For mountain bikes, tire pressure is an integral part of a system of shock and impact absorption. Top-level mountain bikers vary their tire pressure according to terrain, making a good pump an essential part of any mountain biker's kit. Mountain bike pumps come in portable versions and as floor pumps for at-home use, and the best pumps for mountain bikes have key features that make a quick pressure adjustment easier.
Stem Your Enthusiasm
The best pump for you depends on the valve stem on your mountain bike's tubes. Valve stems come in two varieties for bicycles. A Schrader valve is the most common, and is identical in design to the valve on a car tire. This lets you make use of any pump designed for car tires to refill your mountain bike, which can get you out of a jam if your pump breaks on a long bikepacking trip. The second variety is the Presta valve, which leaks air slower than a Schrader valve and is less prone to damage from the rim. The Presta, however, is a specialized valve used only on bike tires, so you'll need the right pump or a screw-on adapter.
Gagueing Your Success
For the best performance from your mountain bike tires, you can adjust the pressure to match the terrain you're on. For loose soil, reducing the pressure a bit below the manufacturer's recommendations can give you better flotation and traction, and for hard-packed trails, you can increase the pressure for a firmer tire with less rolling resistance. A good pump for mountain biking has a built-in gauge so you can check your tire pressure after you fill up, ensuring you've got your pressure right where you need it before you hit the trail. PSI gauges also prevent overfilling or underfilling a tire, which can be dangerous.
Getting Pumped Up
A mountain biker should always have a portable pump and a patch kit on board before going off-roading. Portable pumps use a compact design that usually straps to your frame to remain unobtrusive when not in use. For mountain bikers, it's important to have a solid pump holder that bolts directly to the frame at the bottle cage; losing your pump on the trail could lead to a long walk home. Some portable pumps are designed to accommodate both Schrader and Presta, which can be useful if you need to help out another cyclist who uses a different valve than you do.
Other Pump Varieties
For mountain bikers, owning other styles of air pumps can sometimes make sense. A floor pump is a great addition to your garage or basement workshop, because these pumps are more comfortable to use. This makes it easier to keep a good tire pressure for every ride. Some riders who use Presta valve stems on their mountain bikes swear by CO2 cartridge pumps, which use a small canister of pressurized CO2 to inflate a tire in seconds with no pumping required. These pumps can only be used a small number of times before they're shot, so if you expect to be out for a longer trip, you may want to stay manual.