Learn Me Some AWD Tires

[SentraWV]

OK, the girlfriend has a 2003 Legacy sedan and is in need of a couple of new tires to pass inspection this month. The guy at the place in Pitt from which she has a gift card (Flynn's, IIRC) says she has to get four new ones, not two, because it's super important that all the tires be the same on an AWD car.

To me, this suspiciously sounds like somebody trying to sell two more tires. If the fronts are the same and the rears are the same tire (and all the same size) would that be a problem?

Thanks!

NP: Marillion, Somewhere In London (DVD)

[gtfour77]

Ideally you'd want to have 4 of the same tires with same wear and same diameter. A tire that is 50 -80% worn will have quite a bit different diameter compared to a new tire. IF the two good tires are still very good (meaning have more than 60 or 70% tread remaining) I'd only get two tires. You want the same diameter to keep all the diffs happy.

[Hillbilly]

What Marteen said. Gotta be the same size on all four corners of the car or the diffs are constantly slipping and getting hot and wearing out faster.

[TimMaddox]

Not sure about tires, but a wife has a 2003 Legacy sedan. A girlfriend has a 2003 Corvette.

[SentraWV]

I understand the size needs to be the same on all fours - they are and will be. My question is whether the specific tire brand/make needs to be the same. In other words, if the fronts are Falkens and the rears are Kuhmos, all of the same size, does it matter?

Tim - she couldn't have a better car than I do, could she? :wink:

[AchTTung]

The diameters being within spec would be the important thing, but having them be the same brand would be the easiest way to ensure that, I suppose. : )

[Kurt_W]

As others have said, ideally you would have 4 of the same brand to insure matching diameters and wear patterns. Alternatively if the car has 2 tires with significantly more tread left (enough to make them worth saving) you could get 2 matching tires and have them "trued/shaved" to match the tread depths.

Friends don't let friends drive Neons. ;)

[crobin4]

Yes, they should be the exact same tires. The center diff will only tolerate ~1/8" difference in rolling radius F/R. If you look at alot of tire specs, you will see that all tires of the same size a not always exactly the same diameter. This also means one stay on top of tire inflation. This also, effects the rolling radius of the tire. This is not to say the diff will fail immediately, but it does cause a significant amout of wear and will drastically decrease the life of the Cdiff.

[gtfour77]

If you look at alot of tire specs, you will see that all tires of the same size a not always exactly the same diameter. This also means one stay on top of tire inflation.

Excellent points Chris! Jon, many manufacturers use their own "specs" for tires. (insert sarcastic joke here as we all know how the sticky tire business works where the same tire size from one manuf. can be almost an inch wider than the other's) I'd stick with the same brand/model tires on all four corners unless you can make absolutelly sure that the rolling diameter is the same on all of them. And then you also want to make sure you have the same or at least close tread wear rating on those two tires...

[SentraWV]

Thanks, guys. Not the answer I (or she) wanted to hear, but that's the way it is. I've seen the spec variance issue come up in discussions of stickiness, but not so much sizes. I'm amazed, in the highly regulated 21st Century, that such things aren't more uniform.

Oh well.

[TimMaddox]

I have run different tires on a two wheel drive beater pickup, but I don't think I would try it on all wheel drive. In addition to diameter, I also think that the tire compound, speed rating and performance level should be similar if you are going to try it. You wouldn't want to run Sears Road Handler snow tires up front and Kuhmo V710s in the back, it might make the back end stick too much.

...which gives me an idea for the Neon's autocross set up...