Presta vs Schrader valves

The quick answer

Nearly every bicycle tyre in South Africa uses one of two valves. A Presta valve is thin, tall and finished with a small brass lock nut you unscrew before pumping. A Schrader valve is wider, blunter and identical to the valve on your car tyre. If you can push a pin down inside the valve with your fingernail, it is a Schrader. If there is a tiny nut on the tip that needs unscrewing first, it is a Presta.

Presta valves

Presta valves — sometimes called French valves — were designed for narrow rims and high pressures. Because the valve body is slimmer, the hole drilled into the rim can be smaller, which leaves more material in the rim and keeps it stronger. That is why you find Presta on most road bikes, gravel bikes and the better mountain bike wheelsets.

The lock nut at the tip is part of the seal. With the nut screwed closed, air cannot escape. Unscrew it a few turns, press it briefly to release a puff of air, and the valve is open for business. Many Presta valves also have a knurled ring at the base that holds the valve steady against the rim while you attach the pump head.

• Slim stem, roughly 6mm across.
• Threaded body on many models, with a lock ring at the rim.
• Small lock nut at the tip that must be opened before inflating.
• Common on road, gravel and higher-end mountain bikes.

Schrader valves

Schrader valves are the wider, car-style valves you will find on commuter bikes, kids' bikes, older mountain bikes and most budget wheelsets. Inside the stem sits a spring-loaded pin. Push the pin and air moves; let go and the spring seals it again. Nothing to unscrew, nothing to remember.

The trade-off is size. A Schrader valve needs a wider hole in the rim, and the spring means the valve needs a little more pressure before it opens. On a hand pump you feel that as extra resistance in the first few strokes. On an electric pump you will not notice it at all.

• Wider stem, roughly 8mm across.
• Spring-loaded pin visible inside the opening.
• Usually protected by a screw-on plastic dust cap.
• Common on commuters, kids' bikes and many mountain bikes.

How to inflate each one

For a Presta valve, remove the dust cap, unscrew the lock nut all the way until it stops, tap it once to check air moves, then push the pump head on straight and square. Lock the pump head if it has a lever. Inflate to your target pressure, remove the head briskly, screw the lock nut closed and replace the dust cap. That last step matters: an open lock nut will leak slowly over a week.

For a Schrader valve, remove the dust cap, push the pump head on until it seats, inflate and pull the head off. There is no lock nut and nothing to close afterwards. Just put the dust cap back so grit stays out of the pin.

Whichever valve you have, support the valve stem with your free hand while you attach and remove the pump. Levering a pump head sideways is the most common way people tear a valve off an inner tube.

Adaptors, rims and common mistakes

A cheap brass Presta-to-Schrader adaptor screws onto an open Presta valve and lets you use a petrol-station air line. Keep one in your saddle bag — it weighs nothing. What you cannot do is fit a Schrader tube into a rim drilled for Presta: the hole is too small. The other way round works, but the tube will rattle in the oversized hole unless you fit a rim grommet.

Two mistakes cost people the most tubes. The first is forgetting to open the Presta lock nut, then pumping hard against a closed valve and blaming the pump. The second is inflating a tube that is pinched between the tyre bead and the rim, which blows out with a bang. Before you add pressure, squeeze the tyre and check that the bead sits evenly all the way round.

Petrol-station air lines deserve their own warning. They deliver a huge volume very quickly and their gauges are often wildly out. If you use one, add air in short bursts and check the pressure with your own gauge.

Which pump fits which valve

Most decent pumps handle both valves, either with a reversible head or with a dual-opening nozzle. The Freewheel Pocket Pump fits Presta and Schrader, shows the pressure on a digital PSI gauge, and shuts off automatically at the pressure you set. It is rated to a maximum of 150 PSI by the manufacturer, so it has headroom above everyday tyre pressures.

Not sure what pressure you should be running once the pump is attached? Read the bike tyre pressure guide next, and always check the numbers printed on your tyre sidewall first.