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When riding, the rear wheel feels as if there is a tiny pebble, stuck within the thread.

The wheel is one week old, the hub is Shimano FH-M475. I have done only very tiny jumps - for example from curbs, but could have landed badly a few times i.e. directly on the saddle. I am 70kg (154lbs).

I don't have rim brakes, so I can't determine if the rim is bent. However,visually, it is fine. My rear tire runs at 4.5 bar (65psi).

Is the axle bent? Is it my fault or can I claim warranty?

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  • Does the wheel spin true or is there any sideways or up and down movement? Is there any noise coming from the hub? Sounds more like a rim flat spot or buckle to me. Generally if it's a hub issue you should be covered by warranty, if it's a rim you won't be. It's a cheap hub, but it's good value and unlikely to fail through a low impact jolt like a jump
    – DWGKNZ
    Commented Mar 2, 2014 at 10:58
  • I'd first look at the wheel and rim. Spin the wheel and sight the outer edge of the tire from the side. Does the tire move up and down? Also look at the rim -- is it perfectly circular or is it moving up and down? Sometimes this problem is just a poorly seated tire. (If the axle were bent you wouldn't feel a regular bump.)
    – Daniel R Hicks
    Commented Mar 2, 2014 at 13:10
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    Understand that when the wheel is turning on the bike, the axle is stationary, and always maintains the same orientation to the ground. Thus, even if there were a fault of the axle itself, it would present if a continuous problem, not a "bump" with every revolution.
    – Daniel R Hicks
    Commented Mar 2, 2014 at 23:04
  • bend axles are easy to identify, they feel like loose cone's. if you can wiggle the axle in the hub try tightening the cones, if they feel loose again after spinning the wheel on the axle then you can say it's for sure a bent axle.
    – BrianC
    Commented Mar 3, 2014 at 19:56

2 Answers 2

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To my mind, a 'feeling like a small pebble' suggests something in the hub itself, perhaps a failing bearing. To test for bearing damage, hold the axle in two hands and spin on he wheel. See if you get a regular catching feeling that would suggest a damaged bearing or bearing surface.

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    And if it feels like this - STOP RIDING IT - until it gets fixed. You could damage the hub cups, which likely cannot be replaced (you'll have to replace the hub).
    – Benzo
    Commented Mar 4, 2014 at 14:30
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Can't really comment on whether it's your fault or not, or whether the warranty applies. I'd say take it back and try. Only way to find out...

Now onto actually doing it yourself, if you were so inclined. Taking apart a hub is pretty easy and straight forward. The only specialty tool you need is a cone wrench, which is just a really slim wrench, to get into the cone-nuts. Knowing about the concept of a locknut is important here. There will be a 17mm nut locked to a 15mm cone nut on the shimano hub you have, so you'll need a normal 17mm wrench as well.

If you're working with a rear hub, you want to undo the nuts on the non-driveside and pull the axle out, leaving the driveside nut-cluster in place. For a front hub, you can remove either side. Be careful, as bearings will be exposed and can spill out. You can then inspect the axle to make sure it looks good. Also inspect the amount of grease in the bearing races, and you can inspect the races for pitting or wear also.

I've seen bearings split, dirt get in, axles break, and cone nuts get loose, among other things. Any of these issues could cause your current problem.

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