I have a 986 boxster with OEM Cayman wheels (see sig)... It's now time for new tires... currently they have 225/40/18 in front and 265/35/18 in back... but when i check online, the '06 cayman with 18's shows to use 265/40/18 for rear, a different size...

Was this probably to correct the speedo and get closest in circumference to stock? Should I stay with 265/35 or should I go back to 265/40?

 

I would keep the stock 18" 986 size but go here.
http://www.1010tires.com/tiresizecalculator.asp

 

i went to 19's on mine. the rears required spacers and extended lug bolts in order to do so though.

best wishes!

 

Ah, thanks.. I didn't even think to check... the 18" boxster S wheels are 265/35 and the 18" cayman S wheels use 265/40

265/35 it is

Now to pick out some tires