whole tread patch shifts opposite to the g-force. this causes the
contact patch to roll and you lose contact on the inside edge.

It's quite easy to test by using chalk marks, and this actually can be
used to find the optimum tire pressure for any driving style or
conditions (except wet ones). Make a heavy chalk mark across the face
of the tread on each wheel. Drive the car in the intended fashion for
a short distance and then stop and observe the wear pattern of the
chalk marks.

For autocrossing or racing you are looking to get the best even wear
of the inboard edge compared to the outboard edge of each tire after
extreme cornering.

For best tire wear you are looking to balance the center wear with the
outside edges.

-Fred W