Subaru AWD and a spare tire

Hey All,

I wanted to get all of your advice on the best way to handle a subaru vehicle with AWD should I ever get a flat tire? This comes after we just had to replace a costly brand new tire on my wife’s Acura TSX due to a sidewall puncture.

I do know that if there were my Subaru, I would have to get 4 brand new tires as they wouldn’t be the same in treadwear otherwise.

I have a cargo mat, along with a a bunch of stuff in my trunk. Does my 2012 Subaru Legacy even have a spare tire (I know, I should know this). However, if I, or someone else were to get a flat tire with a Subaru, how do you proceed? Would I want to just pay road side assistance to tow my vehicle to make sure that I don’t do any damage to the AWD system?

I would really appreciate all of your advice. Thanks much!

Use the spare (you probably have a donut spare) and limit the miles until you get it replaced to 50 miles. (I have a forester, and, strangely, there is not a limit on miles with the dount). A few miles like this will do no measurable damage.

Then repair the tire if you can. If you can’t, you have to look at tread wear and decide if you need to replace just the one, or replace all four. I don’t know the max difference in circumference allowed, but the tire store should know. Obviously it’s not zero, as all tires have slightly different circumferences even when new.

In theory you could buy one new tire and have it shaved down to match the other three, but I don’t know of any stores that offer that service.


PS, also limit the speed with the donut spare to 50 MPH. This should be in your manual.

Bill Russell has provided some excellent advice, but I want to add three important points for the OP to consider:

Do NOT have your car towed, unless you want to cause severe damage to the AWD system that would not be covered by warranty. If an AWD vehicle such as yours needs to be transported, it must be done with a flat-bed vehicle transporter. If you are ever in need of “a tow”, make sure that you specify in your call for assistance that your vehicle has AWD and cannot be towed.

Yes, you should know whether or not your vehicle has a spare tire, and doing this simply means picking up that trunk mat. When you do that–and find that your car does indeed have a spare tire–consider that unless you regularly check the pressure in that spare tire, it may be essentially useless when you need to use it. Somebody who wants to maintain his/her car properly will check the pressure in his/her tires–including the spare–on a regular basis. Note that the donut spare takes considerably higher pressure than the other tires–possibly as much as 60 psi.

Reading the Owner’s Manual that came with your car is very important, as it contains a wealth of information one the operation of your vehicle–including such things as the aforementioned prohibition on towing. If you take some time to read that manual (including the maintenance schedule which is contained in a separate booklet), your car will last longer, it will cost you much less to maintain and repair in the long run, and you and your passengers will be safer.

Yes, VDCdriver is correct, RTFM. (Read The xxxx Manual)

You can find a PDF version online if you prefer to read it on your computer.


I think there may be some specific instructions in the manual, including a fuse to pul in some cases. Check it out

" including a fuse to pull in some cases. "

I think you are referring to the practice with older Subarus, regarding the insertion of a fuse into a dedicated fuse holder (located near the right-side shock tower) in order to convert from AWD to FWD. However, that is no longer true, given the different nature of their newer AWD systems.

Guys. Did the OP ask to be lectured about reading the manual?

Or did the OP ask: " However, if I, or someone else were to get a flat tire with a Subaru, how do you proceed? Would I want to just pay road side assistance to tow my vehicle to make sure that I don’t do any damage to the AWD system?"

It’s wishful thinking to believe that the majority of the public reads the 600+ page owners manuals. Lecturing those who come here asking for genuine help contributes to them never returning.

Sure. I would love to see everyone read owners manuals. But we’re not going to change that.

Joe, you are correct, I apologize.

In fact, I have not completely read my 600 page manual. It is not easy to read.

ONE IMPORTANT POINT: (from the Forester manual)
The temporary spare tire must be used only on a rear wheel. If a front wheel tire gets punctured, replace the wheel with a rear wheel and install the temporary spare tire in place of the removed rear wheel.

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Joe, I don’t want the OP to sit down for hours to read the whole thing. But read the instructions for a flat tire? Definitely!

Tire Rack can shave a tire to match the others, so keep that in mind. Obviously that only makes financial sense if the other three tires are still decent.

If you did end up replacing all four tires, I’d keep one, as possibly it would be the right tread depth if another tire is needed in the future (assuming it wasn’t too old at that point).

It puzzles me as to why Subaru hasn’t designed a coupling system more tolerant of wheels of different sizes. It would seem that doing so would eliminate the concern that I suspect has an adverse effect on sales.

Mountainbike: Is it just Subaru or all makes with AWD? If it’s just Subaru, I would wonder what the difference is…

For my own reference, does anyone have a spec on circumference difference allowed? Manual doesn’t say anything… Obviously it can’t be zero…


"… I suspect has an adverse effect on sales. "

Actually, they have a problem keeping up with demand.
In 2013, they announced an expansion of their Indiana assembly plant in order to keep up with the anticipated demand, and in fact, their sales figures have continued to increase since then. As soon as they complete the expansion of that factory, they will cease production of Camrys there, as they need the capacity currently taken up by assembling cars for Toyota.

Here are two articles–one from 2013, and a very recent one:

When someone admits that they are too lazy to unload the cargo area to see if they have a spare tire of any kind no apology is needed for telling them to read the manual.

Kind of a stupid question in regards to the current post, but how does it work with the AWD and an automatic car wash (the one that you put it in neutral and it pushes you through? It seems like everyone takes AWD cars through them, but would the read difference be between that and towing a vehicle at low speeds?

The speed in an automatic car wash is usually ~ 1 mph.
Additionally, the distance involved is extremely short.

As a result of both of those factors, being pulled through a car wash cannot be compared to towing a vehicle at a speed of (probably) over 25 mph, and for a distance of…at least a few miles.

In a car wash, all 4 wheels are on the ground and moving at the same speed, so there is no problem.

Subaru allows two methods of towing,

  1. Using a flat-bed truck
  2. Towing with all wheels on the ground

Bill, I don’t know the answer. It seems like the issue always comes up when discussing Subie tires, but that may be because the overwhelming majority of AWDs out there are Subies.

If one were to put a slightly different diameter on each end of a standard differential, which is designed to transfer torque to both ends of the axle while still accommodating different turning speeds, there might be a slight difference in the differential’s life, which rarely is less than the vehicles anyway. It seems like Subie transfer cases (more specifically the internals) could also be designed to accommodate variations in speed sufficient to at least accommodate tire wear.

Perhaps I don’t understand exactly what fails. And why. Is the cooling of the transfer case assembly insufficient?

found this at

Some vehicle manufacturers recommend that all tires maintain the same rolling radius and circumference, while others suggest that all tire circumferences remain within 1/4- to 1/2-inch of each other. Other vehicle manufacturers recommend that all four tires remain within 2/32-, 3/32- or 4/32-inch of each other, or within 30% of each other in relative remaining tread depth.

Here are recommendations from some of the manufactures that Tire Rack currently serves for matching the tires used on their four-wheel drive and all-wheel drive vehicles. Additional recommendations from other Original Equipment Vehicle Manufacturers is pending.

Audi As published in their vehicle owner’s manual, “rolling radius of all 4 tires must remain the same” or within 4/32-inch of each other in remaining tread depth.
Porsche Cayenne within 30% of the other tire on the same axle’s remaining treadwear.
Subaru Within 1/4-inch of tire circumference or about 2/32-inch of each other in remaining tread depth.

To clear up confusion …

Some of the posts give very incorrect information about towing vehicles with the wheels down (called “flat towing”). Flat towing can damage many vehicles, so don’t buy a car you think can be flat-towed only to find out (the hard way) that it cannot. Other relevant issues include protection from gravel for the towed vehicle, suspension wear from the coupling assembly (not to mention whether you can fit a coupling assembly onto your particular vehicle), and auxiliary braking systems (for example, Ford says it’s OK to flat tow an older Escape hybrid, but NOT to use certain auxiliary brake systems).

It’s a complicated issue so rather than rely on a website, I’d recommend talking with a knowledgeable motor home source, and checking manufacturer data and aftermarket sources (like motorhome journals). If you key in Motor Home or flat towing, you can find manufacturer’s recommendations for many vehicles. Motor Home also has data for used vehicles, which may come in handy.

We lived in a motor home for a year and a half after I retired and flat towing is a good idea if you have a large and heavy motor home and want something you can use for errands and sightseeing while the RV is parked.