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A little while ago my son's bike had a wobbly rear wheel. I tightened up some spokes which improved the problem but didn't remove it. Eventually I took it into my LBS who immediately diagnosed a problem with the bearings.

My question is whether a wobble caused by loose spokes looks different from a wobble due to a problem with bearings.

Thanks

Chris

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    If a wheel "wobbles" side-to-side as it spins that's usually due to spokes being misadjusted. (Note that the spokes are not loose, just not properly tensioned on one side vs the other.) If, with the wheel not spinning, you can grasp it and pull it a significant distance side-to-side then you probably have loose bearings. – Daniel R Hicks Aug 10 '17 at 0:21
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If you spin the wheel by hand with the bike off the ground, then side-to-side wobble is also called "out of true" and is caused by spoke tension, or an impact while riding. Wheel going badly out of true on final tightening

On the other hand, if you hold the non-spinning rim in your hand and move it left/right while mounted in the bike, there should be no play discernible or visible at the axle. If you feel motion sideways, then its bearings malajusted. How do I know if my cone/cap/bearings need to be adjusted?

A wheel can have both, or ideally neither, or either.

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If this is a "bicycle shaped object" from Walmart and such, with a thread-on freewheel (1970's design not seen on professional quality bikes, even at the entry level), the bike probably has broken rear axle. (Has the boy been jumping off things?) If the axle is broken, you can get a whole new wheel for that type of bike for some $30 US or maybe even less. This type of design uses a long, thin steel axle to connect the wheel to the frame. The rear sprocket cluster ("freewheel") screws onto the wheel hub and allows the axle to pass through it, but provides no support to the axle. Thus on the drive side, there is a lot of leverage acting on the axle. These axles tend to bend and break.

Or the axle cones could simply be too loose. On those bikes, you can tighten/loosen the bearing cones with a wrench. If they are too tight, the wheel doesn't spin freely; too loose and the wheel will exhibit side-to-side free play on the axle. There is a nice, bitter spot somewhere in between whereby the wheel exhibits no free play and still spins freely. You want to tighten it just a touch from there to pre-load the bearings (so the balls don't separate from the cone surfaces when the bike is under load). The people at the LBS would surely have diagnosed this, though.

  • It definitely could be a loose bearing. I'm in the same situation (BSO from Wal-Mart, wobbly rear wheel). Unfortunately I don't have the right sized wrenches to adjust the bearings. (If I could afford to take it to the LBS I wouldn't have bought a BSO from Wal-Mart.) – EvilSnack Aug 12 '17 at 15:02
  • @EvilSnack But a bike with a modern hub design wouldn't have this problem, so there would be nothing to go to the LBS for. – Kaz Aug 12 '17 at 15:09
  • Good point about the broken/bent axle. – Criggie Aug 12 '17 at 21:47

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