Do you really need 4 identical tires on a subaru AWD?

[leroy jenkins]

So went to get my summer tires put on, and they found a pretty good sidewall bubble in one. They tell me the tires are discontinued and they cant find any more.

They also tell me that because of the AWD (2000 outback) I can't put on one similar tire, it has to be identical. Of course, they're trying to sell me tires so, yea. I'm not too into that idea at the moment. A repair might last me the summer, but then again it might blow out, so I'd rather not do that.

So can I get away with something similar? What about two similar tires on the back wheels, and two of my existing tires on the front?

[scottishrider]

Have you looked for a matching tyre on ebay etc.? Thats what i did when i had sidewall damage on one of my legacy's tyres. While its not essential it is better for the diffs if the tyres have roughly the same amount of tread.

[mr_gyptian]

if you want your transfer case to last longer than 10000 miles.

[El Chupacabra]

While its not essential it is better for the diffs if the tyres have roughly the same amount of tread.

Also, if you're trying to match the circumference on the 3 old tires, new tires can be shaved down for a closer match. This is more of a race car thing, so you'll have to call around to find a shop that can do this for you.

[murph]

Been told the same thing when I blew a tire. Don't see why you couldn't just get two new for the front or back.

[coreshot-tourettes]

1 tire different diameter than others = diff and xfer case wear. To the diff and xfer case, it's like you're driving with one wheel always slipping. This is why it's very important to rotate tires on AWD vehicles and check tread depth.

[leroy jenkins]

Have you looked for a matching tyre on ebay etc.? Thats what i did when i had sidewall damage on one of my legacy's tyres. While its not essential it is better for the diffs if the tyres have roughly the same amount of tread.

Also, if you're trying to match the circumference on the 3 old tires, new tires can be shaved down for a closer match. This is more of a race car thing, so you'll have to call around to find a shop that can do this for you.

so is it just the size thats an issue? so i can get away ith something similar if i can get it shaved down? or at least a 2 and two, new and old?

if you want your transfer case to last longer than 10000 miles.

car's at 143k. Wil it just explode if I try this now? I hope not.

[theetruscan]

When the same thing happened on a 4wd volvo, no shop I could call would tell me it was ok to not have 4 identical tires. They all said, "your car will die."

[DropCliffsNotBombs]

The traction systems on Subarus and Audis are very sensitive to mismatched tire sizes. Nature of the beast.

[nickinbc]

How long do those diffs last if you live somewhere where the roads are rarely straight and have lots of tight curves? In some places I would have thought you would get FAR more wear on the diff from that than a slight difference in tire diameter.

[zombinate]

car's at 143k. Wil it just explode if I try this now? I hope not.

It will explode. And cause cancer. And have sex with your girlfriend. Just, ya know, FYI.

[El Chupacabra]

so is it just the size thats an issue? so i can get away ith something similar if i can get it shaved down? or at least a 2 and two, new and old?

It's the circumference, not width.

On a 4x4 (e.g. Jeep), some will use a skinnier spare tire to save weight and/or space -- for example, use 33x12" tires on the Jeep, but a 33x9 for the spare. The circumference is the same, more or less.

Caveat: I have never owned a Subaru or Audi; I have no idea if their AWD transfer cases are super fragile and really require very close tire sizes.

[Snow Dog]

Subaru has at least three AWD systems. They use some form of limited slip centre differential or viscous coupling so the wheels have to be the same diameter. Other AWD systems use an open centre differential and wheel size doesn't matter. They don't work as well either.

[leroy jenkins]

ok, so maybe i wasnt super clear.

I can get something the same width and get it shaved to the same circumference. However, since this particular model is discontinued, I can only get something with similar tread pattern, not exact.

So what will having one tire with different tread (not more tread) mean?


I guess I'll have to make sure the wear rate isn't too different, but other than that, what issues would i have, subaru related or otherwise?

[Obstruction]

Buy a used tire. Match the brand, tread and size. Most online used tire pimps will indicate how much wear the tire has they also claim to test them before selling and shipping. I've bought from these guys before to get a match (for an outback) http://www.bestusedtires.com/.

[moose pit]

Just make sure you have 4 matching rims

[uglymoney]

I guess I'll have to make sure the wear rate isn't too different, but other than that, what issues would i have, subaru related or otherwise?

If you have tires that have superior wet/snow grip on the front of the car the car will be very susceptible to uncontrolled oversteer in wet/snow conditions. The same would be true in dry conditions but most tires release a little slower on dry pavement so I doubt you'd have a problem.

So if you make sure to put the tires with the best grip on the back of the car, or if the new tire has essentially the same traction properties you'll be fine - as long as the diameter is the same. I think if you stick to the same brand of tire with the same general wear rating, you're probably getting similar rubber. I'd be more concerned with getting a very similar rubber compound than tread design.

I had a front drive Taurus SHO once that I had Potenza all seasons on the back and BFG HR4's on the front. The BFG's were such a superior tire in every condition that the car was completely uncontrollable on a slippery surface - it would swap ends in the blink of an eye even when you applied proper countersteer/throttle to try to correct it.

Even so ^^^ some people put snow tires only on the front of their FWD cars (with less grippy tires on the rear axle) and swear they can keep a handle on things. I'm not from that school of thought.

Good luck.

[uglymoney]

How long do those diffs last if you live somewhere where the roads are rarely straight and have lots of tight curves? In some places I would have thought you would get FAR more wear on the diff from that than a slight difference in tire diameter.

This has always been my train of thought. Though curves will be amplified when you have different sized tires. I had to replace the center diff on my MT5 Subaru at the cost of $1000 even though my tires have always been properly rotated and the same diameter. Sometimes they just shit the bed.

In another thread it was posted what the acceptable difference is. I think it's in the owners manual? Was it 2/32? I'd check but my car is in the garage and that is about 20 feet away.

[hutash]

Have you tried a google search to see if somebody, somewhere has one? I can't imagine there is not one setting in a shop somewhere with your name on it.

I would think that getting a similar tire (same hardness, temp rating etc.) would be adequate if shaved. That and rotating it frequently to keep wear even.

[Snow Dog]

ok, so maybe i wasnt super clear.

I can get something the same width and get it shaved to the same circumference. However, since this particular model is discontinued, I can only get something with similar tread pattern, not exact.

So what will having one tire with different tread (not more tread) mean?


I guess I'll have to make sure the wear rate isn't too different, but other than that, what issues would i have, subaru related or otherwise?

One different tire doesn't matter. Long ago Car & Driver did a performance test with a Corvette and it's space-saver spare. They were surprised to find no practical difference on the skidpad or track.

[Dexter Rutecki]

This has always been my train of thought. Though curves will be amplified when you have different sized tires. I had to replace the center diff on my MT5 Subaru at the cost of $1000 even though my tires have always been properly rotated and the same diameter. Sometimes they just shit the bed.

In another thread it was posted what the acceptable difference is. I think it's in the owners manual? Was it 2/32? I'd check but my car is in the garage and that is about 20 feet away.

Pretty sure 2/32 (why not 1/16?) is what the tire places will tell you is the maximum difference.

I really don't think driving on even the curviest roads (unless you're just driving in circles all the time) could come close to the difference in tire rotation caused by having tires of different diameters would be. It would be pretty easy to calculate what the percentage difference in tire rotation would be on a very tight turn vs. different sized tires.

[XXX-er]

its obvious the best solution is to buy a new car ...don't laugh I have done this

I pay more for a full service tire dealer with branches all over the country ,it doesnt matter which store I am dealing with I get the same type of customer service so my tire dealer would take those tires , keep them as spares to help travelers ,pro-rate the wear and I pay the diff on 4 new tires,if I lived down there I may be into going cheap BUT up here I have just used the full service too many times ...it works up here

it worked to my advantage last year when I needed 2 tires for a new ford pickup I was running a shuttle for some rafters,they are off in the wiilderness and I need to come up with 2 new truck tires to pick them up which would involve me spending hundreds of $ on the owners behalf without his approval IF there were any tires in town ... no tires in town but my dealer had a couple of used truck tires the same brand & size for 75 $

4 real snow tires is the only way to roll ,it doesnt matter if its condoms or tires ... rubber products are not the place to skimp

[jerr]

In NZ there are kite-loads of old subis with really high miles and ski bums only ever servicing them to get through the next 6 months. There are tire mis-matches for Africa and I've never heard of this being a problem. As hutash said; as long as you get a similar type of tire (same hardness, temp rating etc.) with similar wear (wrecking yard?) you're all good.

[farmer]

do you have a full size spare that is the same as the other 3? just get a new spare that is similar, and only rotate the other 4. from now on

[nickinbc]

Pretty sure 2/32 (why not 1/16?) is what the tire places will tell you is the maximum difference.

I really don't think driving on even the curviest roads (unless you're just driving in circles all the time) could come close to the difference in tire rotation caused by having tires of different diameters would be. It would be pretty easy to calculate what the percentage difference in tire rotation would be on a very tight turn vs. different sized tires.

Ok.

Lets say tire diameter 630mm on the right and 631.5mm on the left (i.e. about 1/16 inch difference). That is about a quarter of one percent difference in rotational speed between sides.

Lets say a MODERATELY tight turn has a radius of 100m (320 feet). Track of a car is about 1.5m. So the outside wheel is travelling 1.5 % further than the inside wheel - which means the same difference in rotational speeds. In other words equivalent to about a third of an inch difference in tire diameter.