Stress Relieving Spokes Explained

by John Neugent

Tech articles | Commentary articles

John Neugent probably knows more about bicycle wheels than anyone else alive. Maybe more about bikes as well. He's spent his life in the bike business, at every level. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price. If you are in the market for a set of wheels, please, check out John's site. He really knows his stuff. —Chairman Bill

John Neugent

Bill & Carol McGann's book The Story of the Tour de France, Vol 1: 1903 - 1975 is available in print, Kindle eBook & audiobook versions. To get your copy, just click on the Amazon link on the right.

John Neugent writes:

Stress Relieving Spokes
There is a myth behind stress relieving spokes. Often, part of it is that it seats the spoke heads and nipples or that you need to go to extreme measures to properly stress relieve them. These go into the same trash bucket as believing that tighter spokes make a stiffer wheel and that thicker spokes last longer than some thinner spokes.

The primary reason for stress relieving spokes on a bicycle wheel is to prevent premature fatigue failure of the spokes.

Residual Stresses in Spokes

During the manufacturing process of spokes, various operations like cold forming the head, thread rolling, and bending introduce residual stresses in localized areas of the spoke. These residual stresses can approach or even exceed the yield strength of the spoke material.When the spokes are tensioned in the wheel, the tensile stresses from the tension add to these existing residual stresses. The combined stress levels in certain areas like the elbow bend and thread roots can now be very close to or beyond the yield point of the material.

Fatigue Failure Risk

Under normal cycling loads, the spokes experience cyclical tensile stress variations. Areas with stresses near or above the yield point have extremely low fatigue life and are prone to premature failure after a relatively low number of stress cycles.

Stress Relieving Process

To mitigate this risk, stress relieving is performed by momentarily over-stressing the spokes, typically by squeezing adjacent spoke pairs very tightly. This causes localized yielding and plastic deformation in the high residual stress areas.When the over-stress is released, the plastically deformed regions recover to a lower residual stress state, well below the yield point. This significantly increases the fatigue life of the spokes.The key reasons for stress relieving are to:

1. Relieve residual stresses introduced during spoke manufacturing
2. Prevent additive effects of residual and tensile stresses exceeding yield point
3. Enhance fatigue life by reducing stress levels in critical areas of the spokes

Properly stress relieving the spokes is crucial for building a strong, durable wheel that can withstand repeated cyclical loads without premature spoke failures.

John Neugent was was one of the first to establish quality hand building in Taiwan around the turn of the century. He now owns Neugent Cycling, a firm devoted to delivering world-class equipment at the lowest possible price.