Yesterday I went to the GYM with my bicycle. It was OK. After workout I found that the tire is completely flat! Today I used an air pump to blowing it again and see what happens. It was OK and I fully inflated it and ride to home about 3 mins. I checked it again and was OK. But after 5 minute it got flat completely in a second with a loud sound. This is the first time I see the problem and don't know the cause and how to fix?
2 Answers
Sounds like a faulty valve to me.
Not being funny, but the tyre is going flat because the air is coming out.
The two places air comes out of a tube are through a hole in the tube, or possibly a faulty valve.
You say it holds pressure for a while then suddenly lets go. This can happen when the hole is temporarily sealed by the sharp thing that made the hole, OR being pressed up against the inside of the tyre. Neither is a good seal, so after a bit the higher-pressure air gets past the thing holding air in, and you get a longer
"...---psssssSSSSSTTTTTttttt....."
rather than a "POP!"
Your best fix is to find the hole and fix it with a patch. Plenty of details in the link from Swifty on that.
If the air seems to be coming from your valve (your ear or fingers will tell you that) its possible to tighten the valve body. Exact details depend on the valve type, but Presta can be closed more with a small spanner or pliers if you're careful, whereas Schrader/car/AV valves tend to need a special tool.
You can do this - give it a try. The worst possibilities is you can't find the hole, and have to submerge the tube in water.
Last resort is to fit a brand new tube as long as you search the tyre for the cause. This costs significantly more than a simple patch; learning to patch is part of cycling.
If your bike has Tubeless tyres, then its way different.
