So I had a tire blowout that damage the rim. Bought a replacement rim, the tire installer said the tire was internally torn. They said that I'd have to replace all 4 tires or risk damaging the AWD.

I could potentially understand replacing an axle, but ALL 4? Any validity?

Pissing me off cause I have good tires with less than 10k miles on there.

 

MARKVIII, I agree that tires on the same axel should be replaced together. On both of my X-types '03 & '07 the front tires wore out faster then the back. So I never had all tires the same except the '03 when the car was brand new from the dealer. The '07 I bought used from the dealer and they replaced just the front tires at 29K miles. There was never a problem with AWD. Jack

 

So- your tire seller is trying to sell you tires? Imagine.

If your tires have less than 10K miles the difference in circumference between those and a new one is negligible.

 

Marc, what you need to look at is the difference in the tire circumference between the current tires and the new one. If you are within 1%, then you are golden. The system is designed to have a certain amount of speed mismatch between the tires (else you wouldn't be able to turn the car due to the tires turning in different arcs and therefore travelling at different speeds). You can check to see if you have too much of a difference by simply putting the new tire on the front and and then doing a hard acceleration. If the steering wheel wants to turn on you, probably need to replace both of the front tires.

But, I just did essentially the same thing you are looking at doing and I have had no issues. So, replace the one tire and enjoy the ride.

 

In theory, the installer is correct but it's not a simple rule that fits every AWD, each has different tolerances. You could jack up the car and use a taylors measuring tape to measure the difference in circumference between the old and new tire. The whole "only 10k miles on my tires" means nothing until you know their expected lifespan. I can only get 15k miles from the tires on my Corvette, so 10k is huge. Do you have soft grippy tires or hard "I want to kill myself in the name of cheapness" tires?

 

ONLY CHANGE THE 2 TIRES ON THE ONE AXLE!!!!! obviously this is a RARE event where you have totally destroyed a tire, so suck it up and buy both. it takes a good half-inch difference between the front and rears to confuse the AWD system. period.

 

As other have said, if your old tires aren't very worn, you're fine.

You have to understand how the AWD works. Keep in mind that with an AWD vehicle, everything is connected. If one tire is new, its got a larger circumference, thus rotates slower than a similar, more worn tire at the same speed. Something has to compensate for that. The good news is that the differentials and transfer case are designed to cope with a slight amount of variance. However, too much can cause a problem.

That said, I had the same thing happen. I lost my right rear tire at 70mph. It was destroyed. I rolled around for several weeks on one new tire and the three others were pretty worn. Was I way out of spec? Yes... Did it cause a problem in the limited time I did it? No... I needed to replace the tires soon anyway so I did. All is fine again.

Keep in mind that your tire guy wasnt trying to rip you off. He was following policy. When I replaced my one tire after my episode, I had to sign a release just to get them to put it on my car. They didnt want any liability if it DID damage the drivetrain.

If your tires are still close to new on the treadwear, you're fine. Just make sure the new tire that you choose is as close as possible in circumference as the others.

 

Does anyone know if the DSC could also be effected? It's "probably" not that sensitive but completely possible the DSC could start applying brakes and pulling power because of the variance between wheel speed. In theory, it all matters.

FYI, I used to have a Jeep and had to replace 1 tire and it would not disengage 4WD until I changed the other. It put just enough pressure on the transfer case that it wouldn't disengage. Put it on a lift and everything worked normal but on the ground, no dice.

 

be safe, not cheap. Buy 2 tires. if the 2 match on the same axle you will be fine. why risk running ONE awkward tire??? Especially when the cost of DSC and AWD components cost much more than tires? Again, not likely at all you will completely blow another tire and have to buy 2 at the same time again....

 

But then you have one axle set turning at a different speed than the other- what about that?

 

again, it is likely the disparity between the fronts and rears is much less than 0.5"

So it will in fact be just fine. The reason I would not want different sizes on the 'same' axle no matter WHAT the disparity, because it is hard on bushings and suspension components when cornering. It's unbalanced and I would personally not want that.
Same reason you are constantly told to rotate and balance your tires, as well as always keep your car in alignment.

 

Hey Mikey, you're kidding right? The difference in a couple of mm is nothing. The thing you're trying to avoid is called drive line wind up. You put 225 /60 on the back and 235/40 on the front. In a FWD or RWD you're fine, in an all wheel or 4 wheel drive you have the transfer case winding up because the 2 drive shafts (or transaxle and driveshaft) are going around at different speed and the TC blows up all over the road. But replacing 2 tires of the same size is fine.

 

Yes I am. If the difference on one axle would 'unacceptable', then a difference between front and rear axle (induced by putting two new tires on one end) would be just as 'unacceptable'.

If none of this not acceptable, then four new tires are indeed in order. Best change the spare too, just in case.

The shoot from the hip tales of doom I'm reading here are a bit much.

 

You would pretty much have to have the fronts running on the cords and the rears brand new to have an 'unacceptable' differencial.

 

I would allways try to have the same tread on all tires if i could. Not to suit the AWD but just to keep the car in balance during cornering and braking.
Over the years of owning Jaguars - especially V12's - I have found the tires very seldom wear evenly across the width of the tire or from tire to tire. For this reason alone I would consider replacing tires in pairs at the front and back.