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The rim of my bicycle seems to be out of round.

I took a video of the rotating rim. As you can see from the video, the tire is a bit bumpy.

I used to suspect the problem comes from the tire. But I bought a new tire and replaced, the problem still exists.

The video was taken for the new tire.

What is the problem with the rim? What tools do I need to diagnose the problem?

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    You should go to a LBS (local bike store) and ask them. Most will tell you honestly if you need to replace or repair. Proper tools to perform a single repair are more than the cost of the repair. A proper repair is like $15-$25 USD. – paparazzo May 15 '17 at 21:20
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    The video is a bit hard to see. Taking a video along a direction perpendicular to the axle of the wheel will make it easier to get some idea of whats going on. – Batman May 15 '17 at 21:26
  • The video is hard to interpret. Until someone with more patience writes an answer, read one of the many online guides to wheel truing and start there, or go to LBS. – whatsisname May 16 '17 at 6:50
  • @Paparazzi I went to one LBS and the guy managed to fix the problem by 1) deflate the tire 2) put some kind of "lubricating foam" around the outer tire 3) pump the tire. I didn't observe the steps closely so I might be wrong. Any idea on what that "lubricating foam" is and why it fixes the problem? Or did I just seat the tires inappropriately? – xiaohan2012 May 16 '17 at 17:52
  • Sounds like the tire just did not set properly. I was hard to tell from the video. You can just use diluted dish soap for "foam". . – paparazzo May 16 '17 at 17:55
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The proper way to ensure your rim is 'true', is to remove it from the bike and put it into a 'truing stand'. A truing stand allows you to precisely measure a rim's "lateral runout" (side-to-side wobbling) as well as "radial runout" (a.k.a. "hop" - this is where the outer circumference of the rim is uneven in its distance from the center of the hub). If the truing stand reveals any issues, you would likely need a 'spoke wrench' to appropriately tighten/loosen the pertinent spokes to correct the problem (you'll need to read-up on these techniques as well spoke tension and general wheel building ).

Since wheel truing is a fairly involved process that requires significant time, patience, knowledge, and some experience, it might be wise to first make sure you have definitely ruled-out an issue with the inner-tube or tire. Remove the tube and tire. Ensure that the wheel is clean and dry. Ensure that the inner-tube is clean and dry (lightly powder the tube if needed). To ensure that it's not twisted or kinked, inflate it just to the point that it holds its shape. Then carefully nest it into the tire and carefully put the tire onto the rim. The trick here is to ensure that there is no friction or encumbrances to the tube and tire taking an even/uniform shape as they're inflated to pressure.

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