By Omar Bhimji
The most common type of bicycle tire is known as a clincher, and derives its name from an airtight rubber tube that sits – “clinched” – between the tire and the rim. When a cyclist “gets a flat,” the tube develops a hole, the air escapes, and the tube deflates. Here’s a list and description of all the flats I’ve ever known, and how to avoid and/or repair them.
By far the most common type of flat, a puncture occurs when something sharp pierces the tire and the tube. Usually the culprit pierces the outside of your tire, but the hole can also be caused by a spoke poking the tube from the inside (check your rim tape to make sure it’s still covering the spokes). Depending on the size of the hole, a puncture can cause a tube to deflate slowly, say overnight, or in a matter of seconds. You can avoid punctures by replacing your tires when the tread starts to wear out, not riding over anything sharp (duh), and by keeping your tires well inflated. The higher the air pressure in your tire, the harder the surface it presents to sharp objects and the less likely it is to be pierced. You can fix all but the smallest punctures (which are hard to find) and the largest punctures by patching them. You’ll also want to check your tire after a puncture to find the culprit and any of his buddies who might be lurking in the rubber of your tire, just waiting for the chance to ruin your day.
The Pinch Flat
This type of flat occurs when an inflated tire meets a hard object (like a rock or a curb) with enough speed and force that its tube is pinched between that object and the rim of the bike’s wheel. Pinch flats usually cause large tears in the tube, which deflates instantly and can be difficult to patch. Depending on the size of the hole and your patching skills, a new tube might be your only recourse. Again, you can guard against pinch flats by avoiding slamming your wheels into anything hard and by keeping your tires well inflated – the more air pressure your tires contain, the less likely they are to compress under impact to the point of tearing the tube.
This the only type of flat that results in a “Bang!” Every other type of flat causes a hiss. The only way a tube can be inflated to the required level of pressure is by being encased by the tire and rim. Blowouts usually occur when the tube escapes from the tire. If a tear or hole in the tire is large enough for the tube to pass through, it will pinch against itself and explode.
Another cause of blowouts is a poorly seated tire. If the tube is inflated while part of it is between the bead of the tire and the rim, or if the tire’s bead is malformed or loose, the tube can push the tire off the rim and escape, usually exploding in the process. You can avoid blowouts by making sure that there are no holes in your tires, and that they are properly seated on the rim before inflation. The only remedy to a blown tube is replacement – just hope that the blowout didn’t damage your tire, too.
Whether from a manufacturing defect or abuse of the valve stem, it is possible for the valve to separate from the tube, creating a hole. The good news is that valve failure or tearing almost always happens during tire inflation, not while riding. The bad news is that there’s no way to guard against or repair this kind of flat – your only recourse is a new tube. Valves can also become loose and start leaking air. If you try the water trick below and bubbles seem to be coming from the valve itself, you can have it tightened at any bike shop.
Sometimes, your tire keeps going flat and, in spite of your or a mechanic’s best efforts, no hole can be found. This type of flat is almost certainly the result of a hole (created by a puncture) so small that it can’t be detected – though there’s always a chance that your bike or wheel is haunted by a malevolent spirit. Try holding the tube, inflated, under water and looking for the telltale trail of bubbles. If you still can’t find the hole, replace the tube (again, after checking your tire for the culprit), or call an exorcist.