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Bump Steer — parasitic steering (literally: impact steering), a characteristic of the suspension system when hitting a bump causes the wheel to turn involuntarily without driver input.

To get an immediate understanding of what's being discussed, watch this video:


But why is it dangerous and scary?

Loss of stability at high speeds upon hitting a pothole.

Why does it happen?

Every suspension system has an instantaneous pivot point. If the steering linkage isn't aimed at this instantaneous center, then wheel turning will occur as the suspension moves because the steering linkage and the suspension move around different centers. Even if the steering linkage is correctly positioned, its incorrect length would prevent it from continuing to aim at the instantaneous center when the suspension moves. Therefore, both the position of the steering linkage and its length are equally important.

To achieve zero 'bump steer', the ends of the steering linkage must be on an imaginary line passing through the outer upper and lower control arm joints, as well as another imaginary line passing through the inner upper and lower control arm joints. Additionally, the longitudinal axis of the steering linkage should intersect with the instantaneous center obtained by extending the lines of the upper and lower suspension control arms (see diagram below).

The instantaneous center is an imaginary point that is found by drawing a line through the outer and inner joints of the upper control arm and its intersection with another line drawn through the outer and inner joints of the lower control arm. The intersection of these two lines is the instantaneous center.

If you still don't understand anything - it's okay.There's an excellent online program for suspension calculation, with beautiful visualization.The main thing is to choose your type of suspension and then enter your size measurements (measure with a tape measure).

I did the same.

This link will help you understand how your suspension works after lowering using your car as an example.

It turns out that either find a rack 54 cm long (exactly such distance between lower control arm mounts) or something close in length and move the rack up/down. And this second option doesn't work at all, there's no room.

To illustrate, I'll show some great photos

He encountered a similar problem. The rack from a 90 model fits almost perfectly but it is too long.

There is a solution; starting in the '80s they started implementing racks. You can find them but you have to search.