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Steering damper
My front tyres are 245/60-15 Avons and the steering geometry is perfect, car goes straight even with hands off the wheel. Toe in is about 0 if not 0.2º in.
When driving over bumps the steering wheel tends to snap left or right and I need to keep a steady hand on it while driving on bad roads. I was thinking in installing a damper for the suspension, before going through the steering box,like the offroad vehicles use. You know, one damper on each side going from each tie bar to the frame somewhere in the center. Has anyone experience with such a setup? Will it work without making the steering too heavy? |
Bump Steer
I don't know if a damper will help, but you are describing bump steer.
The ball joint needs to be as close to the middle of the tire as possible. If it isn't, when you hit a bump, it yanks that tire to the outside - assuming the ball joint center is to the inside of center. I had the same problem on my Pantera. The stock rims are 15x7 in the front. I switched to 15x8 with the extra 1" to the inside. It transformed the car. Naturally, I don't know your car or if you can change something to correct the offset. But that's where I'd look if it were my car. |
I would not think changing the tire width will do anything for bumpsteer. Bumpsteer is a relationship between the theoretical intersection point of the upper control arm, lower control arm, and tie rod end. When the intersection point of the tie rod is above or below the intersection point of the control arms, hitting a bump will either push the wheel toward toe-in or toe-out.
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Agreed.
The difference is the Pantera wheels. From the outside, they are identical - 15x7 vs. 15x8. You can't tell them apart - except that the 15x7 rims are usually stamped with their size. The extra 1" of the 15x8 Campy rims is on the inside of the rim - so it has a different offset. It still isn't perfect, but bump steer almost completely goes away with an extra 1". BTW, I have never heard of anyone installing a damper to stop bump steer. I've seen them on 4x4s before, but never sports cars. Of course, there are lots of things I haven't seen. |
Bump steer vs scrub radius
In my experience, jerking felt though the steering wheel was a scrub radius issue, which is the condition wkooiman described.
Bump steer, which is a change in toe as the suspension moves through its travel (caused by the condition joyridn described), gives more of a feeling of the car darting around without movement of the steering wheel. Rear wheel bump steer can be a real handful! |
As stated, changing the wheel width or offset of the wheel will not do anything for bumpsteer. That is a relationship to where the tie rod is placed versus the travel of the suspension. You can have a 10" wheel or a 4" width wheel and both will give you bumpsteer if the suspension is not set-up correctly.
I agree...wkooiman is describing scrub radius. |
Sorry - yes, I meant scrub radius. I have always incorrectly called that bump steer.
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Front suspension on my Contemporary is Jaguar XJ6, which is not known for bump steer generally.
But with wide tires in front 245/60-15 that is probably another matter. I have seen that bump steer kits are offered , which basically relocate the steering link bar higher or lower on the ball joint, so as to be as parallell to the lower A-arm as possible. I have not checked my setup, but will have a look. Maybe that is the problem. If not,since bump steer happens only on large bumps or potholes, I wiil have to install a damper somewhere. |
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