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THE KEY STARTING POINT
A necessary foundation for good handling is proper frame and chassis alignment. Identifying the cause of poor handling conditions can be tricky. This section covers

HOW to recognize a misaligned frame and chassis component
WHERE the problems are
WHEN to have the chassis components checked for misalignment
WHAT is the probability of a chassis component being out of alignment?
WHY check frame and chassis?
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Some key factors for determining if it's frame or chassis damage, and a definition of some terms:

1. Pull — Bike tends drift in one direction or the other
A common complaint is that the bike turns great in one direction but won’t turn worth a damn in the other. This forces the rider to compensate by counter steering — applying more steering input on one bar than the other. In some cases, the rider then has to shift riding position off the bike’s center of gravity to maintain a straight line. If you removed your hands from the bars (not recommended) the bike would dive/pull in one direction.
So what causes this condition? This can be caused by one or more chassis components being misaligned. On a list of things to check, the top item would be a twisted/bent steering head. (The center line through the frame’s steering head). A bent or misaligned swing arm would be next on the list. A key indicator for a misaligned swing arm would be excessive chain and sprocket wear. Also a misaligned subframe could be a factor causing the rider’s weight to shift off the center of gravity. Other things to look for would be bent fork legs in the front suspension, and bent or twisted triple clamps. Another indicator of misalignment could be irregular tire wear.

2. Push When a bike understeers through a corner
The front wheel loses gripping contact with the road surface causing the bike to run wide. This can happen entering, during, and exiting a corner. One of the causes for this condition may be excessive rake or caster angle. Example: if your frame’s spec rake angle calls for 25 degrees of caster but your frame’s steering head angle is 30 degrees, this will cause a bike to push. This condition will also cause the bike’s steering to be heavy and slow. This may or may not occur in both directions. If it happens in only one direction, there is likely to be a twisted centerline in the frame’s steering head. If it occurswhen turning both directions, it is probably not twisted, but is as described above.

3. Wobble and Weave — Instability of the steering head causing either high or low oscillating frequencies ( gyro effect)
Weave is a low frequency large gyro condition. Wobble is a high frequency small gyro condition of the steering head. Example: a good comparison for wobble is a shopping cart’s front caster that wobbles. This condition may be associated with a misaligned steering head, in which the rake/caster angle is too steep. Example: Your bike frame’s rake/caster angle spec is 25 degrees, but your angle is now 20 degrees. This condition also causes steering to be light and excessively quick, making the bike unstable in a straight line.
These are just some of the main causes of the above described conditions. There can also be many other factors that are not described in this section. They may not necessarily be related to a misaligned frame or chassis component. But remember, to get the best handling characteristics from your bike, first eliminate any possibility of a bent or misaligned frame/chassis component.


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