Front End Wobble


7 replies to this topic
  • CodyWayne718

Posted November 06, 2011 - 06:10 PM

#1

What is it usually from? Fairly smooth dirt and when I got to 4th thru 5th the front end would go crazy. Not every time but I'd say 75% of the time on this particular straight. Could it be my stance? Jus not sure why it's not all the time at those speeds.

  • ronbuell

Posted November 06, 2011 - 06:15 PM

#2

Loose steering stem or wheel bearings, check both.

  • RiderX

Posted November 06, 2011 - 06:24 PM

#3

It sounds like he's talking about head shake, not play on the steering stem or wheel bearings. If so you need to first check your sag and make sure your springs are correct for your weight. Headshake is usually caused by improper sag. :busted:

  • grayracer513

Posted November 06, 2011 - 07:54 PM

#4

Head shake can be caused by any factor that will cause incorrect steering geometry, or by a lack of damping at the steering head, front tire off center, or by uneveness in the road surface, and a number of other things. The five most significant things that influence head shake have been found by engineering studies to be lateral stiffness of the front tire, steering damping, height of bike center of mass, location of bike center of mass between the wheels, and the cornering stiffness of the front tire.

Something gets things rolling by deflecting the wheel off center. The tendency of the steering geometry to center up the tire quickly corrects this, but without adequate damping the reaction swings the tire back to center and beyond in the opposite direction. A cycle of oscillation is setup that either holds at some level of intensity, or increases until control is lost.

Unless something is actually wrong, like an off centered wheel, misaligned rear wheel, loose bearings, etc., the best cure is a steering damper.

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  • jratcliffe3

Posted November 07, 2011 - 01:13 AM

#5

Positioning on the bike also helps. Fast straights like this, you want the front wheel as light as possible to reduce the chances of what gray described from kicking off - less weight means lower forces, so the chances of getting into a tank slapper are lower.

Stand on the pegs, and hang your arse over the back fender, keep the throttle pinned all keep the front wheel light at this speed. That is probably why it is not all the time - if you are not riding consistent and letting the wheel drop into a hole sometimes, this might be when you are getting the wobble.

  • grayracer513

Posted November 07, 2011 - 08:22 AM

#6

Positioning on the bike also helps. Fast straights like this, you want the front wheel as light as possible to reduce the chances of what gray described from kicking off - less weight means lower forces, so the chances of getting into a tank slapper are lower.

Stand on the pegs, and hang your arse over the back fender, keep the throttle pinned all keep the front wheel light at this speed. That is probably why it is not all the time - if you are not riding consistent and letting the wheel drop into a hole sometimes, this might be when you are getting the wobble.

The reduction in the tendency to wobble from tactics such as you describe is more than likely the result of the front fork being more extended and thus having more head angle. In fact, moving the center of gravity forward toward the steering head is one of the most effective ways of dealing with head shake, although it often works contrary to what you're trying to achieve with handling overall.

Moving the CG forward works by reducing the leverage that forces acting on the steering head have on the yaw axis of the chassis. (Yaw is the rotation of the chassis to the left or right around an axis that runs vertically through the CG). With the CG farther forward, it's just that much harder for the oscillating fork to push the steering head from side to side, and the bike's own mass tends to damp out the wobble. Once again, however, this is not always a practical solution.

It can also depend on the surface being traveled. In a heavily tracked sand wash, for example, the front tire will try to follow every track it finds in whatever direction they run. The cure for me is to move forward on the bike to force the wheel a little deeper into the surface where the previous tracks are less of an influence.

  • CodyWayne718

Posted November 07, 2011 - 10:27 AM

#7

Awful lot to take in! I'll check my rear wheel alignment since that's the only thing I've tinkered with. If all else fails, guess I'll put a stabilizer on my wish list. Thanks

  • grayracer513

Posted November 07, 2011 - 01:22 PM

#8

Also check to see if the front wheel is centered between the forks, and that the head bearings are adequately tightened. If your forks are all the way up in the clamps, check the sag, as recommended earlier. It's not very likely that you would have too little as a result of wear, though. It's usually the other way around.





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