Thread: Rim Bulge
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Old 08-28-25 | 07:51 PM
  #10  
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sweeks
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Bikes: Airborne "Carpe Diem", Motobecane "Mirage", Trek 6000, Strida 2, Dahon "Helios XL", Dahon "Mu XL", Tern "Verge S11i"

Originally Posted by cyccommute
I’ll add to check the sidewall of the rim for concaveness as well. Put a straight edge on the rim from the top to the bottom. If the rim is okay, the sidewall should touch the straight edge from top to bottom. If the rim is worn, you’ll see a gap in the middle.
This ^^.

The shadow of the edge of this ruler illustrates the extent of the convexity of the rim flange due to brake wear.
The shadow of the edge of this ruler illustrates the extent of the convexity concavity* of the rim flange due to brake wear.
*Thanks to OneClick for catching my stupid typo.

Also...
When the wear makes the flange thin enough, tire pressure forces it outward. Brake application presses it back. This back-and-forth flexing eventually causes the alloy to crack. At this point, the rim will begin to
When the wear makes the flange thin enough, tire pressure forces it outward. Brake application presses it back. This back-and-forth flexing eventually causes the alloy to crack. At this point, the rim will begin to "thump". Bad things can happen if this wheel continues to be ridden. (This is a 20" wheel with an internally-geared hub, which is why the spokes appear to be at a goofy angle.)
Last edited by sweeks; 08-29-25 at 08:42 AM.
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