lowering car/ strut spindle height
11-15-2002, 11:08 AM
#1
Intermediate
Thread Starter
Join Date: Nov 2002
Location: Houston
Posts: 25
Likes: 0
Received 0 Likes
on
0 Posts
lowering car/ strut spindle height
How much does raising the strut spindle height help with eliminating bump steer on lowered cars? I know this is common practice on race cars. My car is a will be a "bitchy" stret car that gets driven to the track for d.e. and autox but not a full blooded race car.
12-06-2002, 05:58 PM
#2
AutoX
Join Date: Dec 2002
Location: United Kingdom
Posts: 11
Likes: 0
Received 0 Likes
on
0 Posts
I'm guessing you're talking about when lowering the car by raising the spindles instead of just adjusting the T-bars?
I believe the amount of bumpsteer produced is a direct result of the difference in height between the steering rack and the and the end of the tie-rod where it joins to the strut/spindle (plus probably a load of other complicated stuff i don't know about!).
If the spindle height is set so the tie-rod is parallel to the ground i.e standard ride height, then bumpsteer is minimal.
If the tie-rod is at an angle to the ground i.e lowered or raised ride height, then more bumpsteer is produced.
Therefore the amount of bumpsteer will increase as the difference in height increases, whether its by adjusting the spindle height on the strut tube (by modification) or adjusting the spindle height (in its O.E position on the strut-tube) by adjusting the T-bars.
To reduce bumpsteer on a lowered or raised ride-height car you need to get the tie rod more parallel with the ground.
This can be done by modifying the arm on the spindle by heating and bending, or by using a kit to space the tie-rod end away from the spindle arm.
Hope this helps, and any experts out there please let us know if i'm wrong. Nobody's perfect!
Regards, Jon.
I believe the amount of bumpsteer produced is a direct result of the difference in height between the steering rack and the and the end of the tie-rod where it joins to the strut/spindle (plus probably a load of other complicated stuff i don't know about!).
If the spindle height is set so the tie-rod is parallel to the ground i.e standard ride height, then bumpsteer is minimal.
If the tie-rod is at an angle to the ground i.e lowered or raised ride height, then more bumpsteer is produced.
Therefore the amount of bumpsteer will increase as the difference in height increases, whether its by adjusting the spindle height on the strut tube (by modification) or adjusting the spindle height (in its O.E position on the strut-tube) by adjusting the T-bars.
To reduce bumpsteer on a lowered or raised ride-height car you need to get the tie rod more parallel with the ground.
This can be done by modifying the arm on the spindle by heating and bending, or by using a kit to space the tie-rod end away from the spindle arm.
Hope this helps, and any experts out there please let us know if i'm wrong. Nobody's perfect!
Regards, Jon.
12-07-2002, 03:29 PM
#3
RL Technical Advisor
JMZ:
Good question that has a rather vague answer,....
Jon from the UK, is not quite correct about stating that bump steer is at its minimal with the tie rods parallel. There are many geometric factors at work here and the one big variable is each individual car's ride height. Final tie rod angles may not be parallel with corrected bump steer, depending upon that cars's ride height!
The thing to visualize here or better yet, measure, is the camber curve. The amount of camber change is not linear through the arc of the suspension, and matching the arc of the ball joint to the tie rod for bump steer correction is the Main Mission here. If a car is set low, optimal bump steer may not result in parallel tie rods; every case is different.
When a 911 with stock struts is not lowered much (1-1.5"), installing rack spacers may do the job quite nicely however, when the spindles are raised, the arc that the ball joint prescribes becomes very different from the arc of the tie rod and rack spacers simply are inadequate to do the job.
When we use raised-spindle struts, we always install the ERP Bump Steer kit so we can minimize this effect and set it precisely on each side. There is no other way to do this and in some cases, the steering arms are even re-arced to match.
The main reasons for raising spindles is the restoration of lost suspension travel and raising the front roll center back up where it belongs. Its critical to never let a 911 bottom out in a corner (front or rear) otherwise the spring rates leap to infinity and you start sliding, without warning.
Hope this helps,
Good question that has a rather vague answer,....
Jon from the UK, is not quite correct about stating that bump steer is at its minimal with the tie rods parallel. There are many geometric factors at work here and the one big variable is each individual car's ride height. Final tie rod angles may not be parallel with corrected bump steer, depending upon that cars's ride height!
The thing to visualize here or better yet, measure, is the camber curve. The amount of camber change is not linear through the arc of the suspension, and matching the arc of the ball joint to the tie rod for bump steer correction is the Main Mission here. If a car is set low, optimal bump steer may not result in parallel tie rods; every case is different.
When a 911 with stock struts is not lowered much (1-1.5"), installing rack spacers may do the job quite nicely however, when the spindles are raised, the arc that the ball joint prescribes becomes very different from the arc of the tie rod and rack spacers simply are inadequate to do the job.
When we use raised-spindle struts, we always install the ERP Bump Steer kit so we can minimize this effect and set it precisely on each side. There is no other way to do this and in some cases, the steering arms are even re-arced to match.
The main reasons for raising spindles is the restoration of lost suspension travel and raising the front roll center back up where it belongs. Its critical to never let a 911 bottom out in a corner (front or rear) otherwise the spring rates leap to infinity and you start sliding, without warning.
Hope this helps,
