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Bump Steer?


BrianEb

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Apparently you dont race Monkey boy.

 

As a motocross racer myself, I completely aggree with sredish 100%.

 

I have a set of +2+1 TRC a-arms for my banshee with 10 inches of travel and the bumpsteer caused by the suspension travel is not that much.

 

Last week i raced at thunder ridge which is about a mile down the road from Unadilla. If anyone has ran at either of these tracks, they know about the potholes that form at both tracks. Now i dont have a steering stabilizer so i know how bad potholes cause bumpsteer, because what happens is that when you hit them, one tire is going on flat ground while the other gets jarred by the pothole. When you hit something so harsh it tends to send a lot of feed back through the handle bars which contributes to massive arm pump.

 

By putting a steering stabilizer on anything, it takes the shock felt through the handle bars from hitting pot holes and what not, and reduces it greatly. I would know because i have ridden other quads equipped with stabilizers. Now even though the predators are designed to eliminate bumpsteer caused by suspension travel, they are still prone to bumpsteer caused by pot holes and stumps and what not. So even the "zero bumpsteer predator" can gain benefits from the addition of a steering stabilizer.

 

I'm no expert suspension specialist but i do race and know what works. So if you dont want bumpsteer, keep the travel around 10 inches, get a stabilizer, or just ride flat tracks and roads.

Edited by Wassup350
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OK, let's start at the beginning.

 

I do race. I won't bust out my resume here, but I'm not pro class.

 

I understand what you are saying, and I am completely agreeing with the need for a stabilizer. I have one on my Kawi, but not the Banshee as it isn't always needed in the dunes. I don't see where it was taken I disputed the stabilizer need. Every quad ridden faster than 5 mph should have one.

 

What I disputed was the idea that bump steer includes trail ruts.

 

I understand that they cause unwanted steering input, and arm pump, I just don't agree that it falls under my definition of bump steer. It's trail obsticals to me.

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Jesus H Fuckin Christ! How fucking hard is it for people to comprehend how bump steer works in relation to objects you hit on a trail/track/road/what ever

WTF do you think is going to happen when you hit an object with one tire?

 

This was taken from a website to describe how its caused and what it does

A. Definition

 

Bump Steer is when your wheels steer themselves without input from the steering wheel. The undesirable steering is caused by bumps in the track interacting with improper length or angle of your suspension and steering linkages.

 

Most car builders design their cars so that the effects of bump steer are minimal. However, you must still take care to bolt on your suspension carefully so as not to create unwanted bump steer. Make sure that you are always using the correct components for a particular car. Bump steer must be designed into the car and cannot be adjusted out if improper parts are used or if pivot points are moved without considering bump steer design principles.

 

In order to accomplish zero bump the tie rod must fall between an imaginary line that runs from the upper ball joint through the lower ball joint and an imaginary line that runs through the upper a-arm pivot and the lower control arm pivot. In addition, the centerline of the tie rod must intersect with the instant center created by the upper a-arm and the lower control arm (See diagram below).

 

The instant center is an imaginary point that is created by drawing a line from the upper a-arm ball joint through the a-arm pivot where it is intersected by an imaginary line that extends from the lower ball joint through the inner control arm pivot. Where the two imaginary lines intersect is the instant center.

 

Sounds complicated? Really it is very simple. To achieve zero bump the front end must be designed correctly. The tie rod must travel on the same arc as the suspension when the car goes through travel. Simply matching lengths and arcs to prevent any unwanted steering of the front tires.

 

To exaggerate, if the tie rod were only 10" long and the suspension were 20" long then when the suspension traveled the tie rod angle would shorten much quicker than the suspension arc. In this scenario the tie rod would shorten much quicker through travel than the suspension and the car would toe in drastically over bumps. The shorter arc of the tie rod would pull on the spindle and toe it in through travel.

 

Bump Simplified - When designing a car, if the centerline of the outer tie rod lines up with the centerline of the lower ball joint, and the inter tie rod lines up with the lower pivot point then the length and angle of the tie rod and suspension will be the same resulting in zero bump. Most car builders design their cars in this fashion.

 

 

Check out google if you want to see what it is http://www.google.com/search?hl=en&q=bump+steer

There is even a link to a program on how to eliminate it. Its mainly for automobiles but also works on anything w/ 4 wheels.

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I think of bump steer as when you wheels are going where your bars arnt pointing ie you have absolutely no controll over it. When you hit a bump your bars turn too...you *can* controll it with a damper and bigger arms....but i can see how getting the bars jerked could be considered bump steer

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