1998 996 rear tyre size ???

[22/11/71]

I've just bought a 1998 996 with 18" turbo wheels and it has 265 35 tyres on the rear.

Should they be 285 30 ????

[oldtimer]

Yup, 265 x 35 is what the handbook says. I've got these on 'turbo-look' aftermarket wheels on my 98 C2, and it does 'look'undertyred, but works very well. Done some track days in it which is basis for my opinion.
Rule of thumb is that tyre width should roughly equal wheel depth , eg 255 or 265 would both be OK on 10inch (10J) wheels. You get better profile ( flatter tread X section) than if you put fat tyres on skinny rims.

285 will probably fit standard 996 C2, theres room, would look sexy and cost more, but you dont have enough power @300 bhp (98 car) to make an improvement in performance (IMHO)