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After about almost two seasons of regular city riding, I had the good judgement to roll over some still-hot asphalt, resulting in a puncture in my rear tube.

While this is the first time I've had to replace a tube on this particular bike and these particular rims, I followed the standard procedure I've used dozens of times on other frames over the years:

  • I removed the rear wheel;

  • I popped off the bead on one side of the rear tire;

  • I fully deflated and removed the old tube and disposed of it;

  • I finally put in the new tube after checking that the rim tape's in good shape, taking care not to pinch it between the tire and the rim.

After inflating the new tube, I noticed that the tire was rising up and away from the rim right where the valve was.

I deflated the tire and jiggled the valve around, making sure that the threads (it's a Presta) weren't getting stuck on the rim, but the valve wouldn't come out any further. I decided to make the short commute back home, since worst case, I could always walk.

Biking into work the next day, I managed to get a slow leak meaning that my tire was flat by 10 AM after riding in, with the puncture being right next to the valve. After replacing the tube again, I've once again got that weird bump.

I'm sure that my tube and rim have the right width; both are 700x23c (the tube is advertised as 23-25c on the packaging). I haven't yet had a flat on the newest tube, but I'm extremely hesitant to keep riding with my tire in that shape.

This is also the first time I've replaced a tube on a deep dish rim; are the steps and checks any different?

What causes this weird bump, and what can I do to avoid it?

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Usually this happens when the thick, reinforced part of the tube surrounding the valve is stuck underneath the tire bead rather than the tube being fully enclosed by the tire. The tire then can't seat quite right at that spot and rides high. Usually the fix is to deflate the tire, temporarily remove the Presta nut if present, grab the valve and shove it up into the tire, pull the tire to each side all the way around but especially at the valve to check that you can't see any tube protruding from the tire (you should always do this when changing a tube/tire), and then re-inflate.

Riding a tire like this is pretty dangerous because sudden blowouts can result from the tube not being properly constrained inside the tire.

The rim being deep doesn't cause this per se, but many deep rims are also on the narrow side, which will contribute to it happening.

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