Managing Bump Steer And Why You Need To Know About It

Ask almost any gearhead, and they’ll tell you that a lowered vehicle will always look cooler than the way it came from the factory. Automobile manufacturers know this, too. In fact, it’s a little known secret that car manufacturers used to load a car with weights or bricks to compress the suspension during new-model car shows. This lowered the car a little so it would look more enticing to potential buyers. But, given all the associated issues with a lowered vehicle, manufacturers decided to play it safe and designed a little more suspension travel into regular production cars.

A big advantage of lowering a vehicle – aside from looks – is that it lowers the center of gravity for better handling and control. While manufacturers used weights to bring the vehicle down, properly lowering a car requires a bit more work and the right components. Lowering vehicles goes back to the 1950s. It is a very common modification today, and the performance industry is growing by leaps and bounds in this area.

But, when you lower a car without modifying other important components, it can affect handling and steering. This will be more noticeable during cornering and when encountering uneven pavement, especially at speed. To help explain that a little more, we reached out to Chris Alston’s Chassisworks to learn about its bump steer kits, and why they’re sometimes needed. These kits will help correct steering issues that come about from lowering a car – an often overlooked aspect.

What Is Bump Steer?

In layman’s terms, bump steer is just as it sounds: when you hit a bump, it changes the car’s steering angles. Bumps cause the suspension to compress, and that compression causes the tie rods to articulate as well. This articulation changes the steering angle of the front wheels. The video above is a crude example of how this occurs, but it’s a simple one that shows how all components move at different angles and rates of travel.

Most everyone knows that a standard alignment for the street requires a slight toe-in. This means the leading edge of the tires point inward (usually 1/16-inch or so). Depending on whether you have a front or rear-steer linkage, toe-in and toe-out are affected when you go over bumps or uneven pavement. If your car has a front-steer system, it goes toe-out. A rear-steer system will push, and cause the wheels to toe-in. It also depends on where the tie rod is connected, and the angle of the tie rod. If it’s angle up when static, it won’t push, it will pull. If it’s angled down when static, it pushes. That’s the simple explanation of bumpsteer and how it affects the handling of your vehicle.

In technical terms, however, bump steer can get pretty intense. When a vehicle is designed, the length and angles of the control arms – and the angle of the tie rods – are all part of the design to alleviate as much bump steer as possible. Engineers calculate the angle each control arm rotates during suspension articulation and they find the instant center, which is the point where an imaginary line from the ball joint pivots and the control arm pivots meet, as shown in the image above.

As you can see, the instant center changes as the suspension articulates. The tie rods typically have an angle that is between the upper and lower control arm angles, and that angle lines up with the instant center. Each time the arms and tie rods move, they move at different rates and angles, thus changing the instant center.

Alignment issues will arise when you hit bumps. This can’t be avoided. Lowering a vehicle can exaggerate these issues, but a bump steer kit will correct the improper angles and reduce further bump steer. Simply getting a new alignment without addressing bump steer won’t allow optimum performance.

Bump Steer Kits are more than just a couple of spacers to move the tie-rod end. The kit allows several adjustments to both the spacing and the length of the outer tie rod.

Think about the last time you drove on an uneven road and how the car wanted to pull to one side or the other. This is how bump steer can affect the handling.  That’s why it’s mandatory to – at the very least – get a front-end alignment when you’ve modified your suspension in any way. Suspensions are all about geometry – the subject many of us hated in school.

The discussion can get very complicated, so instead of confusing you with a lot of technical diagrams, angles, and mathematics, we’re going to discuss how lowering a vehicle affects bump steer. Lino Chestang, from Chris Alston’s Chassisworks, will give us some more insight on what bump steer is, and how to correct it.

gStreet billet-aluminum uprights are available from Chris Alston’s Chassisworks, and are built to utilize their bump steer kits.

Bump Steer Kits For Lowered Vehicles

“At a minimum, all lowered cars should have the alignment set when at the lowered ride height. But, consideration for a bump steer kit should increase as the ride height gets further from stock,” Lino stated. Because of the change in control arm angles and the instant center, the tie-rod angle needs to be modified as well. Since the steering rack (or the idler and pitman arms) are fixed to the chassis, after lowering, the tie-rod angles are changed and that will affect the steering.

If you’re not sure you need a bump steer kit, Lino had this to say, “If the car is feeling “darty” or unstable during firm braking or when encountering dips or bumps in the road, it’s a sign of a possible bump steer issue.” He also advises to make sure the alignment is within spec and that all tie rods and ball joints are functioning properly before purchasing a bump steer kit.

Tie-rod length is also a vital adjustment when installing a bump steer kit. It's recommended that a professional alignment shop handle the installation, it does require experience.

“The negative effects of bump steer or poor alignment are more noticeable with lower profile or stiffer sidewall tires, which is why bump steer is more of a concern on Pro Touring or road race cars,” he stated. He also affirmed that not correcting bump steer could result in either inside or outside wear on the tires. However, poor handling would be the sure sign that something isn’t right with the car.

For those who road race or autocross, bump steer can really affect how the car handles, and make it more difficult to control. “Driving a car near its performance limits without minimizing bump steer can leave a bit of unpredictability in the handling. Adding a bump steer kit and tuning the steering can give the driver a lot more confidence,” he added.

What Does A Bump Steer Kit Change?

A bump steer kit changes the angle of the tie rods so they align with the instant center. As the car lowers, so does the steering rack. The tie rods do not, which means the outer tie-rod angle changes, taking it out of instant center. That, in itself, will affect the alignment so much that you’ll almost instantly wear out your tires – if you can drive the car at all. Sometimes, a suspension drop will create such an alignment issue that the vehicle won’t even roll. In that case, it’s recommended to trailer it to the alignment shop.

By changing the location where the tie rod meets the steering knuckle, the tie-rod angle can be adjusted and aligned closer to instant center — which is what a bump steer kit does. But they aren’t a one-size-fits-all component. When they’re installed, everything needs to be checked, preferably with a bump steer gauge. This is not for the novice, and if it’s not adjusted properly, your bump steer kit can leave you even worse off than when you started.

By moving the mounting point of the tie-rod end (blue line) and adjusting the length, bump steer can be minimized. Although it can't be eliminated, Bump Steer Kits will help you regain control when you're pushing your car to its limits.

In the images above, you can see how the Instant Center changes as the suspension moves. With the steering linkage fixed to the chassis, lowering the car changes the angles of the tie rod, and it creates excessive toe-in or toe-out. A bump steer kit will help align the tie rod to instant center, and minimize bump steer.

Before you purchase a kit and think it will solve all your bump steer issues with a simple installation, there’s much more to it. There is a process to installing a kit, much like there is for an alignment, and adjustments that need to be made, including the tie-rod length. With each kit, a set of installation instructions is included, and all parameters must be measured or you could run into tire wear or poor handling issues.

General Adjustment Rules:

  • If compression travel toes-out and extension travel toes-in, then the outer tie-rod is too high.
  • If compression travel toes-in and extension travel toes-out, then the outer tie-rod is too low.
  • If compression travel toes-out and extension travel toes-out, then the tie-rod assembly is too short.
  • If compression travel toes-in and extension travel toes-in, then the tie-rod assembly is too long.

When your car or truck was designed, suspension travel, steering angles, and control arm angles were factored in. Bump steer is one reason why an alignment must be done with the suspension loaded. Eliminating bump steer altogether can’t be done unless you drive a forklift, or you don’t want suspension travel. But with the right setup, you can control any significant amount of bump steer, and Chris Alston’s Chassisworks manufactures kits to provide more confidence out on the road – and track. If you have any questions about kits and applications, be sure to give them a call. They’ll steer you in the right direction.

Article Sources

About the author

Michael Harding

Michael is a Power Automedia contributor and automotive enthusiast who doesn’t discriminate. Although Mopar is in his blood, he loves any car that looks great and drives even faster.
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