I have an '08 Cayman base with the 17" factory wheels. I've just acquired a set of 18" oem Turbo Twist wheels, as pictured, at a very good price but would appreciate some expert advice.

The new (to me) wheels were described as 18x8 52 ET front and 18x10 65 ET rear. I'm planning to mount 235/18 tires in front and 265/18 tires in the rear. I'm also planning to re-use the TPMS from my existing wheels.

Question #1: Are my proposed tire sizes appropriate (conservative street and freeway driving) or should I go wider, like 275 in the rear?

Question #2: Assuming I go with my proposed tire sizes, will I need spacers in the rear, and if so, what thickness and where to buy? I'd like the tires to fill the wheel wells but not extend beyond them.

Thanks for looking!

 

Cayman S offsets with 18" wheels are 57 F and 43 R. The center-line of your new rear wheels will be inboard compared to Cayman wheels. You will need about 20 mm spacers on the rear. The 10" wheel can definitely handle a wider tire but no use other then appearance. A wider rear tire relative to the front will increase under-steer.

 

Thank you, that's what I needed to know. I don't think I see any purpose in going wider than 265 in the rear either, especially if it would lead to increased understeer.