Today I was trying to pump my bike tire using mini pump. It has presta valve and after pumping i found that I've bent the valve core by about 5 to 8 degree angle. I tried to bend it back enough for it to be somewhat straight. My question is, should I replace the core? Should I be worried?

  • You carry a spare tube anyway, right?
    – Criggie
    Commented May 10, 2017 at 22:32

3 Answers 3


It happens, especially if you remove the pump head not perfectly vertically or you move the pump head while pumping.

You can avoid this by using a bit of hose on the mini pump like on this mini pump enter image description here

or bracing the head of the pump while pumping.

Its not the end of the world if the valve core is bent -- I've run tubes for years with slightly bent valve cores. Note that at some point it may break (and you'd need to get a new tube then). The presta valve only lets out air when you press down on the valve core, which you can't do once you tighten down the nut (even if it doesn't sit flush with the rest of the valve and hits the stem at the angle, you can't push the nut down anyway to let out air).


I wouldn't worry about it. Repeatedly bending the core could cause it to break, but as a one-off, it should be fine. I quite often end up with slightly bent cores, and don't normally bother bending them back, and I don't recall ever having a valve fail.

  • 2
    The core is made from brass and rather soft. Bending happens easily. If the valve can still be closed I would not try to bend it back which could break it off. But I'd carry a spare tube in my pocket.
    – Carel
    Commented May 10, 2017 at 14:57
  • A Guaranteed way to break the stem is to try and unscrew the acorn nut completely. It doesn't come off because most manufacturers have a subtle flair on the end to stop you doing this by accident.
    – Criggie
    Commented Nov 15, 2019 at 9:58

At some point when you replace the tube, get one with a shorter valve. Prestas come in different lengths to accommodate different rims and some (like for aero tires) are way too long. A larger bike vendor will have a better selection of sizes.

  • Though, unfortunately, most shops only carry one or two valve lengths in many tube sizes, Commented May 10, 2017 at 16:41
  • 1
    Thus my suggestion of shopping at a larger vendor for this kind of thing
    – RoboKaren
    Commented May 10, 2017 at 17:02

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.