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For some reason, my valve caps keep breaking. I'm not sure if it happens while I ride or while my bike is not in use, but often when I take the caps off to fill the tubes before riding, I find one of the caps has broken in half like in this image: tube cap broken in half

What could cause this?

Other info: I fill my tubes to 95 psi

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    @criggie I think it’s a presta cap – Swifty Apr 7 '19 at 6:27
  • @jay Whoops yes it is - sorry for the misidentification. – Criggie♦ Apr 7 '19 at 7:12
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You're simply overtightening the valve caps. These caps do nothing to keep the air in the tube, so there's no need to do them up tightly at all. In fact most road cyclists just throw them away instead of using them.

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  • Ok, thanks for the info! Why don't road cyclists use them? Seems like they're still helpful for keeping out dirt? – Jay Schauer Apr 6 '19 at 20:10
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    I haven't used them in years (10,000-20,000 km per year) and haven't once had an issue because of that. As for why roadies don't use them, like nearly everything else to do with road cycling, it's just tradition. It's even included in the Velominati rules of cycling as rule 60. – Carbon side up Apr 6 '19 at 20:17
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    The better question to ask is "why do these caps exist at all?" In the case of Prestia valves, it's because the valve tips are pointy and could puncture the tube when it's in storage. I don't know why they're used on Schraeder valves. – Adam Rice Apr 6 '19 at 22:16
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    @AdamRice On Schrader valves they make sense. They keep dirt from filling the void between the body and the core. When you fill in air the dirt will enter the tyre or worse, get lodged between the sealing surfaces, compromising the airtightness. – Carel Apr 7 '19 at 7:08
  • @JaySchauer: There is nowhere for dirt to enter when the Presta/Sclaverand valve is screwed down. If there is lots of dirt, simply push the valve in and let a puff of air clean it after unscrewing. – Michael Apr 7 '19 at 7:45

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