What is bump steer? How to conquer bump steer in drag racing.

Bump steer explained

A lot of people don’t understand bump steer, or really address bump steer in their drag car build, but it is actually pretty important. Bump steer is when the car is on the starting line and it’s at ride height then when you let go of the button or the clutch and you dump it the front end comes up and your wheels toe in or out as the strut extends.

Why does it matter?

Here’s an example of of bump steer

Say the car took off and your front end lifts of the ground your strut extends and as it extends it rotates and your wheels toe in.  When your wheels land back on the track they have to straighten back out.  This straightening back out process is going to scrub off a lot of elapsed time and of course that’s no good. We want to be as smooth as we can from point A to point B.

Correcting your bump steer

You have a few components to deal with to get your bump steer correct.  Your tie rod, lower control arm (which is your camber bar), and your forward control arm (which is your caster bar). Your lower control arm (camber) bar is going to be the most important bar for your bump steer.

You will want your tie rod parallel to your lower control arm.  The way we do it is to take a digital level and find the angle of the lower control arm and then get the angle of the tie rod.  Then you can shim the tie rod down to match the lower control arms angle.  We don’t recommend shimming the tie rod higher than the steering arm since that is not a correct installation.  You may have to mount your lower control arm differently to match the tie rod if that is the case.

Matching the angle of the tie rod to the lower control arm is key to keeping bump steer correct and your drag car moving properly.

Conclusion

All struts rotate as they extend and each manufacturer can provide data showing the expected rotation.  Incorrect bump steer costs you valuable elapsed time and, as you know, in drag racing fractions of seconds count can mean the difference in winning or losing.  To get the fastest time down the track you need to keep it in check and make sure that it is not affecting your car.  It can be an easily fixed by just shimming your tie rod lower to match the lower control arm.  If you need to raise your tie rod it may be a more difficult correction since it may result in the replacement of your steering rack.

You can check out our bump steer video where Andy explains bump steer on one of his cars.