ChicagoGSf

Does anyone know how detrimental replacing only two out of four tires on an AWD car can be? Here’s my situation: I had a set of Pirelli P7 tires on my GS350, which had about 20,000 miles on them and were two years old; they were also under warranty. Yesterday, I discovered a nail in the sidewall of one tire. Since the P7 is no longer available, I opted to replace two of the tires with Pirelli Zeros and decided to rotate them, putting the new set in the back.

I’ve recently read that replacing only two tires can be harmful to the AWD system. Should I be concerned or should I replace the other two tires as well? Unfortunately the warranty only covers the damaged tire…. I should have put nails in the other 3🤬

bclexus

The Pirelli P7 AS tire is still available - it's been redesigned and improved, and now is called the P7 AS Plus 3.

Since you already purchased the Pirelli Zero tires - as long as the the Pirelli Zeros you opted to purchase are rated 'all-season' tires and not P Zero 'Summer performance' tires you should be okay putting them on the front or rear.

I would most definitely not mix summer performance tires with all-season tires - nor would I ever put summer performance tires on any vehicle - including an AWD vehicle - that may be driven in sub-45 degree climate conditions.

Summer performance tires become rock-hard and brittle, and the rubber cracks open in sub-45 degree temperatures. AWD becomes no-wheel drive with the tires unable to get traction like they are made like hockey pucks. The slightest turning force or change in acceleration/braking can bring about a spinout like the tires are made with ball-bearings for tread.

Lanson

If I read you correctly, you are curious if the tire final circumference difference front and rear will cause "binding" or other issues, right? Looking back, I realize that I've owned quite a few AWD vehicles. I know for my AWD MDX, AWD Ford Flex, and my AWD Subaru WRX, all those vehicles have/had different AWD drivetrain mechanisms so they have different requirements on tire "tolerance". Manual transmission Subarus are the tightest (lowest) in tolerance, basically if you need to replace one or two, you replace all unless it's like 1-2/32nds difference and that's become the industry standard for "full-time AWD systems" - blanket statement - but I think that's a slight cop-out against pump and clutch systems. The GS system, with a 70/30 split in normal mode and 50/50 mode for snow, clearly is advanced and probably pretty flexible. But I do think that if I lost a tire or two, I personally would go ahead and replace all 4 on my AWD GS, and consider mounting one as a fullsize spare (for long highway trips), and sell the rest on Craigslist for some bucks. I do think I would be ok with completing a road trip on a newer (or older) tire, but not thousands of miles if that makes sense.

So what do you do? I think it comes down to what you risk. I'd probably give this system the same tolerance as the WRX, plus maybe an extra 32nd or so.

Long term, definitely match them up for optimal comfort and performance.