Saturday, July 11, 2009

Spoked Wheel - Part 3 - Fatigue Cycles

How many revolutions should a wheel last (need for fatique calcs)? Infinite is great of course, but what is reasonable? 10-20 years ? Rim-braked rims wear thin of course, so... For now I will go with15 years. Say 25 miles per day. 9125 mile per year. 210 cm (0.00130488 mile) circumference wheel (700x23c). 9125 miles/0.001305 miles per revolution = 6,992,882 revs per year or ~ 7 million wheel revolutions per year.
In 15 years, 105 million revolutions.

For a racing wheelset: 2 or 3 races a month, maybe 200 miles for 9 months a year. 1800 miles a year. Keep only 5 years. 6-7 million wheel revolutions.

However, typically the knee for fatigue life or endurance limit for steel is right around 1 million cycles. In other words, if the steel component being dynamically stressed doesn't break after 1 million stress cycles, it probably will have infinite life.

One issue is that Aluminum does not have an endurance limit.
Summary: Wheels see enough stress cycles that they should be built for infinite life.