Tire question

I was wondering if one tire had more tread than the other three would that compromise the awd in any way? I was going to purchase a set of snow tires from a guy that has a set of tires. One which is brand new and the other three that have about 90% tread. I appreciate your opinions.

Thanks

Steve

Forget the guessing and get a depth gauge and measure them. A big mismatch will cause more damage than a new set of tires.

Find out from Subaru what is OK to run. My .02

Subaru requires all 4 tires to have the same degree of wear:

http://www.subaru.com/owners/resource-center/vehicle-care-tips/article.html?uri=/owners/resource-center/vehicle_care_tips/posts/04082011_0000/&tq=posts/vehicle-care-tips

For safe vehicle operation, SUBARU recommends replacing all four tires at the same time. WARNING: All four tires must be the same in terms of manufacturer, brand (tread pattern), construction, degree of wear, speed symbol, load index and size. Mixing tires of different types, sizes or degrees of wear can result in damage to the vehicle's power train. Use of different types or sizes of tires can also dangerously reduce controllability and braking performance and can lead to an accident. Use only radial tires. Do not use radial tires together with belted bias tires and/or bias-ply tires. Doing so can dangerously reduce controllability which can result in an accident.

Subaru's official recommendation on circumference difference (1/4") comes down to about 3/64nds of thread depth difference. There is probably some safety margin in there somewhere, so depending on what exactly is 90% new (any my how much did the seller lie) - you might be okay. Basically if new are @12/32nds, and used one is at 11/32nds I'd say you're okay.

Subaru retracted that "official" statement several years ago. The new, official, statement is what I posted above.

Any difference in degree of wear has the potential for permanent drivetrain damage. All 4 tires need to be the same.

Subaru retracted that "official" statement several years ago. The new, official, statement is what I posted above.

 

Any difference in degree of wear has the potential for permanent drivetrain damage. All 4 tires need to be the same.

Latest "official" word is probably written by overly zealous lawyers. In reality 1/32nds is probably safe, especially for non-STI/spec.b.

If one is under warranty - I'd probably keep the wear equal. Otherwise I'd ran it if the price is good.

Latest "official" word is probably written by overly zealous lawyers. In reality 1/32nds is probably safe, especially for non-STI/spec.b.

If one is under warranty - I'd probably keep the wear equal. Otherwise I'd ran it if the price is good.

Neither the Spec-B, nor the STI, are more sensitive to different diameters than any other MT or 5EAT Subaru.

If you want to make sure you won't have a problem, make sure all 4 tires are the same exact diameter.

Period.

Neither the Spec-B, nor the STI, are more sensitive to different diameters than any other MT or 5EAT Subaru.

 

If you want to make sure you won't have a problem, make sure all 4 tires are the same exact diameter.

 

Period.

Of course they are different, since they have different diffs.

As for your 'period' - I have no time to argue with nonsense. No four tires will have EXACTLY the same circumference.

Of course they are different, since they have different diffs.

 

As for your 'period' - I have no time to argue with nonsense. No four tires will have EXACTLY the same circumference.

The Spec-B has a viscous center diff, open front diff, and a viscous rear LSD. Absolutely no different than the 5MT in any Subaru. The STI's DCCD is no more or less sensitive to damage from different tire sizes than the viscous diffs or the diff in the automatics.

As for my "period", you better believe that ALL tires of the same make/model/size are going to be closer than 1/4" circumference.

I have no time to argue with someone who doesn't know what they are talking about.

^the 07-09 spec b has the torsen R180 rear LSD.

That would actually make the 07-09 Spec-B slightly less sensitive to tire size differences, then.

A VLSD will catastrophically fail with a long slip duration (the fluid will shear, break down, overheat, and the plates will either weld themselves together or the housing will burst apart). Regardless of input torque, you will ALWAYS be ruining the diff.

A torsen-type unit will simply freewheel the planets when no torque is applied to the diff, and will attempt to speed up the slow tire when there is a torque applied. You'll notice the car handling funny before any real damage can occur.