There are two types of valves common to bicycle tubes, Presta and Schrader.
Schrader valves (SV), also called American-type valves, are common on kid’s bikes, beach cruisers, most hybrids, and many recreational level mountain bikes (as opposed to more performance oriented models). It’s the same valve that’s used on car tires, and they work with most pump and compressor heads without any special attachments. The plastic caps aren’t necessary to hold air in, but do keep dirt from accumulating. It’s a good idea to replace them if lost or broken.
This is a closed Presta valve (PV), AKA French-type valve stem, common to road bikes and many nicer mountain bikes. We get lots of questions about the how and why of Presta valves. Here’s why: Presta valves are better at holding higher pressures because you physically close the valve after inflation rather than depending on a tiny spring to hold the air in. Road bike tires regularly have recommended pressures of 120+ psi. Also, because you don’t have to overcome a spring, it’s easier to operate the pump as you approach higher pressures (than a Schrader valve, which get difficult at higher pressures because of the pressure pushing against the spring on the inside of the valve). Further, because the stem of the PV is thinner, a smaller hole can be drilled through the rim, which is more structurally sound than the larger hole of the SV. This doesn’t really matter if you’ve got a wide rim (like many hybrids and cruisers), but can matter a lot with the narrower, deeper V rims on road bikes. Valve caps are completely unnecessary for Presta valves, so when you lose one, don’t worry about it. None of us use them on our own bikes.
Here’s the how:
All you really need to pump up your PV equipped tires is a decent pump (read: from a bike shop, not a big box store).
First, open the valve by twisting the top to the left (righty tighty, lefty loosey). It will stop when it’s fully open, so keep twisting until it stops.
Tap the valve to clear it; if there’s any pressure behind it (i.e. it’s not a brand new un-inflated tube), you should hear the “psh” sound of air escaping.
Install your pump on and lock it down onto the valve stem (this varies by pump brand). Inflate to recommended pressure. When you’re there, unlock the pump head and pull it off the valve stem. Try not to twist it off or yank it; gently pull straight back, away from the stem.
Close the valve by turning the top to the right to tighten. Twist until it stops.
That’s it. Pretty simple if you have the right tools. So what if you have a cheap pump or a compressor that’s not compatible? There’s a simple fix: the PV adapter.
1. Open the PV
2. Screw down the adapter (O-ring side down)
3. Inflate as you would a SV
4. Remove adapter
5. Close valve
PV adapters work fine, and are cheap (about $2), but require the extra steps of installing and removing, and are notoriously easy to lose (we recommend storing them on the valve stem by screwing them on upside down). Sometimes people try to outsmart the system by leaving the PV open and the adapter installed all the time. This is a bad plan because the vibrations and jolts caused by bumps/curbs/cracks/roots/potholes/etc. will let out little bursts of air and you’ll be flat before you know it, and you won’t know if you’re flat because the valve is open or if you’ve got something stuck in your tire. Best bet is to invest ($30-$45) in a decent bike shop quality pump that will work with both valve types without any special adapters, and carry a PVA around in your bag as a back-up plan.
One final note: it’s generally recommended that you stick with the type of valve that the rim is drilled for. The skinnier PV will fit through the larger hole intended for SV’s, but due to the extra space can wiggle around and eventually get cut on the sharp inner edge of the hole. There’s a rubber grommet that fits into the hole that basically works like a shim so that the stem doesn’t move. This works, but is less than ideal. Similarly, it’s possible to drill the smaller PV hole out to fit a SV, but this could weaken a narrower rim. Think for a moment about the pressures you’re exerting on your wheels and ask yourself if you really want to potentially compromise wheel strength.
Let us know if you have any questions, and feel free to leave feedback or add your own experiences. Cheers!