What is Bump Steer?
Is your car going haywire each time you hit a pocket in the road? We’ve got the info you need on bump steer and how to fix it.
Written by Natalie Todoroff
Reviewed by Melanie Reiff
Bump steer results from a misaligned steering rack. It causes the steering wheel to turn by itself and the tires to “toe in” or “toe out” when you drive over a bump. Although it’s dangerous for everyday drivers, bump steer can be absolutely fatal if you’re out on a racetrack.
If you own a car, chances are, you’ll experience bump steering at some point during your vehicle ownership. No car is immune to it: everything from a beat-up minivan to the most finely-tuned mustang or drag racing car can experience bouts of bump steer from time to time.
Consider this article bump steer explained.
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What is bump steer?
Bump steer describes the phenomenon of your car turning itself when you go over a bump, pothole, or other hiccup in the road. When your front wheels move up and down, bump steer causes your steering wheel to turn on its own.
Not only does this create dangerous driving conditions, but driving with bump steer can also wear down your tires and decrease your vehicle’s handling.
Picture yourself driving. You hit a bump with your front right tire. Bump steer is when the suspension on the right side compresses, causing the tire to toe-out, which makes the steering wheel turn to the right without you directing it to do so.
How bump steer works
To fully understand what bump steer is and what causes it, we’ll first have to do a little steering geometry. A rack and pinion steering system is composed of many different parts, two of them being the control arms and tie rods.
The upper and lower control arms join the wheels to the chassis, which makes the wheels move up and down. The tie rods, on the other hand, connect the wheels to the steering rack and allow them to move from side to side.
Stand at the front of your vehicle, and envision three imaginary lines shooting out of the upper control arm, lower control arm, and tie rod.
The point where the imaginary lines form the upper and lower control arm meet is called the instant center. If the angle of the tie rod does not pass through the instant center, you will experience bump steer.
Bump steer is not only created by misalignment, though. Your tie rod length must be a specific distance as well. If your tie rod is too short, the front end wheels would toe in when your wheels deviate from their standard ride height position. If your tie rod is too long, the opposite will happen.
MORE: How often to check your car’s tire pressure
How to measure bump steer
If you’re experiencing bump steer, you’ll more than likely be able to feel it while driving. Not only that, but your tires may wear out faster than they normally would, and your car won’t handle as well as it used to around tight turns.
While it may feel bad, there’s actually a way to tell just how bad your bump steer situation is with a little help from a bump steer gauge! Here’s how to do it:
Step one: Prepare your car for bump steer measurement. Set your car at ride height, and make sure that your caster, camber, and tie rod are set.
Your steering rod should also be centered so that the tie rod is positioned over the inner pivot points and lower ball joints.
Step two: Put your car up on jack stands and remove the wheels. Center and lock your steering wheel.
Step three: With a tape measure, measure the distance between the lower ball joint and the ground. Jot it down on a piece of paper or on the notes app in your smartphone for future use.
Step four: Take out the sway bar and springs.
Step five: With the measurement you took note of earlier, bring your vehicle’s front suspension back up to its proper height.
Step six: Secure the bump steer gauge to the hub with a bolt.
Step seven: Jack your vehicle up an additional two or three inches of both compression and rebound and note your results.
Step eight: Grab a bump steer kit or shim as needed. For context, a bump steer kit typically includes end links, taper shafts, washers, bushing spacers, and more.
MORE:
How to correct bump steer
Now that you’ve got your bump steer measured, it’s time to move on to the next step: correcting your bump steer.
The table below has some tips on how to go about your bump steer correction for vehicles with front suspension.
Symptom | Solution |
|---|---|
Toe in on compression and toe out all in one direction | Low inner tie rod or lessen shim on outer tie rod |
Toe out on compression and toe in all in one direction | Raise inner tie rod or increase shim on outer tie rod |
Toe in both compression and rebound | Increase length of tie rod |
Toe out on compression and rebound | Decrease length tie rod |
Toe out on compression, in on rebound, and back out with more rebound | Decrease shim on outer tie rod and decrease length of tie rod |
Toe in on compression, out on compression, and back in with more rebound | Increase shim on outer tie rod and increase length of tie rod |
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MORE: How to check and add power steering fluid
Difference between bump steer and roll steer
After reading this, you may think to yourself “bumper steer sure sounds a lot like roll steer.” And you’re not all that far off! However, bumper steer and roll steer measure different things.
Bump steer is, technically speaking, a measurement of how much toe angle change occurs with suspension vertical travel (aka, when your car hits a bump).
Roll steer is calculated in a similar way—it’s a measure of the angle change that occurs when a roll angle is applied to the body of the vehicle.
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What causes bump steer?
Generally speaking, bump steer is caused when certain parts of your steering system (the upper and lower control arms and tie rods) are out of alignment or improperly fitted to the chassis.
Most often, it’s due to changes in ride height from damaged rack mount bushings, loose mounting bolts, or loose upper strut mounts.
What is the effect of bump steer?
When you drive over a bump and your vehicle automatically pulls to the left or right without you moving the steering wheel, your vehicle is experiencing bump steer.
How do I get rid of bump steer?
To eliminate bump steer, you will need to adjust the length of the tie rods and shim as needed. It’s helpful to get a bump steer gauge to help determine how severe your bump steer issue is and how much you need to adjust your tie rod ends.
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