Can you put only two new tires on an AWD?

[Tleg93]

I've heard no but I'm not convinced.

[vrg3]

You shouldn't.

It's been discussed in other threads, I think, but basically the AWD system wants both the front wheels and the rear wheels to rotate at nominally the same rate. Subaru's spec for acceptable circumference difference is ridiculously small, and you always cause speed differences whenever you turn the car, but... it's probably not something to risk.

It would be possible to replace just one tire on each end of the car and maintain the static speed ratio of unity. But then you'd probably sacrifice a lot in the way of handling.

My understanding is that with a 5MT a constant speed differential will eventually shear all the viscous fluid in the center differential, leaving you with an open diff, and with a 4EAT you'll start to experience something like torque bind.

[legacy92ej22t]

*cough, cough* [shamelessplug] I have a set of very nice Fulda tires that would fit your wheels for a very reasonable price. [/shamelessplug]

[elkaboom]

Isn't this more of an issue with later model AWD cars? Not that I make it a practice of mismatching wheels and/or tires but I'm more curious than anything else.

[93Leg-c]

creel: if when you say "two new tires" you mean two brand new, full tread depth new tires and the other two tires on your AWD are worn, I would say no.

But if when you say "new" meaning two new for the car tires but used and the same dimensions as the two worn tires on the car, then, maybe.

I had to face that very issue a couple of months ago. The treadwear indicators were just showing on two of my Michelins but the tread was cracking and the edges of the steel belts were coming through. Not the "Oh I see a little shiny stuff there" kind of coming through but how about 3/8 inch of the edge of the steel belts separated and sticking through the cracked tread!?!?!!

Because I could not afford new tires, or even four used tires I had no choice but to get two used tires. . . worn to almost the remaining two tires on my AWD. The result -- torque binding!!! I measured the ride height of the "new" tires and compared them with the two already on the car. The two "new" tires on the rear were almost 1/2 inch taller than the ones on the front (different brands have different dimensions though the same size tires).

So I put the taller tires in front, hoping the weight of the engine would compress the tire to a lower overall ride height and hoped the lighter weight of the rear would allow the other two tires to get a little taller. Result: almost exact same ride height (about 1/16 inch difference). And no torque binding!

Would I do it again or recommend it? Not if I can help it. I think it puts abnormal strain on the AWD system. Would I do it again if I had to? Only if I really, really had to . . . like I had to a couple of months ago.

BTW, I just put on 4 almost new WRX rims and tires on today so that ends the saga of the mis-matched tire set.

[BAC5.2]

Isn't this more of an issue with later model AWD cars? Not that I make it a practice of mismatching wheels and/or tires but I'm more curious than anything else.

No, it's an issue for ALL AWD cars.

All 4 tires should be the same make, model, size, and wear. Like Vikash said, the margin for error that Subaru allows is ridiculously small.

You shouldn't ever just get 2 new tires. I'm sure Matt would sell the Fulda's for a price that'd be more of a bargain than 2 new tires.

[entirelyturbo]

It doesn't matter what kind of 4WD system it is, on any car. AWD, locking 4WD, whatever. All 4 tires must be the same size, and the same wear. If not, you risk damaging the 4WD system.

My XT for example had 2 very bald tires on the front when I got it, and when I would use 4WD I could feel it slowing the car down as the back wheels were literally holding the front wheels up. And whenever I would shut 4WD off when moving, the whole car would jerk violently, because there is extra stress on the gears that was just released suddenly.

So yes, always buy tires 4 at a time, and rotate them on a very strict schedule.

[Noahdl88]

Funny story, i had 175s on the front of my DL when i got it and 185's on the back, it took flipping over to realize it. I did however pick up a nail yesterday in my legacy, put one new one on, the tire place said they had the tire, well its a completely different tire, but the same size, the other tires have about 3 months on them, so i'm not too worried yet, but i'm gonna keep an eye out

[BAC5.2]

Every company (and even models from a company) size differently.

My 225/45/17 Nitto's are smaller than a 225/45/17 Falken Azenis.