Bump steer yet again.
Posted: Tue Jul 08, 2014 8:30 pm
I've been setting up the bump steer on my Plus Two while the body is off the chassis.
I'm using a laser beam aligned with the stub axle centre. The beam points forwards (ie perpendicular to the stub axle axis) onto a target about six feet away. The chassis height is fixed and the springs and shock absorbers have been removed. I'm moving the suspension arms through their full range of movement.
Ideally the beam should produce a straight vertical line on the target indicating no bump steer as the suspension moves. The best I can achieve is a curve, a tangent to which is vertical. This curve is symmetrical about a horizontal line drawn through the ride height position. ie toe in increases by equal amounts on both compression and droop.
Should I be able to do better than this?
I realise that my measurement method is flawed because the track changes as the suspension moves up and down. Tomorrow I plan to reflect the laser beam off a mirror onto a target mounted below the laser beam. As the beam and target will move together, this will cancel out the change in track. However this will produce a horizontal line on the target rather than a curve. I'll have to measure deflection at various points and plot a curve from that.
I'm having to use a lot more shims than Lotus ever did, but reading through previous posts this seems to be quite common.
Cheers, Graham.
I'm using a laser beam aligned with the stub axle centre. The beam points forwards (ie perpendicular to the stub axle axis) onto a target about six feet away. The chassis height is fixed and the springs and shock absorbers have been removed. I'm moving the suspension arms through their full range of movement.
Ideally the beam should produce a straight vertical line on the target indicating no bump steer as the suspension moves. The best I can achieve is a curve, a tangent to which is vertical. This curve is symmetrical about a horizontal line drawn through the ride height position. ie toe in increases by equal amounts on both compression and droop.
Should I be able to do better than this?
I realise that my measurement method is flawed because the track changes as the suspension moves up and down. Tomorrow I plan to reflect the laser beam off a mirror onto a target mounted below the laser beam. As the beam and target will move together, this will cancel out the change in track. However this will produce a horizontal line on the target rather than a curve. I'll have to measure deflection at various points and plot a curve from that.
I'm having to use a lot more shims than Lotus ever did, but reading through previous posts this seems to be quite common.
Cheers, Graham.