18" Tyre size?

[Guest]

Hi, I have a C2S on 17" wheels (255/40/17 on the rears). I have just got my self a set of 18" Turbo II wheels (11x18 rather than the Tubo I's 10x18). now should I go for 285/30/18 tyres as be suggested in the manual (-8mm differance in overall diameter compared to the 17's) or 295/30/18 as per the 996 C4s/Turbo (-2mm differance compared to 17's). So the 295 give a closer roling diameter to the orignial 17's but the maunal recommend 285's. So any recommendation on which rears to get? Mainly dry, fast road use. Will 295's give more understeer?
Cheers

 

[m bannon]

Hi Mankster,
I run 285 on the rear, same wheels and as yours is an 's' the clearance should be the same.
I'm not sure where the 295 as per c4 / turbo info came from. , my turbo specifies 285.
With regard to oversteer / understeer, I have found that this is much more to do with tyre pressure than actual tyre width.

I'd go for the 285.
mark

 

[Guest]

Thanks Mark and Maurice, The 996 Turbo and C4S definately had 295/30/18's onthe rears. I figured it was because the Turbo II rear wheel was 11" wide rather than 10" like the Turbo I wheel on the 993 Turbo (which had 285/30/18). I was just worried that 285 might not be wide enough to sit properly on the 11" wide wheel.

The rear wheels are ET45 as per the 996 Turbo, if they dont stick out as much I could always add 5mm shimms/spacers to take it out to ET40.