Replacing one tire on a Subaru AWD?

[Steve Carlton]

I got my first flat in over 20 years yesterday on the freeway on a 2007 Subaru Legacy. Two dealers said if the circumference of the new tire isn't within 1/4" of the others, which have 9,000 miles on them, I need to replace all four tires. I know Roger Kraus Tires in Castro Valley has good tire shaving equipment and has done it for years, so any downside to shaving the new tire to match the tread depth of the other three? Another tire dealer I've dealt with for years says that's not advisable.

[9dreizig]

I have always wondered why a shaved tire wouldn't be the answer to the tire companyies always wanting to sell you 4 new ones..
Why do they say it's not advisable ? If it's the same tread pattern and diameter what's left?

[Joe Bob]

I have a four wheel "QUAD STEER" Yukon. I was having issues with the rear wheel sensors. The first thing they looked at was the tires. They checked the date codes and sizes. The tried to void my warranty because the tires were one size larger/taller than oem.

I HAD replaced all four but with the sizes it came with when I bought it, it was a demonstrator model, there was NO admonition to use a particular size in the manual. I brought this up in my negotiations to get a repair.

The second set replacements had close to 25K on them.....I had to yell and scream but they fixed it...next set of tires I went with the "stock" size.

[JayG]

With full time 4wd, it can cause premature wear on the transfer case and vibrations. Good tire shaving should work. I had a Galant VR4 and had to do the same thing. There are people that run staggered wheels on AWD cars and get alignments so they still have identical contact patches. Lot of work but saves on repairs in the future.

[Dave L]

Originally Posted by 9dreizig

I have always wondered why a shaved tire wouldn't be the answer to the tire companyies always wanting to sell you 4 new ones..
Why do they say it's not advisable ? If it's the same tread pattern and diameter what's left?

I think you answered your own question. Why would they recommend you buy one tire when they can recommend buying 4.

I cant see why you couldnt shave the new tire to match the other 3.

[Steve Carlton]

Originally Posted by 9dreizig

Why do they say it's not advisable ? If it's the same tread pattern and diameter what's left?

The answer seemed pretty lame to me. It was like the shaving process would remove tread evenly all around the tire, preserving any imperfections already there. I would think it would wear the same way normally, anyway. They also mentioned that it's a good idea to rotate the tires more often than the recommended 7,500 miles, as Subarus and Audis seem to be sensitive to tires of slightly different tread depth. Supposedly, there's been a lot of lawsuits on the issue. I could live with more frequent rotations to play it safe.

The place that shaves the tires said they've done it about 10 times on other cars with no issues. I'll have them measure the tread depth on the other 3 tires and have them shave the new one to the average. These tires seem to only be normally available at Subaru dealers, and few seem to carry them. The closest dealer I could find with them is 41 miles away, and I have to wait until Monday to buy the tire or get it shaved. Interestingly, the temporary spare doesn't have a speed restriction on the sidewall, but in the manual under "temporary spare" is says to not exceed 50 mph. Doesn't say anything under the tire changing section.

[supdaf]

I had a 95 Legacy Awd. Did it all the time. 160,000 miles later it got wadded up on the interstate. No problems. I did not like doing it but it worked for me.

[m21sniper]

They're just trying to sell you a full set of tires.

Tell him to STFU and sell you one tire before you simply go elsewhere.

[supdaf]

I started thinking about this thing and a couple of points started to stand out. Is the car standard or auto. Subaru uses different systems for each. The standard uses a viscous? coupling that heats up if wheels spin at different rpms. Mainly front to back. obviously they have taken care of turns where there is a bunch of differing rpms. The autos (what I have) use a computer that senses wheel spin and disengages a clutch in the tail of the tranny to engage the drive shaft, ie the rear wheels. I wonder how much of a difference in wheel speed causes the transmission computer to engage the rear? I do not know how a side-to-side difference effects the front two wheels. I believe from what I have studied that the system in the auto is not advanced enough to work side-to-side only front to back. Right now I have another 95 legacy that is basically full time awd. The wire to the solenoid to the transfer clutch (power to the rear) ohms out open. The system is fail safed to be awd unless the computer energizes the solenoid causing the rear to be free. A Subaru tech said I should not drive very far with my current broblem, that was 30k miles ago. No prob yet.

Golly gee wiz

[flashgordon13]

In theory you should replace all 4 tires, but in the real world it will make no difference if one tire is not exactly the same diameter as the others. Just ask what the manufacturing tolerance is on new tires and you'll get a blank stare. The truth is that even brand new tires are different diameters. That is why race teams have guys that spend hours measuring tires to match up sets that are close to the same sizes. I would just throw a new tire on the car and keep cruising.

[vash]

i had the exact issue come up. forester, stick shift. i asked the dealership mechanic. he said is a a real problem with tires that have lots of miles on them. we had a catastrophic failure at 1000 miles, so i just moved the spare into place, and put a new one as a spare. (brands were diff). no issues. on high mile tires, i would just change all four since the car is my wife's. i wouldnt want anything to happen. if it were mine, i would try changing just one.

[71T Targa]

I would think 5-10 PSI difference in tire pressure would have a bigger impact on the effective diameter of the tire then tread wear ever could.

Surely they account for that?

[vash]

or having a flat out in the middle of nowhere and having to install your new spare with the other three crappy bald tires...who knows?