Bearclaw

Here's a good one, and by "good" I mean "awful". I had a puncture on the road, the tires were aged anyway, so I bought a new set. Continental Contact Contol's. I drive home 25 miles, drive around a bit, and think "these tires suck". I call the tire store and tell them as much. We decide on a new brand/model. I'm on my way back to the tire store, and I realize the car's acting weird and the AWD light (this is a '91 C4 ) is activating intermittently. I stop at my office and look at the tires, and sure enough - the fronts are 205/50-16's instead of 55 aspect ratio. So it's really pissing off my AWD. I looked it up, and the dia. difference is about 3.2%. I'm about 2 miles from the tire store, so I'm headed there now. I figure, whatever is gonna happen has already happened.
So, to recap:
Dumbass tire store for fitting wrong tires (they had the correct ones on the bill, but shop guys hosed it up, I guess).
Dumbass car owner for not checking this at the first sign of abnormality.

So what's the damage here? Whatever it is, they're on the hook for it.

Rocket Rob

The rolling diameter is definitely off. Having 205/50 tires would have put extra stress (wear) on the center diff. Is there damage? I hope not. I would be inclined to change the tranny fluid, if you want to be extra cautious.

I've driven using my spare twice. Both times on the rear. I wonder how close to the correct rolling diameter that is? I'm guessing its close if not perfect because I never had an error light.

Keep us posted.

Streetdaddy

Mine are 225/40x17 and 205/50x17 on the front. That makes them 25.1 and 24.1 diameters. I just bought the car and the tires are 1 year old. Is this enough difference to scrap the tires and buy new ones?

BHCfarkas

Honestly, there isn't going to be any damage. There's enough play in just about every single car that you can get away with 5% difference without hurting anything. The only reason your light is coming on, is because your traction control is getting different readings from the ABS sensors and occasionally triggering the light. Essentially it sees your front wheels are moving faster than your rear and lets you know.

I would get the correct size and not think twice about it.

Streetdaddy

I bit the bullet and ordered the correct size.(205/50zr17...255/40zr17)

Previous owner had wrong size on there. Now what to do with like new tires?

Strega(UK)

I ran with wrong tyre sizes a few years back and it did cost me the diff! Being paranoid I now keep a spare gearbox just in case, as it was an expensive mistake to make!

BHCfarkas

How big of a difference were you running?

Navaros911

And I thought we only needed a spare DME relay... what else do I need in the glove box?

Strega(UK)

Was a few years back now, so sadly can not remember.