I just bought a 2006 C2S and it is current using Michelin super sport. The rear tires is out and the front still have 60% left. Can I replace the back with Bridgestone Potenza RE970 AS Pole Position and leave the front as Michelin Super sport ?

 

absolutely not recommended for a performance car.

if we were talking about an suv or some regular car in which you only drive at the speed limits i don't think its a huge deal; but on a 911 no way. to be honest on any rwd car i would recommended against mismatching tires.

 

Don't you like Michelin super sport ? Lot's of good review for it though..

 

Part of the answer becomes easier if the 60% tread tires are the same age as the worn out tires. Even with tread, the tire become harder over time and doesn't provide as much traction (either laterally or linearly) or flex.

I've occasionally replaced tired early on other cars just to get fresh rubber and improved grip on them (although my sport car tires haven't typically lived long enough to matter). I see you are in Texas also, so our tires get exposed to a lot of heat and makes this problem even worse.

Even if you decide the fronts are young enough to keep, they will still inevitably have experienced some age/heat related hardening and will result in a front/rear traction imbalance regardless of the manufacturer-induced differences.

 

As an aside: The new post that showed up reminded me, I've found the Bridgestones to have much less road noise than the Michelins that were on the car when I first test drove it. The dealer said that while part of that was due to age/wear on the Michelins, part of it was a difference in the tires themselves. Of course, maybe they were just trying to talk me into a less expensive tire since they replaced them as part of the purchase... but I don't think that was the case.