AWD and Flat Tires
August 3, 2020 4:31 PM   Subscribe

I have read that if an all-wheel drive vehicle has a flat front tire, then a rear tire must be swapped to the front before then replacing the rear tire with the spare. Is this true of all all-wheel drive vehicles?

Background: We are considering replacing our current, quite old four-wheel drive vehicle with a new one capable of mild off-road travel and decent performance in light snow. Almost all of the vehicles that would fit our needs are all-wheel drive*, but this apparent flaw in changing a flat tire is pretty daunting, especially combined with the dire warning that if the three normal tires are worn very far that driving with a spare could quickly damage the (expensive) all-wheel drive system.

Bonus points if you can recommend an all-wheel drive vehicle that does not have this problem, has a ground clearance of at least 8 inches, and can tow at least 4500lbs. (Think Jeep Cherokee Trailhawk or similar.)

* I am aware that many vehicles marketed as 4WD are actually some version of AWD. In general only some trucks and Jeeps appear to be traditional four-wheel drive, which as far as I can tell does not suffer from this problem.
posted by jedicus to Travel & Transportation (8 answers total) 2 users marked this as a favorite
 
I'm not sure how to answer this question, because I haven't heard of a single car that requires swapping a rear tire to the front to change a spare.

AWD cars are generally sensitive to the diameter of tires. If one tire is smaller/larger than the others (for instance, a relatively unworn spare tire replaces severely worn normal tires, or if the spare tire is a different size than the normal tires), than the AWD system will stress the differential to try to normalize wheel speeds. However, that effect is not prominent in a typical 25-50 mile drive to a tire store to fix the normal tire. Further, that effect isn't fixed by doing a front/rear swap unless you've done a very poor job of rotating your tires.
posted by saeculorum at 5:06 PM on August 3, 2020 [3 favorites]


Have never heard this, have driven Foresters for years and haven't had an issue when we've had to drive on a spare. I do know you can't replace one tire with radials - need to replace at least in pairs iirc. Maybe I've been doing it wrong all along but haven't wrecked the car doing so yet.
posted by leslies at 5:32 PM on August 3, 2020


I'm not sure how to answer this question, because I haven't heard of a single car that requires swapping a rear tire to the front to change a spare.

Have never heard this, have driven Foresters for years

For example, the 2020 Forester Manual, page 422 [pdf]:
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.
posted by jedicus at 5:44 PM on August 3, 2020


That's if it is a temporary (smaller sized) spare tire. That would not be an issue if you had a full size spare.
posted by Dip Flash at 5:48 PM on August 3, 2020 [6 favorites]


I had a flat front in my 2018 Subaru WRX and the folks at the tire shop just popped the spare on where the flat was. Whether they SHOULD have moved a rear tire to the front first, I don't know, but they did not do that.
posted by Malleable at 6:13 PM on August 3, 2020


This is true of FWD as well, more so for handling issues.


AWD and 4WD use some computer technology to figure out when to activate the other wheels in specific ways to deal with traction issues, when you use the spare the computer system can malfunction and the car do things you are not quite expecting.

Get a full sized spare if this is a concern you have and you don't feel like changing two ties to deal with a smaller spare.
posted by AlexiaSky at 8:25 PM on August 3, 2020 [2 favorites]


I Have never heard of doing this, but it makes sense. I just looked at manuals for my '09 AWD Outback and my wife's FWD Lexus. Both have this warning. I suspect this has to do more with steering then the drive wheels. If I was driving a couple of miles on a dry road to get the tire repaired I might not worry about it, however if I had a long drive especially on a wet road I will make sure to move a good tire to the front.

Here is something I found on the subject:

Why you should avoid putting a spare tire on the front of a car

So why exactly is it important to avoid putting a spare on the front of a vehicle? Basically, it comes down to a few basic reasons. The first is that many vehicles actually weigh more in the front than in the rear. Second, your car relies heavily on your front tires for braking and if you have a doughnut spare instead of a full-size tire, you won’t be able to stop as quickly or as straight. The front tires are also what your car uses when it needs to turn (in most cars, at least) and this will be thrown off a bit by a doughnut spare. And finally, having two different sized tires in the front of your car could actually lead to further damage is driven enough.

You learn something everyday.
posted by tman99 at 12:18 PM on August 4, 2020


I drive an older Volvo with AWD (2001 XC70) and the manual just says: "When one or more tires is replaced, the new tire(s) should be mounted on the front wheels. The tires with the least amount of tread should be mounted on the rear wheels." The spare tire is full diameter.

Also note that AWD systems vary a lot. It's my understanding that Subaru's AWD treats all wheels more or less equally, while Volvo uses a Haldex differential system that behaves like a FWD car until the rear wheels start slipping.
posted by neckro23 at 1:02 PM on August 4, 2020


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