Tire shaving

[Sean]

Got a question. We have summer and winter tires for Angela's WRX. This spring, when we took the winter tires off, one of them had a blown out side. Well, the guy said there was a "bubble" on the side in one of the front tires. Angela is pretty sure it happened when she hit a pot hole the size of Illinois without slowing down. So we need to get her a new tire. I'm assuming we shouldn't use the damaged tire.

I've heard that you can't just throw a new tire on an AWD car, it messes with the AWD and damages it. Can you shave tires? Is there an easier way than buying four new tires?

Any info is appreciated.

[PhL0aTeR]

hmmmm... You'd think there would be enough slip in the diffs to accommodate for the minute change in diameter. unless its a rally car with lockers or something. (obviously they wouldnt be locked on pavement)

I definitely wouldnt use the damaged tire, but i wouldnt have a problem putting a new one on if it were my vehicle.

[Nooch]

My roommate has a WRX hatchback and he had one of his tires slashed actually and just replaced it singly. We have a friend who's a Nissan tech and he claimed it wouldn't be an issue. FWIW.

[asp_125]

Most newer "smart" AWD systems compensate for slight differences in rotation speed. They are constantly monitoring slippage and adjust.

http://www.4x4abc.com/4WD101/diffautoAWD_AWD.html

[Ghost]

Having been in the industry, we got this question a lot. The official answer is any tread depth differences more than 2/32nd of an inch is considered too much. The change in rolling diameter means that the Symmetrical AWD of yoru Subaru will keep trying to compensate for what it thinks is a tire slippage problem since one wheel is effectively rotating faster than the other.

The solution is to get the new tire shaved to within 2/32nd of an inch of your current set (measure their tread depth with a feeler and match the one on the same axle as the new tire).

Tire Rack shaves tires for a nominal fee ($25 IIRC), and as they're the partner vendor for Subaru dealerships, they can arrange to have a shaved tire sent to the dealership you choose OR you can just order it directly from Tire Rack and have it sent to wherever you prefer.

As to local tire-shaving shops, check with Discount and/or Big-O, or the Tire Source in Boulder. I know a lot of Auto-Xers get their tires shaved since lower tread depth = faster times, and I'm pretty sure they use Discount if they don't just get them from TR.

Most newer "smart" AWD systems compensate for slight differences in rotation speed. They are constantly monitoring slippage and adjust.

Subaru and Audi both strongly recommend against it. Other manufacturers are less sensitive, but it's still never ideal.

[Penadam]

I believe the WRX uses a viscous coupling as the center diff. What can happen if you put a tire with a different diameter on is you will drive the center diff constantly, which in turn can drive an axle at a speed different than the road speed. It's not so bad with a viscous coupling as they always allow for some slip, but it's bad news for a mechanical coupling (torsion AWD for example). I think i've seen specs that recommend replacement if the diameter difference is more than 3/32.

[Sean]

Having been in the industry, we got this question a lot. The official answer is any tread depth differences more than 2/32nd of an inch is considered too much. The change in rolling diameter means that the Symmetrical AWD of yoru Subaru will keep trying to compensate for what it thinks is a tire slippage problem since one wheel is effectively rotating faster than the other.

The solution is to get the new tire shaved to within 2/32nd of an inch of your current set (measure their tread depth with a feeler and match the one on the same axle as the new tire).

Tire Rack shaves tires for a nominal fee ($25 IIRC), and as they're the partner vendor for Subaru dealerships, they can arrange to have a shaved tire sent to the dealership you choose OR you can just order it directly from Tire Rack and have it sent to wherever you prefer.

Thanks, that's what I've heard too. But I didn't know that Tire Rack shaves too and could even work with the dealership? Good to know.

[Ghost]

Thanks, that's what I've heard too. But I didn't know that Tire Rack shaves too and could even work with the dealership? Good to know.

Yep, TR will ship to the dealer, or you can have the dealer do it all.

FWIW, even the best dealerships can F things up, so I usually would call the dealership, tell them what's up, ask if I can have the tire shipped to them and have them arrange to call when it's in so you can come in and get it mounted.

Then, call TR and order the tire, have them shave it and ship it to Your Dealer. Since TR supplies all the tires for all the Subie dealerships, it's not a big deal at all for them. TR will ship the tire, the dealership will call, you go in, pay them to mount it, and you're done...

[Sean]

So far I have an email into Tire Rack to get a quote for the tire, shaving and shipping to dealership. Otherwise Big O is in the lead. $200 for a new tire (shaved I think) and installing three other tires. What a PITA!