Wheel/tyre prob?

[angry]

I have a friend with a 1990 c4 with RUF 17" wheels the rears are 255/40/17 but the fronts are 8" wide rims running 235/45/17.
On smooth roads the car handles ok but on slightly/very rough roads it is absolutly shocking.I drove it today and nearly ended up on the wrong side.
It has bilstien shocks and springs....Is the front tyre size the problem??????
Thanks Dan

 

[Dave Wilkinson]

What is it that is shocking?? Tramlining or bump steering?? I think the 235 tyres are a little unusual (225s are more the "norm" or wider front wheels) but I'd be surprised if that were the problem. Wider fronts are always a good idea on a C4 to help the turn in (i.e. fight the understeer). Maybe it's more to do with the alignment rather than pure tyre sizes. If it were my car I'd be tempted to have the alignment checked before embarking on potentially expensive experiments.

Regards

Dave

 

[38F3E1]

Would be interested to know how low the suspension is set. The fact the car is fine on smooth roads but darty on rougher roads is the sort of behaviour you get with bad bump steer (caused by very low suspension). That and/or an over aggressive alignment setting could be the problem.

Ian.

 

[Hacki]

235 in the front for sure is a problem. But as always there are probably more reasons, e. g. camber and toe in and, as already mentioned, ride height. So the full set up has to be controlled and from my point of view the next fresh rubber should be 225/45 x 17 in the front.

Rgds,

Hacki

 

[Steve Brookes]

I can add to what others have said. I thought the 225s on the front of my C2 and or the lowered suspension were the cause of some quite alarming handling issues. The car would follow every bump and hollow in the road and literally jump sideways if I hit a bad depression that only affected one wheel.

A full alignment check found that the toe-in at the front was way out. The car now drives like a dream[]

 

[angry]

Cheers chaps,i had already told him of some of the above suggestions.Also he had non porsche rated Avon tyres on.
He is ordering a set of proper size/rated tyres and having the alignment done soon.
Thanks again.
Dan