So I got a flat last night on my Subaru Outback, put on the spare and drove home. My wife took the car to the nearby Goodyear dealer this morning and he was trying to sell her 4 tires because he claimed that’s better for an AWD vehicle. I assume that in the grand scheme of things that is true, but my impression is that it doesn’t make that big a deal if the sizes all match.
So, my options are:
[ol]
[li]Buy 4 new tires - expensive and the other three tires still have life on them[/li][li]Buy 2 new tires that match the others - less expensive but the fronts/back will match side-to-side[/li][li]Buy 2 new tires of a different type - slightly less money but no real advantages othewise[/li][li]Buy 1 new tire that matches the others - cheapest option but I would rather have the same wear side-to-side[/li][/ol]
I generally favor option 2 but I’m open to any advice.
How much wear is on the tire on the opposite end of the axle?
If it’s more than half gone, I’d go with Option 2. If half or better remaining, Option 4.
ETA: A quick google reveals Subaru recommends nothing over 2/32" wear difference. Seems a bit conservative. Can you consult the owner’s manual?
I too, own an AWD car, and this just happened to me last month. As it was explained to me, the other 3 tires are worn to the point where they are smaller (in circumference) than the new tire they’re about to put on there. This will make issues for the AWD system as the computers (and mechanical differentials) get different input from one of the wheels relative to the other 3.
So, keep doing your research. Ultimately, it depends on the actual numbers. Did he tell you what the differences would be or just say, “Well, it’s our policy to XXXX.”? If the math shows you’re still within Subaru’s accepted specs for tire sizes on all 4 corners, then you should be okay replacing just the flat. But if the other 3 are significantly worn past Subaru’s specs, then you probably want all 4 to be new ones.
And this is Goodyear you’re dealing with, so they may have a liability issue with this, too. Alternatively, you could go to Joe-Bob’s tire shop, and they’d probably do whatever you want them to do. But don’t forget that it’s your AWD system in (potential) jeopardy.
The flat tire is supposedly beyond repair. I’m pretty sure I ended up driving it a few miles on the highway before noticing, so that’s not too surprising. The tires have approximately 25,000 miles on them, I think. I bought the car used and I’m checking with the previous owner.
I’m settling in on option 4 - 4 new tires. Not a planned expense but I’ll deal with it.
Note that not all AWD cars are made equal. With the part-time or partial power split AWD systems, you can get away with fudging the tire circumferences but it’s really asking for trouble on a Subaru or other full-time 50/50 AWD system.
How old/worn are the tires? If they’re still fairly new, the best option is to find a place that’ll shave the new tire down to match the other three. It may be a little tricky to find a place that’ll do it if you’re not in a place where Subarus are ubiquitous. The Subaru dealer might actually be the best bet for that.
If you have 3 tires with a lot of life on them, couldn’t you basically do the equivalent of the shaving down thing by looking for a used tire or pair of tires too ?
I checked with a Subaru dealer and was told that it’s important that all four tire diameters be within 2/32" of each other. Otherwise differential binding and possible damage may occur.
Another option is to buy one tire and have it shaved to match the others.
I’m going with option 4 - all new tires. It just wasn’t worth it to order a matching tire and shave it down for a set of tires I was going to replace at the end of the summer. They can put new tires on today so I’m going that route. Thanks for the advice everyone.
Correct. You may damage the AWD system if one tire is a different diameter than the others.
My Subaru dealer said they would actually try to keep used OEM tires in stock in order to help match, if possible. Not sure if that was true (possible liability issue of mounting used tires).
Supposedly, if really bad, a differential can overheat to the point of failure (best case), or combustion (worst case).
Yes, my owner’s manual (Nissan not Subaru) makes a big deal out of calling the spare a “TEMPORARY USE ONLY spare.” You’re supposed to use it to limp your car to the nearest place for service, not leave it on for hundreds of miles. With a full sized spare you’re supposed to include it in your rotation pattern so that the difference between the spare and the rest of the tires isn’t too great. My manual doesn’t say anything about pulling the fuse. For fwd vehicles and AWDs like mine where in non-slippery conditions the AWD is only active for a few moments and then it switches to fwd to save on gas, one might consider putting the spare on the back in the case of a flat on the front to make sure the tires on both drive wheels are good.
Oh, ok. The way everyone was talking about it, it sounded as if it would damage it somewhat immediately.
That’s interesting info. I’m curious if the MINI Countryman ALL4 is the same way (I don’t have the ALL4, just FWD), but I’m curious now. I’ll ask my dealer next time I’m over there.
