Question on custom suspension
Question on custom suspension
(OP)
I'm building a new front suspension for an older kit car that had horrible geometry. This is a double a-arm front suspension, intended to be a road and track car. It is a difficult chassis to work with because the footwell intrudes on the suspension mount area, meaning that the chassis is not square (front to rear) at the A-arm mount points. (A-arms are canted forward, shorter in the rear than the front.) I've got modeled what I think is decent geometry, but I have a few questions that I'll probably ping the forum with in the upcoming days. First question-
I have roughly 4.5" travel, split evenly between bump and droop as designed. Under conditions approaching full bump, my instantaneous roll center dives below ground level. Is this acceptable, or will it produce unpredictable handling under full bump? Is it more important to simply maintain the height relationship between rear and front instantaneous roll centers, and to ignore actual roll center position at the extremes of travel?
Thanks!
I have roughly 4.5" travel, split evenly between bump and droop as designed. Under conditions approaching full bump, my instantaneous roll center dives below ground level. Is this acceptable, or will it produce unpredictable handling under full bump? Is it more important to simply maintain the height relationship between rear and front instantaneous roll centers, and to ignore actual roll center position at the extremes of travel?
Thanks!
RE: Question on custom suspension
I don't think your instant-center-below-ground is a disaster, a lot of OEM front suspensions do that (particularly MacPherson designs), but can you do any of the following and does any of it help:
- Raise the upper ball joint a bit (longer knuckle)
- Shorten the upper A-arm a bit (move chassis-side pivot a little outboard)
- Drop the chassis-side upper A-arm mount a bit (I'd rather raise the upper ball joint, but if you can't ...)
RE: Question on custom suspension
I've attached a few pictures of the rough design. I'm using wilwood pro spindles, (modified mustang II geometry,) chrysler large ball joints, and del-spheres on the inboard end of the arms. Because the upper A arm has to be so much shorter due to the chassis, it is very difficult for me to do anything to the roll center and maintain a reasonable camber curve.
RE: Question on custom suspension
Since roll center heights and available rebound travel shouldn't matter a whole lot when nobody is in the car driving it, it seems that all you'd need do would be to raise the empty static ride height up by enough to achieve your equal bump/rebound target when you (they) get in.
Norm
RE: Question on custom suspension
RE: Question on custom suspension
Cheers,
dynatune, www.dynatune-xl.com