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New tyres best on rear wheels?



 
 
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  #1  
Old August 17th 04, 10:29 AM
Alex
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Default New tyres best on rear wheels?

I will be getting two new tyres for my 2000 A3, as the front wheels treads
are wearing. A friend said that new tyres are best on the rear wheels (even
irrespective of whether FWD or RWD). Is this true or a myth?

Cheers




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  #2  
Old August 17th 04, 10:48 AM
Rainer Hausbach
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> I will be getting two new tyres for my 2000 A3, as the front wheels treads
> are wearing. A friend said that new tyres are best on the rear wheels

(even
> irrespective of whether FWD or RWD). Is this true or a myth?
>
> Cheers


it's true.

if you're running e.g. at 40mph on the freeway and your rear wheel breaks,
ther is no way avoiding a serious accident. If It's the front wheel, you
have at least a chanche handling with the new sitiation...
so best wheels belong to the rear!

HTH
Rainer


  #3  
Old August 17th 04, 08:25 PM
Mike Smith
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Juhan Leemet wrote:
>
> I guess I don't understand this. I've experienced a flat rear tire (on an
> American rear wheel drive car many years ago): the car started to "swim"
> (i.e. oversteer?). I guess it's like throwing an anchor out the back?
> However, if a front tire/wheel were to go I would think you would be in
> much more trouble? When the car slows down, it pitches forward. Wouldn't
> that cause the car to spin? Does FWD or AWD make it work differently?


I would agree with this. I've had blowouts on both front and rear
tires, and the front-tire blowout was much more difficult to control.
I'd say you want your best tires on the front with any kind of car, but
*especially* a front-wheel-drive.

--
Mike Smith
  #4  
Old August 17th 04, 10:31 PM
Robert
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Mike Smith wrote:

> Juhan Leemet wrote:
>
>>
>> I guess I don't understand this. I've experienced a flat rear tire (on an
>> American rear wheel drive car many years ago): the car started to "swim"
>> (i.e. oversteer?). I guess it's like throwing an anchor out the back?
>> However, if a front tire/wheel were to go I would think you would be in
>> much more trouble? When the car slows down, it pitches forward. Wouldn't
>> that cause the car to spin? Does FWD or AWD make it work differently?

>
>
> I would agree with this. I've had blowouts on both front and rear
> tires, and the front-tire blowout was much more difficult to control.
> I'd say you want your best tires on the front with any kind of car, but
> *especially* a front-wheel-drive.


No way José. Losing traction on fronts may cause problems with
direction, but you'll stay pointed roughly where you want to go. Losing
grip on the rears can easily cause you to swap ends when trying to stop.

The positive side of this is that rally drivers exploit the phenomenon
in order to corner faster - they set the brake bias more to the rear so
that the back end becomes unstable under braking (and threatens to spin
the car). This allows the car to be (quickly) pointed in the right
direction much earlier in the corner than is usually possible with
"consumer-type" brake balance. You have to be used to it, of course, if
you want to keep the car on the road ;-)

/Robert

  #5  
Old August 18th 04, 12:53 AM
Hairy One Kenobi
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"Mike Smith" > wrote in message
...
> Juhan Leemet wrote:
> >
> > I guess I don't understand this. I've experienced a flat rear tire (on

an
> > American rear wheel drive car many years ago): the car started to "swim"
> > (i.e. oversteer?). I guess it's like throwing an anchor out the back?
> > However, if a front tire/wheel were to go I would think you would be in
> > much more trouble? When the car slows down, it pitches forward. Wouldn't
> > that cause the car to spin? Does FWD or AWD make it work differently?

>
> I would agree with this. I've had blowouts on both front and rear
> tires, and the front-tire blowout was much more difficult to control.
> I'd say you want your best tires on the front with any kind of car, but
> *especially* a front-wheel-drive.


The precise opposite.

While I've only experienced one blow-out (FWD car, braking heavily at 60mph
down a 1:6 hill on a tight right-hand bend, left front blew. Fun..), the
whole idea of a car swapping-ends while I'm trying to work out what's going
on is.. frightening.

Having had the equivalent happen to me (stuck brake bias valve in a new
Citroen AX GT), I can confirm that wrestling a car with locked rear wheels
(same as bald tyres, if you see what I mean!) while some part is doing a
720* in front of you is.. distracting, at best.

If you want a /really/ fun afternoon, add a throttle that stuck to the floor
the first time that it was used in anger (I was still running/"breaking"
in..)

Anyway.

In general, understeer (even unexpected) is easier to deal with than
oversteer. If you fit grippy tyres to the front, and skates to the back,
then you're going to get oversteer. Even in an [old] Mini, where the rear
wheels are then solely to stop you scraping the chrome off of the bumper.

*Always* fit new tyres to the rear, then (as soon as money allows) replace
the front. Particularly on FWD cars, where the weight transfer under braking
will leave the rear *seriously* light.

--

Hairy One Kenobi

Disclaimer: the opinions expressed in this opinion do not necessarily
reflect the opinions of the highly-opinionated person expressing the opinion
in the first place. So there!


  #6  
Old August 18th 04, 08:07 PM
C.R. Krieger
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Mike Smith > wrote in message >...
> Juhan Leemet wrote:
> >
> > I guess I don't understand this. I've experienced a flat rear tire (on an
> > American rear wheel drive car many years ago): the car started to "swim"
> > (i.e. oversteer?). Wouldn't that cause the car to spin?


What causes a spin is the rear wheels. Period. Doesn't matter if
they're driven or not. If your front end slides, the front end stays
in front. If the rear end slides, the rear end tries to pass the
front (a spin). The real cause is, sliding friction is less than
static friction, so the sliding wheels tend to go faster than the
non-sliding wheels, but we're not going into all that. Just remember
that the end where the wheels are sliding will go to the front in the
direction of the slide.

> Does FWD or AWD make it work differently?


None whatsoever.

> I would agree with this. I've had blowouts on both front and rear
> tires, and the front-tire blowout was much more difficult to control.


The problem with both your analyses is that you're assuming the only
time this matters is with a blowout. You can count the number of
times you've experienced a blowout on one hand (I hope!). At least I
can, in about 35 years of driving, including a number of teen years on
'Bald Eagles'.

Having less (or worse) traction at the rear of the car is something
you have to deal with *every single time you reach the limits of
traction*! For the average driver, that occurs most often in reduced
traction conditions like rain, snow, or loose surfaces. It also
happens whether you're turning or going straight. It can even happen
under acceleration in a RWD or AWD car if the rear loses traction.
Acceleration is the *only* condition under which it matters where the
drive wheels are, and a FWD will have a natural directional advantage
here that's not negated by having better tires on the rear.

Because of the tendency of the lower traction end of the car to lead
in a slide, if the rears break traction under braking, the car can
swap ends. If the rears break traction while cornering, they tend to
slide off the outside of the turn in a perpendicular (to the tangent)
line from the point at which they broke loose. Either way, you end up
with the taillights leading the way. Most people think of this as a
Bad Thing (TM).

> I'd say you want your best tires on the front with any kind of car, but
> *especially* a front-wheel-drive.


That depends on whether you prefer sliding butt-end first or whether
you want to *see* what you hit. Frankly, if it's raining, I want the
back end of the car to stay back there, so *my* good tires are always
on the rear, no matter what the drivetrain configuration happens to
be.
--
C.R. Krieger
(Been there; done that)
  #7  
Old August 18th 04, 11:06 PM
Mike Smith
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C.R. Krieger wrote:
>
> The problem with both your analyses is that you're assuming the only
> time this matters is with a blowout.


No, but that's one of the time that it matters *most*.

> You can count the number of
> times you've experienced a blowout on one hand (I hope!).


Well, twice, like I said.

> Having less (or worse) traction at the rear of the car is something
> you have to deal with *every single time you reach the limits of
> traction*! For the average driver, that occurs most often in reduced
> traction conditions like rain, snow, or loose surfaces. It also
> happens whether you're turning or going straight. It can even happen
> under acceleration in a RWD or AWD car if the rear loses traction.
> Acceleration is the *only* condition under which it matters where the
> drive wheels are, and a FWD will have a natural directional advantage
> here that's not negated by having better tires on the rear.


This is all true. But then again, I don't make a habit of driving on
bald tires!

--
Mike Smith
  #8  
Old August 19th 04, 08:49 PM
C.R. Krieger
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Mike Smith > wrote in message >...
> C.R. Krieger wrote:
> >
> > The problem with both your analyses is that you're assuming the only
> > time this matters is with a blowout.

>
> No, but that's one of the time that it matters *most*.


Not really. I didn't want to spend a whole lot of time explaining why
a suddenly deflated tire is pretty much a 'non-event', but it with
modern suspension systems, it really is. While it might *feel* pretty
weird, your chances of actually losing control as a result are almost
as slim as having it happen in the first place.

> > You can count the number of
> > times you've experienced a blowout on one hand (I hope!).

>
> Well, twice, like I said.


Out of how many *cars* you've driven? The strongest odds are that you
*won't* experience a blowout in a given car, so why would you
sacrifice safer handling *all the time* for a supposedly extreme event
that probably won't occur?

> > Having less (or worse) traction at the rear of the car is something
> > you have to deal with *every single time you reach the limits of
> > traction*! For the average driver, that occurs most often in reduced
> > traction conditions like rain, snow, or loose surfaces. It also
> > happens whether you're turning or going straight. It can even happen
> > under acceleration in a RWD or AWD car if the rear loses traction.
> > Acceleration is the *only* condition under which it matters where the
> > drive wheels are, and a FWD will have a natural directional advantage
> > here that's not negated by having better tires on the rear.

>
> This is all true. But then again, I don't make a habit of driving on
> bald tires!


I'm not talking about bald tires. Frankly, in dry conditions, you
*want* bald tires because they actually offer the most traction.
However the tradeoff, as any of the eight Speed GT Series drivers who
ended up off the last turn at Watkins Glen a few weeks ago will tell
you, is that slicks really suck in rain. Even full-treaded tires can
lose traction depending on the circumstances. Therefore, the smartest
thing is to have the 'best' ones on the rear all the time.
--
C.R. Krieger
(Been there; done that)
  #9  
Old August 19th 04, 09:03 PM
C.R. Krieger
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Juhan Leemet > wrote in message om>...
>
> Good explanations. Thanks!


You're welcome.

> FWIW, these days I'm driving an AWD Subaru (can't affort Quattro), so I'm
> buying new tires all round. They say that any mismatch in tire size causes
> the transmission to have problems ("blow up"?) so I'm not taking chances.
> I guess I'm avoiding bad rear traction problems as a freebie?


Not the transmission; the differential. Never actually heard of one
blowing up, either, even as sorely abused as some of 'em must be. As
long as your nominal tire size (outside circumference) is close to the
same, I wouldn't worry about it too much.

> I have to say that driving AWD "feels different" from RWD or FWD. I guess
> that's obvious? What's not so obvious to me is how to "get the hang of
> it". Whenever there's some snow, I try to find some clear space to
> "practice" slides, and handling when various wheels are "breaking free".


You need to learn that you'll still have FWD-style understeer at low
speeds and more neutral handling at higher ones.

> Thinking some more about it, I guess having good tires all around does not
> prevent spins. As you brake, the car pitches forward and you get more
> braking action from the front tires, and less weight (and hence frictional
> force) on the back tires. If they break free, they can still spin the car.


Bingo!

> I guess AWD driving technique is more like FWD? You should plan on braking
> early, then "powering though" turns: i.e. point in the direction you want
> to go and (gently) apply accelerator, not brakes?


The fastest way through turns with FWD is to add a touch of braking
when the front starts to slide (understeer) to induce some oversteer.
You can gently experiment with the handbrake on curves, if you're
adventurous and you want to feel the transition from under- to
oversteer. Rally drivers discovered this decades ago.

With AWD, you can lift off the throttle *if* you get understeer. You
can also accelerate until it starts to slide and get onto the gas
earlier because of the power distribution (which doesn't tend to
overload either end of the car when you do it). It's simply much more
forgiving.

> OTOH, I think I've
> experienced a sudden "oversteer" that resulted when the tires started to
> grip: the front wheels were pointed where I wanted to go and started to
> turn that way, but the rear wheels had some power applied towards the
> outside of the turn.


Could happen ...
--
C.R. Krieger
(Been there; done that)
 




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