What is bumpsteer?
The term bumpsteer refers to the steering angle of a wheel changing when the suspension compresses, mostly due to a bump. More generally, having bumpsteer means that your steering angle changes through the suspension stroke. The effect is mostly noticeable on bumps, as this effect happens without you having much control (as opposed to eg. a natural behaviour during roll in a corner). It results in the car being thrown off course due to a bump, or behaving quite erratically on uneven surfaces.
As you see, we are referring only to the change of the steering angle and not the camber angle throughout the suspension stroke, although they can affect each other depending on the geometry setup.
Checking for bumpsteer
Although often quite noticeable on the track, you can easily check for bumpsteer on your RC car. Two things:
- You can press down on your car to compress the suspension.
- You can disconnect the shocks and move your suspension arm throughout its range.
If the toe-in / toe-out / steering angle of the wheel changes throughout the compression or suspension stroke, this means you have bumpsteer.
Is bumpsteer bad?
Well it depends on what you want. Generally you want zero bumpsteer, but it depends on how your car actually behaves. Some cars have a bit of bumpsteer as standard to counteract for example being thrown off course a bit through bumps. But generally, if you want a predictable car then cancel out the bumpsteer.
Altering the bumpsteer on the Lazer ZX range
The original Kyosho Lazer ZX had a straight steering plate LA-17 while the Lazer ZX-R has an angled steering plate. The angled steering plate has a different effect on the different between the steering angle of the inside wheel versus the outside wheel when cornering. Many racers however preferred the straight steering plate of the ZX as the geometry had less (impact on) bumpsteer throughout the steering angles.
Normally, you can tune out or reduce the bumpsteer by altering the position (higher / lower) of the steering rod pivot balls. On the Lazer the position of the inner pillow ball is below the steering plate while the position of the outer pillow ball is above the knuckle. This means screwing any of the pillow balls out always has the same result. Some racers repositioned the inside pillow balls above the steering plate with either a longer steering rod (at an increased angle) or with longer threaded outside pillow balls with spacers to have more control over it.
Note that the bumpsteer can be affected by the castor angle (front-to-rear angle of the front suspension), which means your bumpsteer can change when you switch from the LA-27 to the LA-59 (using the inner extra castor holes) or for example the Teamline hubs.
