carfan1111

So I have a set of 4 bridgestone all season tires. due to my terrible driving, I ripped one tire after i hit the sidewalk. 3 tires are good and they are 8/32 (probably put 10k miles on them). When the car came, it had continental tires. When I replaced the tires, I kept one Continental tire (it also is 8/32).

can I put this continental tire on, or should I buy another bridgestone tire? if I put it on, what is the risk?

bridgestone tire:

Bridgestone Dueler H/L 422 Ecopia

continental tire:
Continental CrossContact LX Sport

they appear to have similar tire pattern

uberwgn

You shouldn't be mixing tires on these cars.


BTW, you'll likely find the correct (used ) tire on eBay or the like. Tire Rack can shave a tire for you.

superswiss

Quattro requires that you use 4 of the same tires (same size, thread pattern etc.) with thread depth within 4/32" of each other. Since new tires have a thread depth of 10/32" and your other three tires are at 8/32", you can just buy a new Bridgstone tire and put it on. Once your other tires fall below 6/32" and this happens again, then you can have tirerack shave the tire to match the other tires thread depth to within 4/32".

Tire Tech Information - Matching Tires on Four-Wheel Drive & All-Wheel Drive Vehicles

canon_mutant

Tirerack will shave a matching new tire down for you . . . or they did a couple years ago for me anyway.

motoguy128

+1 on same brand and model. Overall diameter can vary between tires. Plus handling characteristic and behavior can vary.

IF possible, I'd put the new tires on the driver side front. This tire has the most load most of the time, so the loaded diameter will be normally smaller... and it normally wears fastest.

superswiss

Actually, the common recommendation is to put new tires on the rear, because new tires on the rear axle help the driver more easily maintain control on wet roads. If the rear tires aquaplane, you gonna spin out, whereas if the front tires aquaplane you just keep going straight until they regain traction.

motoguy128

With quattro and traction control, I don't see that as an issue. Plus the rear wheels follow the front wheel tracks, so the front usually hydroplanes first, despite having more weight up front.

But you argument otherwise generally makes sense.

Besides if the front aquaplanes, you can't steer at all and could almost as easily lose control... or worse it veers right or left and you still slip out when the driver, predictably, over-corrects.

I'd still lean towards the front to balance wear faster and reduce wheel diameter differences and reduce rear differential wear.

superswiss

That's a bit of a false sense of security. Traction control is disabled above 40 km/h or something like that. So is EDL. The only thing potentially stabilizing the car at highway speeds is the ESP, which would attempt to selectively brake certain wheels to counteract the spin. However, that will only work if the required tires have traction. Similar for Quattro. Quattro is useless if the tires have lost contact with the road. Aquaplaning front wheels is easier to control for the same reason understeer is easier to control than oversteer. Neither one is perfect obviously and you can still end up in a ditch on the side of the road, however as long as the rear wheels have traction, the driver has a better chance to control the car, Quattro or not.

motoguy128

You not suite correct on several accounts. The AWD system has a permanent split and will distribute both acceleration and deacceleration forces. Its' driving both front and rear wheels all the time, it's a full time system. IF you lose front traction, you only option is to wait for the vehicle to slow down and regain it. You lose steering control and are at the mercy of inertia. esp will apply braking force to inside rear tire however to help out.

I know traction control keeps working above 40mph. I've seen it engage on snowy roads at 50mph on my E90 and wet and cold on-ramps at 70mph. I don't see why it would have a limit to the speed it operates at.

If the car over steers, the ESP can immediately apply rear opposite wheel and front inside wheel to counter the yaw motion. Further, a good drive always "tracks" any slide by keeping the steering wheels pointed in the direction they want to go. The car self corrects in most cases, especailly if you maintain some throttle. They tend to spin out when you panic and lift throttle or apply the brakes. I much prefer a car that's a little loose to too "tight" having driven both for many years.

But again, as mentioned, the rear wheels, unless the rear track is significantly wider, or staggered (this happens on some small economy and midsized cars) or had a severe forward weight distribution (again, FWD economy cars) the rear is less likely to hydroplane because it follows in the front wheel tracks.

Again, I can make a good argument most ways. But I agree, that on most cars, better tires in rear may be better for most drivers in many situations.

superswiss

All valid points, and I don't disagree with them. My main point is that little of that matters if the rubber has lost contact with the road, which is what happens when aquaplaning. The tires are literally floating on a cushion of water. If you are aquaplaning in a curve, then the rear wheels also don't track the front wheels. I guess it's debatable what's better in that situation. The front tires aquaplaning and the car careening into the other lanes or the rear tires aquaplaning and the car going into a spin.

This doesn't apply to the Q5, but on cars such as the (R)S4/5 the ESP if equipped so can leverage the rear sport differential to torque steer the car using the rear wheels, so that's another reason why one might want to make sure the rear tires have very little chance of aquaplaning. I actually did aquaplane once in the RS5 in a slight curve at about 65mph. The front was floating for about 2 seconds, but the car kept going through the turn aided by the sport differential. It was at that moment when I experienced how important the rear tires are.

Anyway, take the recommendation for what it is.