crashing aint so bad
Join Date: Nov 2006
Location: santa barbara, ca.
Bike: 2005 red r6
Re: Speed Wobbles
If you get speed wobbles while off the gas and no hands on the bars, it's because you are off the gas. Not because of anything else other than a bump perhaps. Remember that the bike has rake designed into it for directional stability. But as with most sport bikes the rake is a fairly small amount. So the tire has very little directional stability in general. The only thing that really keeps the tire in line is it's inertia, hence the gyroscopic effect. Being on the gas unloads the front end allowing it to react in the manner in which it was designed, but also makes inputs easier to manipulate the tire. The grip from hell fights the natural movement of the tire over road imperfections. This in turn leads to a deflection in the opposite direction, which cycles and repeats.
When wobbles occur off the gas and with no hands on the bars it's very much the same thing. The difference is that instead of an opposing input at the bars, it's the weight transfer over the front tire that is exacerbating the issue. The front tire while decelerating becomes weighted down beyond it's static load. This adds force to the suspension and when a bump is hit, it reacts similar to holding the bars too tight. The tire deflects and is slow to react but once it gets moving, it moves too far in the opposite direction. The tire again deflects and is impacted by the road imperfections and the cycle repeats. In general having a light grip on the bars would eliminate that issue, also being on the brakes would again counteract the issue. Mostly because the energy would be transferred through the bike differently. While on the brakes the suspension goes through a major geometry change, making the issue become a different beast. This is why a bike is unstable ( usually while hard on the brakes ) and the rear tire will wallow around. Because so much weight is on the front tire, instead of it moving, the now lighter rear part of the machine moves and shifts under the inputs.
A good way to test this theory is to get up to a normal speed and let off the gas. Then let the bars go. Then with one hand give one of the bars a solid whack. The bike should go into a speed wobble. It should also quickly sort it'self out. Not an idea of fun, but you can do it on your bicycle as well.
The wobble is a needed and appropriate reaction from the machine. It will almost always work it'self out if allowed to do so. This is why it is said to let the bars go when one occurs. This is so you don't fight it. The speed wobble is not a bad thing, but it's not a good thing either. It is a needed reaction in order to deal with the problem that created it, but it is non productive to directional control too. There are two ways to eliminate a wobble. One is to let the bars go and or relax your grip on them. The other is to get on the gas harder to unload the front end even more and hopefully arrest the wobble. The later is difficult for beginners and is difficult to do on bike without lots of power. Even a 600cc machine can be under powered to deal with it with the second approach. The easiest way to reduce the potential for a wobble is to maintain a feather grip on the bars and remember to relax even more when one does occur.