My parents have a 2017 Outback. The original tires have 36,000 miles and one just got a nail in the sidewall. Dad wants to change two of them but I remember that Subaru AWD is very sensitive to tire diameter.
Just how sensitive is it really? Will replacing two cause destruction?
Has Subaru moved to electronic application, or is it still some sort of clutch? In mechanical systems, there is a pretty small allowable difference in rolling diameter. Electronic control is a bit wider, because its smart enough to figure out you are not spinning two tires continuously.
Why not just replace one and have it shaved to match?
that will let him stretch the rest of the tires useful lives without risking the awd.
In reply to No Time : That’s a really good suggestion
I have done this twice on my Forester. I used Tire Rack, others can probably do this too. Just give them the required target diameter or tread depth and they will shave to your specs for a small fee. Way cheaper than buying a set of four, especially if your tires are only partly worn.
The allowable variance I want to say is no more than 3/32" (don't quote me on this--I'm thinking I read it somewhere). I run into this frequently with customers when we need to replace a damaged tire just like this case. They always want me to buy four tires for them but strangely balk when I suggest shaving down the needed tire to match the others.
I fail to see the logic in shaving a tire. 36K on the other 3, how much longer will they last? Then you have to throw away the shaved tire. Just get 4 new ones. Especially if you are in snow country, nice to have fresh rubber then.
Recently ran into this issue with my AWD CRV. I couldn't find any manufacturer recommendations for any AWD vehicles, just a bunch of tire salesmen trying to sell tires. I found someone that said 2.5% change in diameter was what was the manufacturer recommendation, but could verify that.
At 36k miles on the original set I'd probably think about replacing all 4.
I couldn't find anything in the factory service manual (of Subarus I've owned) regarding this specifically. The closest thing was a recommendation to change L and R tires as a pair if the tread depth of one is < 1.6mm.
Personally, at 36k I'd probably just replace all four as it wouldn't save much money to buy a single new tire now and replace all of them anyway when the remaining three wear down.
Streetwiseguy said:Has Subaru moved to electronic application, or is it still some sort of clutch? In mechanical systems, there is a pretty small allowable difference in rolling diameter. Electronic control is a bit wider, because its smart enough to figure out you are not spinning two tires continuously.
Automatic Trans = Electronic centre differential
Manual Trans = mechanical centre differential
Mine was driven (unintentionally) almost 80k miles with one 215 tire and 3 205s, and the original transmission still functioned at 450k when I swapped it for one with less miles because the input shaft bearings were so loose it sounded horrible. The differential still seemed fine though. Not recommending you do that, but its probably not going to immediately cause a major failure if things aren't quite right.
Agreed on the 36K replacement. I was just bringing up the shaving option for others who may have the same problem, but with lower mileage. With my Subie, my tires has less than 10,000 miles, so $185 for a new shaved tire, delivered to my door, was a whole lot cheaper than $700 for a full set, particularly when the other three were in great shape.
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