Fixing a Puncture Properly, Including the Step Everyone Skips

What follows is an argument about puncture repair, and about where the received version of it stops being true.

Reading the hole

A single small hole on the outer face of the tube points to something that came through the tread, usually glass, flint or wire. Two small holes side by side on the rim side indicate a pinch flat, where the tube was crushed between rim and an edge. A hole at the base of the valve usually means the tube has been moving inside the tyre or the valve was stressed by a pump.

A long slit or a hole on the inner face suggests a problem at the rim, such as a broken spoke end or a displaced rim tape. Each of those tells you a different thing to fix, which is why finding the hole matters more than patching it.

Finding what caused it

Note where the tube sat relative to the tyre before removing it, using the valve position as a reference point. That lets you translate the hole's position on the tube into a specific section of the tyre to inspect.

By the second week of riding, run a finger carefully around the inside of the tyre, or better a rag, since a rag catches on sharp fragments that a fingertip may not find safely. Look at the outside of the tread in the same area, because a piece of glass often remains embedded and invisible from inside. Skipping this step is the single most common reason a repair fails immediately.

Checking the rim side

Rim tape covers the spoke holes, and if it has shifted or split the tube can be pushed into a hole and punctured. Check that the tape is centred and intact all the way round, and replace it if it is cracked or has hardened.

Feel for spoke ends protruding past the nipples, which happens after a wheel has been rebuilt or spokes replaced. Look at the rim edges for burrs or damage from a previous impact, which can slice a tube under pressure. On tubeless-ready rims, an ill-fitting valve or old sealant residue can also cause repeated mysterious flats.

Fitting the tube without pinching it

Inflate the new tube just enough to give it shape, which stops it twisting or folding inside the tyre. Fit the valve first, then work the tube in all the way round before starting to seat the second tyre bead. Seat the last section of bead with your thumbs if at all possible, since tyre levers at that stage are the classic way to pinch a new tube.

Before inflating fully, push the tyre sideways all round to check that no tube is visible between bead and rim.

Inflate slowly and check that the moulded line on the tyre sidewall sits evenly above the rim on both sides.

Patching versus replacing

At the roadside, fitting a spare tube is faster and more reliable, and the punctured one can be patched at home in comfort. A properly applied vulcanising patch is a permanent repair, and a patched tube is not weaker in normal use.

With a loaded rack, clean and abrade the area, apply a thin even layer of cement, let it dry until tacky rather than wet, then press the patch firmly. Most failed patches come from applying the patch while the cement is still wet or from not roughening the surface. Self-adhesive patches work as a temporary measure and are less reliable over time than the vulcanising kind.

Frames, sizes and riding positions vary enormously; borrow before you buy wherever you can.

Reducing how often it happens

Correct pressure prevents pinch flats, which are entirely a consequence of running too soft for the load and the surface. Tyres with a puncture protection belt genuinely reduce tread punctures, at some cost in weight and rolling resistance. Replacing a tyre whose tread is worn through to the casing removes a very common source of repeat punctures.

Riding away from the gutter avoids the strip where glass and debris accumulate. Picking glass out of the tread occasionally, before it works through, prevents flats that have not happened yet.

The takeaway

Find the cause, check the rim tape, seat the bead by hand — then worry about the tube.

The bike you ride daily beats the better bike you keep indoors.