I've got a bike that hadn't been used in a while until a couple weeks ago, it was in a place where it gets direct sunlight (I'm trying to fix that) and as a result some things like the seat have spoiled.

Anyway, I inflated it just fine and have used it several times since then. About a week ago, another bike's tyre exploded (my guess is sun + overinflation); I spent a while trying to inflate that one to see if I could spot the rip, unsuccesfully and then just lt it be.

Since then, I've been unable to inflate the first bike's tyres due to major resistance (I guess the valve on the pump is not working properly)

Today, I was trying to inflate it before going out when I noticed there are bits peeling or being shaved off the side of the valve and I'm wondering whether this could be dangerous?

Valve peeling

Valve peeling 2

  • 3
    No biggie. There is usually a thin rubber/plastic coating on the outside of the valve, and yours got chewed up while being pressed through the hole in the rim. Commented Sep 28, 2020 at 17:27
  • 1
    The hole in the rim is likely to have sharp edges or burrs. Remove the tyre and the tube and de-burr the hole carefully with a triangular file or fine sanding paper.
    – Carel
    Commented Sep 29, 2020 at 11:05
  • "another bike's tyre exploded (my guess is sun + overinflation)" You’d need a lot of pressure. Most tires won’t explode even well above the maximum pressure printed on the sidewall.
    – Michael
    Commented Sep 29, 2020 at 12:49
  • @Michael, actually I doubt it was even overinflated. yeah it didn't even have much air; must have been around 50 psi (tire says 45-60); It was just resting against the wall with a Clug rack; I was using the PC, heard a loud noise and my dog came running in and when I went out I found the front tire completely flat. 🤷🏼‍♂️ Commented Sep 29, 2020 at 18:35

2 Answers 2


The type of damage shown is often due to under inflation or not centering the valve stem in the hole. When under inflated the tube doesn't exert enough pressure on the tire bead. This allows the tire to spin on the rim. That in turn causes the tube to shift pulling it at an angle and chaffing the valve stem.

  • That would make sense considering; as I say, that they hadn't seen much use recently. Thanks. Commented Sep 29, 2020 at 18:36

It looks to me as though the pump head, the part that attaches to the tube, is damaging the valve stem of the tube. Personally I wouldn't worry much about some minor scuffing and gouging, as shown in your second picture, but when pieces start flaking off, as in your first picture, then I'd replace the tube, because it looks as though the valve stem might fail.

If the valve stem fails then the result will be a "blowout", meaning that there will be a loud bang and then you won't have any pressure. If you're riding at the time then you can do damage to the tire (or tyre if you prefer). In the worst-case scenario, a blowout could result in a crash if you were cornering at the time.

I don't think I've seen damage like that before. I would suspect the pump head first, especially since you reported trouble with it. Maybe you aren't using the pump correctly; the lever on the pump head is meant to be flipped one way to grip more loosely when you're pushing the pump head on the valve stem, and then flipped the other way to grip tighter when the pump head is in place. If you are not using the lever at all, or using the lever incorrectly, that may be part of the problem. With most pumps these days the lever is parallel with the rim to put the pump head on, and perpendicular to the rim to lock the pump head in place.

If the pump head is the problem, most bicycle shops will be able to sell you just the replacement head, which is cheaper than an entire new pump.

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    If the pump head was causing this then the marks would be farther out on the valve stem. And try taking a knife and cutting off the stem -- you can't, because there's solid metal under the rubber. Commented Sep 28, 2020 at 17:58

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