How to Repair a Mountain Bike Tire Puncture

The main type of puncture that occurs on mountain bike tires are impact punctures. These punctures, also known as "snakebite" punctures can be dangerous. A sudden front tire puncture at high speed usually causes a disastrous loss of control which is a good reason for keeping your speed on steep downhill's. Snakebite punctures are caused by the inner tube being pinched between the tire and rim when the tire bottoms out against the rim as it hits a rock or other obstacle. They leave a characteristic double hole in the tube, hence the name. They can be prevented by keeping tire pressures fairly high, or also by using the fattest tires you can fit into your frame.

If the flat was very slow, the cause may be a very fine piece of wire or a thorn. If you can't find the reason for the flat, there are only two ways to cure it. Either replace the tire, or spend as long as it takes to find the offending object by going over the tire with a fine tooth comb. A bright light helps, along with locating the hole in the inner tube. By doing this, you narrow down the area of the tire you need to investigate.

Puncture repair kits have improved to the point where a good puncture repair can be regarded as permanent, making it worthwhile to fix the tube. To repair a tube, first pump the tube so that is about two inches across. If you're using a track pump, go carefully; it's quite easy to completely destroy a tube by over-inflating it until it explodes. It's not unheard of. To find the hole, pass the inflated tube near to your face and listen for the hiss of escaping air. If this doesn't work, the hole is very small and the way to find it is to carefully inspect the tire by eye.

Eventually you will find the hole by getting a thin jet of air in your eye. This can take some time, though. The foolproof way of hunting for a hole in a tube is by passing it through water, but this has the disadvantage of leaving the tube wet, meaning you will have to let it dry before you fix it. However, it is a useful when you're searching for a tiny pinhole that can cause very slow punctures. Inflate the tube gently to test the seal and leave it for an hour or so, allowing you to tell whether it's deflating. Don't excessively inflate the tube; if you pump the tube above its normal inflated size, you risk blowing off the patch, no matter how good it is.