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A perfectly round wheel???(5 posts)

A perfectly round wheel???VictorChan
Aug 2, 2001 9:36 PM
Just have a question. Is it normal to have the wheel kind of swinging up and down? Like the rim is kind of going to the oval shape? On my rear wheel, while spinning it freely, I "felt" the frame kind of moving up and down in a very hardly noticeable way. However, the frame does move when I pedal the rear wheel to spin very fast in the 26 mph range. Visually, the rear wheel looks round. My theory is that maybe the tire is not evenly inserted or parts of the tire is heavier than the rest. Using a pair Michellin Bio Sport tires. I really want to eliminate this slight frame movement if it is possible.

re: A perfectly round wheel???Jofa
Aug 3, 2001 2:16 AM
This effect is usually caused by the weight of the tube valve putting the wheel slightly out of balance. Older rims used a plug at the join, instead of welding, which generally countered this imbalance. Modern rims with machined sidewalls are more prone to uneven weighting as well, as the machining causes inconsistent sidewall thickness; and tubes and tyres aren't usually made to tolerances so precise.

In any case the effect is academic and only observed when you spin the wheel up to speed by hand, and is entirely imperceptible whilst riding. If you are feeling uneven movement when riding then it's attributable to something else... probably the spinning of your legs.
re: A perfectly round wheel???VictorChan
Aug 3, 2001 5:22 AM
Is the rim perfectly concentric with the hub?Donut-Boy
Aug 3, 2001 12:50 PM
Not exactly sure about this, but couldn't a crummy build or truing move the rim so that it is "true" but not concentric...causing a real bounce...? You would be able to observe this by using your brake pads & frame as a makeshift truing stand and looking for the bounce as you spin the wheel. I could not tell from your post if you had already done this yet.
Is the rim perfectly concentric with the hub?VictorChan
Aug 3, 2001 1:31 PM
I did but nothing looks too weird. The bounce is a "felt" thing on the frame. Very slight movement. Too bad I don't know how to recenter the wheel or rebuilding a wheel. Otherwise, I would redo them both.