Bike Forums - View Single Post - Trueing a Wheel that is Slightly out of Round?
Old 06-23-09, 11:32 AM
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Originally Posted by jollysnowman View Post
Noob question + potential thread hijack (sorry in advance!): why?
This is a little OT.
The air pressure reduces the spoke tension. Most rear wheels have a significant tension differential from one side to the other due to the hub flange offset that makes room for the cassette. The differential will cause the dish to change a bit with the change in air pressure. Uneven tension on either side of a wheel can cause some lateral movement with a change in air pressure.
These changes should be fairly minor and how much change occurs will depend on how much air pressure is in the tire and how rigid the rim is and there are probably other variables.
My rims are light and I run 118 psi in my rear tires. I was surprised at how much the air pressure reduced the measured spoke tension, about one deflection unit on my Park tension meter. And the rim moved laterally about 1/2 mm.
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