Bumpsteer Adjustment

BUMPSTEER Adjustment

Bumpsteer
is the amount a wheel will toe in or out when the wheel hits a bump, or when the suspension travels up or down.  It is measured in thousandths of an inch with a dial indicator that rides on a plate that attaches to the hub. 

One theory of bumpsteer is to stabilize the chassis as it goes around the racetrack. Another theory is that bumpsteer helps the car turn around the corner. Let's take a look at each theory so you can determine what bump steer really does. 

On the theory of bumpsteer stabilizing the chassis as it goes around the racetrack, this refers to both the straights and the turns. As the chassis goes down the straight away, it will go thru bumps and dips in the tracks surface. When the chassis does this, the suspension travels up and down causing the bump steer to take affect. To stabilize the chassis with this theory, the down travel of the chassis, or the up travel of the suspension, should cause the wheel to toe out. That way the chassis will wander less as it goes thru the tracks imperfections. Thus making the chassis feel more stable.

On the theory of bumpsteer helping the chassis turn around the corner, this refers to the inside wheel turning more than the outside wheel. This is a little trickier to figure out. This theory requires much research. If the track is flat and not much of a straight, then the inside wheel almost never travels into the compression state. If the track is like a drag strip with two hairpin corners, then there will be lots of initial compression travel and then none when the car gets into the corner. It will actually go into droop for most of the corner. If the track has lots of banking, then the inside tire will most likely always be in compression. On this theory, there is a lot of homework that needs to be done.


One of the main adjustments that affect the bumpsteer is the caster. When we change your caster, we will change your bumpsteer. This happens because when caster is changed, the mounting point on the steering arm from the spindle raises or lowers depending on which way you are changing the caster. This makes the arc of the tie rod to change, thus making the tie rods arc different than the spindle and making it steer when hitting bumps and dips. When we set your bump steer, it is relative to the spindles arc so when either is changed, the bump steer will change. So if we change control arm lengths, caster, or camber, these will all change your bumpsteer settings.

Let bumpsteer do its work. It is not designed to turn your car, but rather a side effect of all the rest of the suspension. The idea of bumpsteer is to not to let the wheels turn when hitting bumps or dips. Maybe the phrase should be bump no steer instead.

 

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