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REAR WHEEL FACTORS
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Multi-speed rear wheels like to go out of true for several reasons that are related to the wheel driving the bike and the uneven dishing. The stress cycles of driving the bike are added to the stress cycles of carrying the weight of the bike, hitting bumps, and braking. The driving stresses can be greater than the basic riding stresses, and the harder you pedal the larger these stresses become. When you combine the drive torque stress factors, the general stresses from being ridden, and the uneven spoke tension and lateral strength factors, a rear wheel can have trouble staying in true. Spoke preps help this situation by setting up after the wheel is built, but a properly built wheel is always better than a poorly built wheel that has been 'glued' together. Since half of the spokes (or a fourth in a half radial lacing) are responsible for driving the bike, the 'pull' spokes, they are constantly having great stresses applied and relaxed from the drive torque cycles. The spokes that do not transfer the power, the 'push' spokes, have their build tension relaxed and then reapplied from the drive torque cycling. The 'push' spokes drive stress cycling isn't as sever as the 'pull' spokes drive stresses. The stress cycling factor on the 'pull' spokes causes them to age faster than the other spokes ('push' and front wheel), and the wheel will not hold true after a few thousand miles. The aging of the 'push' spokes reduces their strength, and that results in their stretching. The drive torque stress cycling and aging are the reasons why drive side spokes are the ones that usually break. In a multi-speed rear wheel the drive side spokes are tighter than the non drive side spokes in order to achieve a true wheel with dish offset. The drive side 'push' spoke tensions come closer to their maximum load capability due to the increased stresses from the drive power cycles. Drive side spokes also age faster than non drive side spokes due to the increased build tension. When you combine their decreased strength from aging, drive torque stresses, and road shock stresses, instantaneous shock stresses overload the drive side spokes and cause them to fail.
Generally non drive side spokes in multi-speed rear wheels are the ones that cause the wheel to go out of true. The non drive side spokes are laced with much less spoke tension than the drive side. The 'push' spokes on the non drive side can easily have all of their build tension removed due to drive torque stresses. When the tension cycles back to normal, the nipple can unscrew a little. The lower the build tension worse the problem becomes. The greater the build tension the higher the resulting tension on the spoke threads, and the harder it is for the nipple to unscrew from the stresss. This is revealed during building a wheel, the tighter the spoke becomes the harder it is to turn the nipple.
Rear wheels that are poorly built are more suseptable to the effects of the stress factors and go out of true quicker and easier. A poorly built wheel has tight spokes and loose spokes spread all around the wheel. All of the stresses from riding and propelling the bike make it easier for a loose spoke to unscrew from the nipple. This problem is also more likely to happen on poorly built rear wheels than porly built front wheels.
In rear wheels with no dish offset (such as single speed) the spokes on the different sides of the wheel see equal stresses, like front wheels. Properly built drive wheels with no dish offset do not suffer as easily or severly from the problems just described. All ridden wheels will eventually fail due to the stresses involved in ridden a bicycle.
The problems of the uneven spoke tensions on multi-speed rear wheels lead me to develop lacing patterns that would counteract this imbalance. This resulted in the 2-cross/3-cross and half Crow's Foot rear wheel lacings that I have been using on my personal bikes. These lacings and the half radial lacing are discussed more in the STRONG REAR WHEEL LACING chapter.
