AWD car needs a new tire; Replace one or all 4

Went to Firestone today because I have a slow leak in one of my tires.
The car is a 2002 Subaru Impreza TS with factory spec tires 195/60/R15.
Turns out the slow leak was due to a puncture in the sidewall of the
tire, so that tire is garbage. The tires are all about a year old and
have decent meat on them, but the tech said you can't just replace one
tire on an AWD car, you have to replace all 4 as a set, because the new
one will be some sixteenths of an inch larger than all the rest.

Of course he'd say that

Now, I understand the concept and theory of this- if all wheels are the
same circumference, they all rotate the same amount and internal
drivetrain components (center diff or viscous clutch) don't have to take
up the slack. But... I have a hard time believing that an amount
measured in sixteenths of an inch is significant. Surely a few pounds
of pressure off, or an unbalanced load (i.e., some fatass sitting in a
seat opposite some 80 pound child) would make just as much difference?

I declined to make any purchase at this time. I know I'll need to
replace that one tire, but I have another vehicle to drive for now. I
would like to replace the one tire only. Replacing all 4 is a bit
unnecessary, right?

Thanks

-J

On Jan 10, 8:51*am, phaeton > wrote:
> Went to Firestone today because I have a slow leak in one of my tires.
> The car is a 2002 Subaru Impreza TS with factory spec tires 195/60/R15.
> * Turns out the slow leak was due to a puncture in the sidewall of the
> tire, so that tire is garbage. *The tires are all about a year old and
> have decent meat on them, but the tech said you can't just replace one
> tire on an AWD car, you have to replace all 4 as a set, because the new
> one will be some sixteenths of an inch larger than all the rest.
>
> Of course he'd say that
>
because that's what FHI requires.

> Now, I understand the concept and theory of this- *if all wheels are the
> same circumference, they all rotate the same amount and internal
> drivetrain components (center diff or viscous clutch) don't have to take
> up the slack. *But... I have a hard time believing that an amount
> measured in sixteenths of an inch is significant. *Surely a few pounds
> of pressure off, or an unbalanced load (i.e., some fatass sitting in a
> seat opposite some 80 pound child) would make just as much difference?
>
> I declined to make any purchase at this time. *I know I'll need to
> replace that one tire, but I have another vehicle to drive for now. *I
> would like to replace the one tire only. *Replacing all 4 is a bit
> unnecessary, right?

That's what you'd like to believe. But it is does not make it right.
If it makes you feel better I see subarus and quattro outfitted audis
run on single axle brake force testing contraptions right and left.
(during annual technical "inspections" for example)

I never saw a gadget for testing brakes in a US of A auto shop,
not the one that spins two tires at the time (ruining awd hardware on
subarus).

I specifically do not buy a used subaru because of the cheapskates
like you:
one never knows what thew center diff was subjected to.

On Jan 10, 8:51*am, phaeton > wrote:
> Went to Firestone today because I have a slow leak in one of my tires.
> The car is a 2002 Subaru Impreza TS with factory spec tires 195/60/R15.
> * Turns out the slow leak was due to a puncture in the sidewall of the
> tire, so that tire is garbage. *The tires are all about a year old and
> have decent meat on them, but the tech said you can't just replace one
> tire on an AWD car, you have to replace all 4 as a set, because the new
> one will be some sixteenths of an inch larger than all the rest.
>
> Of course he'd say that
>
> Now, I understand the concept and theory of this- *if all wheels are the
> same circumference, they all rotate the same amount and internal
> drivetrain components (center diff or viscous clutch) don't have to take
> up the slack. *But... I have a hard time believing that an amount
> measured in sixteenths of an inch is significant. *Surely a few pounds
> of pressure off, or an unbalanced load (i.e., some fatass sitting in a
> seat opposite some 80 pound child) would make just as much difference?
>
> I declined to make any purchase at this time. *I know I'll need to
> replace that one tire, but I have another vehicle to drive for now. *I
> would like to replace the one tire only. *Replacing all 4 is a bit
> unnecessary, right?
>
> Thanks
>
> -J

I immediately thought of a guy here who run mismatched tires on front
and back axles of
a quattro audi (torsen based one, not haldex crap based one
obviously).

the drivetrain was making all sorts of noise to a point that snake oil
salesmen offered to ditch the driveshaft essentially converting the
car to fwd.

all the noise was gone once the guy had installed 4 matching tires
audi requires.

the drivetrain on subaru would've been probably ruined by the same
treatment
but torsen seem to take this kind of abuse better, or so i would like
to believe

phaeton wrote:
> Went to Firestone today because I have a slow leak in one of my tires.
> The car is a 2002 Subaru Impreza TS with factory spec tires 195/60/R15.
> Turns out the slow leak was due to a puncture in the sidewall of the
> tire, so that tire is garbage. The tires are all about a year old and
> have decent meat on them, but the tech said you can't just replace one
> tire on an AWD car, you have to replace all 4 as a set, because the new
> one will be some sixteenths of an inch larger than all the rest.
>
> Of course he'd say that
>
> Now, I understand the concept and theory of this- if all wheels are the
> same circumference, they all rotate the same amount and internal
> drivetrain components (center diff or viscous clutch) don't have to take
> up the slack. But... I have a hard time believing that an amount
> measured in sixteenths of an inch is significant. Surely a few pounds
> of pressure off, or an unbalanced load (i.e., some fatass sitting in a
> seat opposite some 80 pound child) would make just as much difference?
>
> I declined to make any purchase at this time. I know I'll need to
> replace that one tire, but I have another vehicle to drive for now. I
> would like to replace the one tire only. Replacing all 4 is a bit
> unnecessary, right?
>
> Thanks
>
> -J

With AWD you replace all 4 at the same time.

The "concept" is reality on an AWD vehicle.


--
Steve W.

On 1/10/2012 1:29 AM, Steve W. wrote:


>
> With AWD you replace all 4 at the same time.
>
> The "concept" is reality on an AWD vehicle.
>
>

Well then. It is what it is. Is it possible to buy a new tire and have
the tire shop shave the tread down to match the other three?

Wasteful as it is, it seems like a proper solution. Otherwise, I'll
replace all four.


Thanks.

-J

Have you considered fitting an inner tube to the tyre with the leak?


"phaeton" > wrote in message
...
> Went to Firestone today because I have a slow leak in one of my tires. The
> car is a 2002 Subaru Impreza TS with factory spec tires 195/60/R15. Turns
> out the slow leak was due to a puncture in the sidewall of the tire, so
> that tire is garbage. The tires are all about a year old and have decent
> meat on them, but the tech said you can't just replace one tire on an AWD
> car, you have to replace all 4 as a set, because the new one will be some
> sixteenths of an inch larger than all the rest.
>
> Of course he'd say that
>
> Now, I understand the concept and theory of this- if all wheels are the
> same circumference, they all rotate the same amount and internal
> drivetrain components (center diff or viscous clutch) don't have to take
> up the slack. But... I have a hard time believing that an amount measured
> in sixteenths of an inch is significant. Surely a few pounds of pressure
> off, or an unbalanced load (i.e., some fatass sitting in a seat opposite
> some 80 pound child) would make just as much difference?
>
> I declined to make any purchase at this time. I know I'll need to replace
> that one tire, but I have another vehicle to drive for now. I would like
> to replace the one tire only. Replacing all 4 is a bit unnecessary,
> right?
>
> Thanks
>
> -J

phaeton wrote:
> On 1/10/2012 1:29 AM, Steve W. wrote:
>
>
>> With AWD you replace all 4 at the same time.
>>
>> The "concept" is reality on an AWD vehicle.
>>
>>
>
> Well then. It is what it is. Is it possible to buy a new tire and have
> the tire shop shave the tread down to match the other three?
>
> Wasteful as it is, it seems like a proper solution. Otherwise, I'll
> replace all four.
>
>
> Thanks.
>
> -J

A good shop should be able to shave the tread. But finding a good shop
is a crap shoot some times.
If you can find one that does race tires or handles a lot of ricers you
would probably find a shaver that knew the work.


--
Steve W.

On Jan 10, 3:47*am, phaeton > wrote:
> On 1/10/2012 1:29 AM, Steve W. wrote:
>
>
>
> > With AWD you replace all 4 at the same time.
>
> > The "concept" is reality on an AWD vehicle.
>
> Well then. *It is what it is. *Is it possible to buy a new tire and have
> the tire shop shave the tread down to match the other three?
>
> Wasteful as it is, it seems like a proper solution. *Otherwise, I'll
> replace all four.
>
> Thanks.
>
> -J

Yes. But you'll probably have to find a race shop to do the shaving.
And they will refuse to do it once the tire has actually been operated
on the street (because the rubber of the tire tread will pick up
debris that will destroy the knife on their machine,) so you would
need to take the tire over to them in the trunk of another vehicle
(possibly with one of the old tires so they can measure the tread
depth on it with the same gauge that they're going to use when they
shave your new tire.)

Where are you? If you are in NoVA I can ask around, I have some
contacts that might know where to have this done.

good luck

nate

"AB" > wrote in message ...
> Have you considered fitting an inner tube to the tyre with the leak?

DING DING DING No more calls, we have a winner
with the obvious answer.

This practice was common once, years ago, but the
lemmings have since been easily convinced that they
need to replace the tire. Yes you'll get more heat buildup
but somehow I suspect you're not racing that greyhound
and that will never be the slightest issue for you.

On Jan 10, 1:51*am, phaeton > wrote:
> Replacing all 4 is a bit unnecessary, right?

"Here are recommendations from some of the manufactures that Tire Rack
currently serves for matching the tires used on their four-wheel drive
and all-wheel drive vehicles.

Subaru- Within 1/4-inch of tire circumference or about 2/32-inch of
each other in remaining tread depth."
http://www.tirerack.com/tires/tirete...jsp?techid=18&
-----

- gpsman