One critical factor that can significantly affect a car's performance is bump steer. Bump steer is the unintended change in toe angle that occurs as a vehicle's suspension travels through its range of motion. In this blog post, we will explore the concept of bump steer, its negative effects on vehicles, and how a few products can help eliminate or minimize bump steer.
Understanding Bump Steer
Bump steer occurs when the wheels of a race car change their toe angle (the angle of the wheels in relation to the vehicle's centreline) as the suspension moves up or down due to bumps in the road. This phenomenon can lead to unpredictable and undesirable handling characteristics, making it challenging for inexperienced drivers to maintain control of the vehicle and making it unpredictable for experienced drivers.
Negative Effects of Bump Steer
Reduced Stability: Bump steer can cause the car to become unstable when encountering bumps or uneven surfaces on the racetrack. This instability can result in erratic handling, making it difficult to maintain a consistent racing line or a smooth and stable drift without corrections.
Tire Wear: Bump steer can cause excessive tire wear, as the constant change in toe angle puts extra stress on the tires. Uneven tire wear not only decreases performance but will also increase tyre costs.
Inconsistent Handling: Inconsistent handling characteristics due to bump steer can make it challenging for drivers to predict how the car will behave in different situations. This can hinder their ability to push the car to its limits which will result in slower lap times or less aggressive drifting.
Eliminating or Adjusting Bump Steer
To eliminate or minimize bump steer, adjustments and aftermarket components are often required. Here are some ways in which aftermarket suspension products can help address bump steer issues:
Roll Centre Correction: Replacement uprights or knuckles with roll centre correction built in can help optimize the suspension geometry. By lowering the front roll centre and correcting the tie rod location to match, you can reduce the effects of bump steer.
Bump Steer Correction Kit: These are replacement outer tie rods which are specially designed to correct the geometry by raising or lowering the tie rod mounting location to effectively eliminate bump steer. The adjustable nature of these kits allows for fine-tuning based on the specific vehicle setup using shims or spacers.
Bump steer refers to the unwanted toe change that occurs when a vehicle encounters a bump and compresses the suspension system. This change in toe angle negatively affects the vehicle's stability and if excess can be outright dangerous. Visualize it as your car's tires both turning either inwards or outwards when hitting a bump as shown in the diagrams below.
Bump steer is directly linked to the suspension geometry, specifically the relationship between the lengths and mounting locations of the tie rod and the lower control arm. This is demonstrated well by the illustrations below which looks at the starting geometry for the bump steer above. You can see that lowering the lower control arm mount relative to the tie rod has cause an excessive amount of bump steer. In most cases OEMs design for a particular ride height, or even design bump steer into the suspension geometry, as a result when the vehicle is lowered this can cause increased bump steer.
III. Why Do We Want To Eliminate Bump Steer?
Bump steer has a few negative effects on the vehicle. Firstly, it makes the car extremely unpredictable whether that be at high speed and hitting a bump or simply going through a corner on a slightly bumpy racetrack. Instability is induced in the steering which is extremely dangerous and can catch inexperienced drivers out. Another affect that it can have is accelerating tire wear, impacting both performance and safety especially if the car is still driven on the road.
- How To Eliminate Bump Steer?
One of the easiest ways to adjust or remove bump steer is through changing the outer tie rod pickup point. This can be achieved with an adjustable outer tie rod kit that includes spacers to raise or lower the tie rod pickup point. As an example, below is a graphical representation of the bump steer on the GT86 chassis at OEM and -25mm ride heights. You can see that lowering the car surprisingly improves bump steer in this case. However, we get a much better by installing a GKTECH outer tie rod kit and using the 5mm shim so that the tie rod is mounted 5mm lower down, by doing this we almost completely eliminate bump steer.