We recently had a flat on our 2003 Subaru Outback that could not be fixed. We replaced the flat tire, but the mechanic was not happy about that, as he wanted us to replace all 4 tires. We were not able to replace all four at the time. Is it imperative that we replace all tires at once? I hear different opinions, from “it won’t be a big deal because the Outback only uses the all wheel drive when it detects that it is necessary” to “we will destroy the transmission if we don’t get new tires now.” Anyone have some accurate information on this? Should we really try to get new tires on the car, or is this just a ploy to sell more tires? Thanks!
How many miles on the old tire? How worn?
I would say they are about 12-14 months old. Probably around 15,000 -,18,000.
Read the owner’s manual about tires and the tolerance allowed. The measurement is circumference with a steel tape. Measure the new tire with a steel tape in center of tire, and then measure the tire that has the least tread on it. If that difference is within the allowed tolerance, you are OK. It it isn’t you need to replace the other tires with same brand and tread pattern. There are also instructions on how to put in a fuse and place the vehicle in FWD only mode. It is usually used when you use a compact spare, but it can be used in this case where the new tire may not be inside the Subaru specified tolerance.
There are cases where folks do have drive train damage by not staying with the Subaru tolerance. Note that a drive train repair is far more expensive than a four tire replacement. This is one of the known costs with AWD ownership, especially on Subarus.
You might also be able to get the tire shaved down to meet the standard. Read all the owner’s manual info and then decide what you need/can do to mitigate the costs.
I second what jahhawkroy said - read the owner’s manual. Think about it this way: if the tire is a slightly different size, it will rotate at a slightly different speed from the other tires. This means the AWD stuff (very scientific automotive term, I know) has to adjust to this difference all the time, not just every now and then. Buy the four tires - the repairs to the automatic transmission will cost you twice as much.
15-18k is substantial wear.
No ploy to sell more tires, Subaru’s have an incredible AWD system that is quite simple. However its major weak point is requiring matched tires. 15k-18k of wear falls outside of matched tires.
Your owner’s manual should cover this. Do you disagree with what it says?
“it won’t be a big deal because the Outback only uses the all wheel drive when it detects that it is necessary”"
Please ignore the advice from whoever told you that gem, because it is absolutely untrue.
If we were talking about…let’s say…a Honda CR-V or a Toyota Rav-4, whose rear wheels only have power directed to them when slippage is detected, that statement would be accurate. However, with a Subaru, it is dangerously false information. While the torque split varies from one Subaru model to another (some are 50-50, some are 45-55), you have power directed to all 4 wheels all the time.
As a result of that constant AWD, using tires that are not closely matched in terms of tread wear will put undue strain and wear on the AWD mechanism, and will result in expensive repairs. And, 15k-18k of tread wear vs a new tire is NOT a close match in terms of tread wear. Not even close.
So–your only choices are:
Replace the other 3 tires, a.s.a.p.
or
Have that one new tire “shaved” to match the tread depth of the 3 older tires. Not that many tire shops have the equipment to “shave” tires, but a few minutes with the Yellow Pages, followed by some phone calls, should yield the name of a tire dealer who can help you. Just be prepared to potentially drive a few miles to get to one of these fairly rare tire dealers.
Your mechanic was right, and so is the information in the Owner’s Manual regarding the importance of “matched tires”. Failure to heed valid advice will have a big price tag, so I urge you to take one of the two actions that I described above, and to do it VERY soon. Generally speaking, more than a couple of hundred miles of driving with this type of mis-match is enough to do major damage to the AWD mechanism,
You are risking damage to very expensive components of the AWD system. In addition to the transmission there is a transfer case that moves power where it is needed. One tire rolling at a different rate than the others will damage the system, the repair is several thousand dollars.
You can have the new tire “shaved” down to the same depth of tread as the other 3, or buy 3 new exact match tires. This is one of the downsides of AWD. If you don’t like buying all the tires at once you might not want AWD on future cars. IF you really must have AWD, then this is part of the price you pay for having AWD.
At the very least, you should replace both tires on the same axle. And. only if you are lucky enough otherwise to find the exact same size. make and model tire, and have taken the tread depth measurements. If the difference is 2/32 inch or less, from what I have read, you’re in luck.
Put the the newer tires ON FRONT as this difference is not significant enough to cause a traction difference problem. It’s within normal rotation wear regardless and your Subaru can handle it.
Keep track of wear on both front and rear as the fronts should wear faster. Then rotate when appropriate.
If the tires match exactly, but are beyond 3/32 difference…you be “skewed” and should buy 4 new tires…exactly the same.
VDC is exactly right as a Subaru uses awd, all the time, but varies the torque to each axle constantly according to driving demands, often having little to do with traction and more with accelerating, climbing and cornering forces and seldom remains constant.
This “replace all 4” any time idea is a CYA advice because it assumes many people don’t rotate their tires enough, carry the proper air pressure and carry a cheap tire tread gauge and USE IT. The idea of shaving is only to get tires within about 2/32 inch and not to match them perfectly…heck, the don’t when they are In use a year anyway.