bump steer?

[Fast350ex]

What is bump steer? Lots of people refer to this word when they put 400ex a-arms on a 300ex. It would help if I knew what this word meant.

[Juggalo]

its when your wheel toe moves in or out as the suspension moves through its travel

when your handlebars go side to side

[cdalejef]

In a nutshell, its when you hit a bump or obstical and your bike wants to change directions on you.

[SnellCRP]

The technical definition of bumpsteer is a change in toe angle caused by the suspension moving up or down. Bumpsteer is built into the geometry of the suspension and steering system, and has nothing to do with turning the bars. The effect of bumpsteer is for the wheel to toe-in or toe-out when the suspension moves up or down. This toe change or “steering” occurs any time the suspension moves, whether it is from body roll, brake-dive, or hitting a bump on the track. Bumpsteer is undesirable because the suspension is steering the quad instead of you.

[Fast350ex]

thanks guys.

Why does this happen with 400ex a-arms on a 300ex, even if you have the right suspension?

[300exOH]

bumpsteer occurs because the positioning of the a arms and because the spindles are very different. It puts the tie rods in an odd angle which gives the suspension leverage to move the bars.

[SnellCRP]

The front wheels do not move directly straight up or down when the quad hits a bump. Instead, the wheel follows an arc, or curving path, that pushes the wheel slightly inward (towards the centerline of the quad) or outward (away from the quad) in response to vertical wheel movement. The outer tie-rod (which connects the steering stem to the spindle) also moves in-and-out in an arc as it moves up and down. If the rate which the outer tie-rod arcs in or out does not match the rate the wheel moves in or out, the wheel will be turned by the tie-rod. This is bumpsteer. The center point of the arc traveled by the wheel (known as the instant-center) is controlled by the location and angle of the moving suspension links. This point moves as the ride height changes. In contrast, the arc of the outer tie-rod is controlled by the position of the steering stem, which is fixed.
In order to eliminate bumpsteer, both the length and the center point of the two arcs must be the same. However, since the instant center moves with ride height, bumpsteer cannot be eliminated throughout the entire range of suspension travel. Therefore suspension designers will concentrate on minimizing bumpsteer within the range of movement closest to the desired ride height. It wouldn't have to be perfect at full compression or at full droop only as close to perfect as you can possibly get at the desired ride height. Hope this clears some of this up for you.;)

[300exOH]

Excellent explanation SnellCRP. That's what I was getting at.:o

[SnellCRP]

This kind of conversation is a blast for me. I love talking tech stuff.:macho