twitchy steering

[breezeblock]

put a bit more camber on the front wheels and the steering has went twitchy at speed adjusted tracking and its not really any better any suggestions camber has went from 0.75 deg to 2

[Mackmot]

bump steer, read about it.

[Chris Y]

You're also reducing the contact patch on the front wheels - this will make the car more twitchy, as there's less resistance to little bumps in the road that want to push the car sideways.

[Al Weyman]

Do you have enough caster dialled in, the more the better the straight line stability and camber gain in cornering, maybe you set up alterered the caster when adjusting the camber, you have to be careful about that on my early Camaro.

[breezeblock]

Originally Posted by Mackmot

bump steer, read about it.

definanately not bump steer will try a bit more caster though

[greenamex2]

The rule of thumb is around two degrees of caster for every degree of camber.

On a very front light car (eg mid engined or Caterfield) then double that to four degrees of caster for every degree of camber but then you shouldn't have much camber because, hopefully, the suspension has been designed properly.

[graham bahr]

ok you reset the tracking, but with such a big camber change you might need to reduce the toe setting a bit

[johnny yuma]

Not many cars are designed with 2 deg static neg camber,so you are too far off standard geometry for sensitive straight line feel,the desired alignment between inner lower control arm bushes and the inner tie rod ball joints[ as a straight line],which stops bump steer,may be not quite right.If you run toe out like many racers this won't help either. The Ackerman angle requires a straight line between centre of rear axle,outer rod end balljoint and lower steering pivot point.Hard to measure at home but easy to stuff up.Go too far from standard and the car doesn"t know which front wheel to follow.Better to run less camber,more caster and a smidgin of toe in.

[Al Weyman]

Well I was hitting some high mph at Brands GP in my IROC on Saturday and I have just wound 3 degrees camber on the front and it was as straight as an arrow and it was not chewing up my tyres or understeering either. As a matter of interest what car is it?

[graham bahr]

i was nudging 140mph with 2.5 degrees neg camber, 9 degrees castor 2mm toe in and i had excellent straight line stability, no cornering problems and no tyre wear issues

[johnny yuma]

Originally Posted by graham bahr

i was nudging 140mph with 2.5 degrees neg camber, 9 degrees castor 2mm toe in and i had excellent straight line stability, no cornering problems and no tyre wear issues

You and Al obviously have very well set up cars--Al last year didn't you have some tyre chewing issues? Interesting to see Graham you run a little toe in, not everyone does ,it seems right to me.Were your caster/camber settings attained without post-factory mods?

[graham bahr]

i have a set of blank universal top mounts, i get the strut where i want it, then drill through the top mount holes in the bodysheel into the top mount and then tap a thread in the hole.

a little toe in is or was generally always the way to go on a rwd car, its nice and stable and the tyre temps say its good too.

i always toe fwd cars out a bit, it helps traction and turn in, although too much particlary on a lower powered car will cost straight line speed

[Al Weyman]

Yes it was wearing the front tyre very quickly which is why I increased it on this car, I just simply redrilled the fletch panels. On the yellow car that was also chewing tyres but I have done a number on that, the caster was miles out and I was actually getting negetive camber gain in cornering, its much better now and again as straight as an arrow with nearly 3 degrees on the front.

[johnny yuma]

Originally Posted by Al Weyman

Yes it was wearing the front tyre very quickly which is why I increased it on this car, I just simply redrilled the fletch panels. On the yellow car that was also chewing tyres but I have done a number on that, the caster was miles out and I was actually getting negetive camber gain in cornering, its much better now and again as straight as an arrow with nearly 3 degrees on the front.

Thanks for your replies Al and Graham--Al did you mean you WERE getting POSITIVE camber gain ?? Neg gain is whats desirable ,I thought , in corners.

[breezeblock]

put some more front caster on it . the top wishbones were adjusted to the max so i had to turn a bit off the adjusters has made a heck of a difference a lot more stable but it made the oversteer worse so had to put more camber on the back to counteract this with much success

[Al Weyman]

Originally Posted by johnny yuma

Thanks for your replies Al and Graham--Al did you mean you WERE getting POSITIVE camber gain ?? Neg gain is whats desirable ,I thought , in corners.

Yes thats correct, I had 0 degrees castor on one side and about 2 degrees the wrong way the other side, not good! Now I have it set at about 3 or 4 degrees both sides I get about 1.5 degrees camber change in the right direction (i.e. negative).

[johnny yuma]

Al have a look back thru a message I sent you last year for photos of type of early fifties Australian Holden Peter Brock is bringing to Goodwood Revival to take on the mighty Morris Minor,Austin A30,Riley and Jaguar. You heard it first from J.Yuma.

[greenamex2]

Originally Posted by Al Weyman

Yes thats correct, I had 0 degrees castor on one side and about 2 degrees the wrong way the other side, not good! Now I have it set at about 3 or 4 degrees both sides I get about 1.5 degrees camber change in the right direction (i.e. negative).

Funnily enough that matches the '2 degrees of castor for 1 degree of camber' rule of thumb!