Replacing a tire on 2005 Subaru Outback

will buying one new tire for my 2005 suby outback cause me any trouble with the all wheel drive?

Yes it will. Subaru’s are very sensitive to tire diameter and one new tire with 3 older tires will cause harm to the AWD system.


I wish I was able to change all tires but I’m 200 miles from home and had a blowout. Cannot buy 3 more tires will have to make it home and measure the difference. And hope it’s not too far apart thanks

I know a person who ruined a Subaru transmission running mismatched tires, though it took longer than 200mi. Subaru forums mention a Subaru internal bulletin stating that tire circumferences should fall within a span of 1/4in., this translates to an ~ 3/32 inch range in tread depth but only if the circumference beneath the tread is the same, which it sometimes is not. Personally, I wouldn’t take the risk but if you must drive on one new tire keep the speed down.

Measuring circumference is easier with a flat measuring tape (Google them). Sewing/gluing/stapling two fiberglass fabric (no stretch) sewing tapes with millimeter graduations is one way to make one that’s long enough. Screen for size match when purchasing new tires and I check at each rotation - though well aligned and balanced I see different wear at each corner and rotate to keep the size range within limits.

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You may save a few hundred dollars now and cost thousands later when the differential dies. I wouldn’t do it.

Ask the tire shop if they can shave the new tire down to match the other three.

Depends on the difference in tread depth between the new and old tires.

If they’re within 1 or 2 32nds of each other it should be no issue.


Assuming they’re the same brand and model.

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It doesn’t matter the brand/make of tire.

If it were true? I’d never buy a Subaru.


Doesn’t Subaru provide a way to disable the rear wheel drive for temporary situations? That would save your centre differential for the 200 mile trip.

That article mentions nothing about tread depth,

It does mention tire circumference being within 1/2 inch. Using circumference tread depth does not matter, you can run a bald tire and a brand new tire as long as the circumference is within 1/2 inch.

I got tires for the back end so that may help and trip home will be slower thanks for all your advice!

Boy would that be great! If only there was a button!!

That used to exist on their older models, but that capability was eliminated when they updated their drive system. I don’t recall exactly when that changeover took place, but I think that it was circa 2003-2004.

There was never a button. The procedure for disabling the AWD on older Outbacks involved inserting a fuse into a dedicated fuse holder that was mounted on the passenger-side front shock tower. If your car has this disabling capability, there will be specific instructions in the Owner’s Manual. In the meantime, take a look around the passenger side front shock tower to see if there is an isolated fuse compartment. If there is one, then you have the capability of disabling the AWD.

I couldn’t load your post, sorry, what’s the url? Various Subaru user forums claim 1/4in. for Subarus traceable to a Subaru factory publication and a tire factory rep. confirmed this, many other mfgrs spec. 1/2in. but their AWD systems differ from Subaru’s. My experience: purchased a set of 4 new tires in a hurry last summer after one was damaged while traveling away from home. Shortly thereafter I measured the circumferences with a flat metal tape graduated in millimeters and found one that was 7mm larger than the others, measurement repeated several times. All tires were same mfgr, model, and date code but the larger one had a different tooling number meaning it was from a different mold. The other tires were within 1-2mm. Would expect that other mfgr’s tires could vary more and with variances in construction details may have different relationships between static and rolling circumference, but would need direct data to know for sure.

Was told by a Subaru mechanic that tire rpm data is available at the ODB port (true?), would make for an interesting experiment - variables could be tire manufacturer and inflation.

How many miles do you have on the original three tires?

I’m thinking too many but am going to measure front and back wheels

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my guess is that a few hundred miles will be ok. But keep the speed low.

This is based on the Subaru manual for the spare tire, which is very much of a different size, and they put no limit on mileage with it, just a 50 MPH speed limit. Although I think the lack of a mileage limit is a mistake, other manufacturers all spec that, as far as I know.

It’s too late now, but keep in mind for the future that Tire Rack can shave a tire and deliver it to you quickly if needed.

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There may be a label that states the ’ donut ’ spare tire has a 50 mile limit or it could be in the manual.

Thanks will go slow. Nice empty place on the dash for the all wheel drive button. :grinning: