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Used Porsche Cars for sale in Slough, Berkshire | RSJ Sports Cars

17" wheel/tires 90 C4

E

eweyls

New member
Joined
27 May 2008
Messages
5
Hello, I recently fitted 17" Cup wheels to my 1990 C4 with negative results. Terrible shake and vibration, is the computer sensing slippage and engaging traction control? The manual states this could happen if the sensors detect a different tire diameter. The standard wheel is 205 50 16, 225 50 16, fitted were 235 40 17, 275 40 17 ( from my Cup car ).

The switch back to the 16" cured the problem. The primary reason is apperance and I am not attempting to gain and performance gains.

Thanks for any help
Erik
 
Your tyre dimensions are certainly a bit different to those normally used with 17 inch wheels i.e. 205/50 17 on the front and 255/40 17 on the back are the standard recommendations.

Plenty of people try slightly wider tyres on the front to help reduce understeer, but the biggest I've heard used on the front is 225/45 17 which makes me wonder if your extra width and lower profile on the front is indeed causing issues with the 4WD system :?:
 
cup

what a coincidence ,only last night my passenger told me there was a small round light coming on intermittantly next to my 4 wheel drive switch.
we were going fast over a bumpy road to work.
i have never noticed this before ( but never looked to be honest)
the manual says it works when the wheel speeds are not the same.
i recently fitted 17" cup wheels with 225/45 on the front and 255/40 on the rear.
am i right to assume it probably did this with the standard 90 wheels on but i never noticed ?
and all is well
thanks steve
 
Gentlemen, thanks for your help. The problem, confirmed by you and Porsche, is the 40 profile with the front tire.
Erik
 
Re: cup

stevebozzy said:
what a coincidence ,only last night my passenger told me there was a small round light coming on intermittantly next to my 4 wheel drive switch.
we were going fast over a bumpy road to work.
i have never noticed this before ( but never looked to be honest)
the manual says it works when the wheel speeds are not the same.
i recently fitted 17" cup wheels with 225/45 on the front and 255/40 on the rear.
am i right to assume it probably did this with the standard 90 wheels on but i never noticed ?
and all is well
thanks steve
Click to expand...

Steve,

What you are seeing is perfectly normal when driving over bumpy roads. The PDAS will momentarily engage when traction is lost over the bumps. I have to admit that the light isn't in the best of places to catch your eye - particularly when the going gets rough!!

Regards

Dave
 
I fitted the bulb into the main cluster, which flashes green when the PDAS system senses a difference. I know Porsche opted not to fit this at the 11th hour as they thought it would be distracting, but I just wanted to see what it did.

Cheers,

Neil
 
Steve, thanks for the welcome!!!

Cheers,

Neil
 
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