Caster question
- Thread starter Okibonoe
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AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
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Could go either way depending on alignment factors.
If the rear stays at the same height, and the front was properly set to start with, then the caster will decrease.
But if the reduction results in significant weight transfer, it could go the other way.
If the rear is already sky high reducing the caster, and you jack-up the T-bars to maintain attitude then the lower control arm will reduce in effective length, and the uppers will increase. This increase the camber to positive and the upper arms I think will go forward, decreasing caster. But the Strutrods may also pull the LCAs forward for a net of no change.
My head hurts
Bottom line is this; when the LCA is dead level, it will put the camber curve in the best position to deal with suspension jounce and rebound. Adjust the rear ride height to whatever you like. Then deal with the caster, by moving the UBJ rearward as far as you can.
Then fix the bumpsteer you just created.
If the rear stays at the same height, and the front was properly set to start with, then the caster will decrease.
But if the reduction results in significant weight transfer, it could go the other way.
If the rear is already sky high reducing the caster, and you jack-up the T-bars to maintain attitude then the lower control arm will reduce in effective length, and the uppers will increase. This increase the camber to positive and the upper arms I think will go forward, decreasing caster. But the Strutrods may also pull the LCAs forward for a net of no change.
My head hurts
Bottom line is this; when the LCA is dead level, it will put the camber curve in the best position to deal with suspension jounce and rebound. Adjust the rear ride height to whatever you like. Then deal with the caster, by moving the UBJ rearward as far as you can.
Then fix the bumpsteer you just created.
Last edited:
AJ/FormS
68 Formua-S fastback clone 367/A833/GVod/3.55s
- Joined
- Jan 19, 2014
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- 24,940
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Depends on how you lower it, and where the UCAs were before the lowering.
But probably the caster would increase, If the UCA moves rearward carrying the UBJ with it then the caster will increase. The position of the UBJ, relative to the LBJ, determines the caster.
If the strut rod is parallel to the ground when you start, then any ride height change, will pull the LCA forward, increasing the caster. If at the same time, the UCA is moving rearward, then caster is increasing;
but if the UCA is moving forward, then the caster is decreasing.
To understand this you must realize that the UCA pivots are NOT parallel to the roadway, so the UCA is ALWAYS moving forward or backward and carrying the UBJ with it, relative to the chassis.
But if the strutrods are not parallel to the roadway, oh my head is hurting again, then the LCA could also move backwards and forwards, throwing a whole nuther level of complication into the mix.
The bottom line is this; if you just have to lower the car, do it either with tire sizes or drop-spindles, and set the suspension up to somewhere close to the factory settings.
If you need more caster, install the MOOG Problem-Solver UCA bushings, but be prepared to spend some time on the alignment rack.
But probably the caster would increase, If the UCA moves rearward carrying the UBJ with it then the caster will increase. The position of the UBJ, relative to the LBJ, determines the caster.
If the strut rod is parallel to the ground when you start, then any ride height change, will pull the LCA forward, increasing the caster. If at the same time, the UCA is moving rearward, then caster is increasing;
but if the UCA is moving forward, then the caster is decreasing.
To understand this you must realize that the UCA pivots are NOT parallel to the roadway, so the UCA is ALWAYS moving forward or backward and carrying the UBJ with it, relative to the chassis.
But if the strutrods are not parallel to the roadway, oh my head is hurting again, then the LCA could also move backwards and forwards, throwing a whole nuther level of complication into the mix.
The bottom line is this; if you just have to lower the car, do it either with tire sizes or drop-spindles, and set the suspension up to somewhere close to the factory settings.
If you need more caster, install the MOOG Problem-Solver UCA bushings, but be prepared to spend some time on the alignment rack.
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the reason you have caster change is the anti-dive top arms. they are angled so the torque reaction of braking lifts the front end counteracting the dive that would occur. car should brake level. That angle of the top arm moves the ball joint back as it goes up (suspension compresses) so it increases positive caster.
droop
bump
so yes ride height has a large effect on caster. lower arm shouldn't swing back and fourth that much as the strut rods pivot in the same plane as the inner bush on the arm.
Rake of the vehicle will have a smaller effect on caster but significant at extremes.
droop
bump
so yes ride height has a large effect on caster. lower arm shouldn't swing back and fourth that much as the strut rods pivot in the same plane as the inner bush on the arm.
Rake of the vehicle will have a smaller effect on caster but significant at extremes.
Boswell-
Very nice explanation. Great job.
Syleng1
Very nice explanation. Great job.
Syleng1
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