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2002 C4S - tire size & diff lock-up issues

Wheels and Tires

Vehicle Information: Model: 966 C4S; Year: 2002; Body Type: Coupe; Total Mileage: 34000;

Hi again Joel,Ive been reading all the posts on the subject of C4S all-wheel drive issues relating to larger tire sizes. I also know of a local guy who had a scary moment at the track, ostensibly due to this lock-up situation. What Im unclear about, is how do I determine what will pass muster (be within the 7% window) and what will cause me grief.My current setup is: stock turbo look wheels with Yoko AVS Sports 225/40 & 295/30 18s. These, of course, work just fine. The listed diameters are 25.2 & 25.0 respectively. What I what to upgrade to are Michelin Pilot Cups, 235/40 & 315/30 18s. The listed diameters are 25.4 & 25.5. The diameter relationship seems to be within 4% as does the general size relationships (2.0% &2.2% respectively). Of course, I may be comparing the wrong things (I have no idea if section width affects any of this.) So my question is will they fit, and will the diff not throw a fit?As always, thanks for your input.Paul

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