Types of Pump
Floor pumps (large, solid, sturdy upright standing pumps with a built-in pressure gauge) and mini pumps (small and portable) usually come with Schrader and Presta valve settings. The third variety, the gas station pump, fits only Schrader valves. Use caution when inflating at a gas station: those powerful air compressors can quickly cause dangerous blowouts. Make sure the tire is properly seated on the rim, then proceed incrementally, using a pressure gauge to check your progress.
How Much Air?
Pumping tires to their optimal pressure is pretty straightforward, but it helps to have a little knowledge about how tires and inner tubes work. Your bike's tire is kept inflated by a rubber inner tube situated snugly inside the tire, nestled in the rim. The inner tube valve protrudes from the rim at right angles to the rim surface, through a drilled hole set between two spoke holes.
If overinflated, your tire may lose traction, blow off the rim or burst. And an underinflated tire is more vulnerable to pinch flats (called "snake bites" due to the two distinctive holes that it produces in an inner tube). Without enough air, a Schrader-valve tube can also slide around inside the tire until the valve stem moves to the side and eventually tears at the valve stem base – a hole that's difficult (if not impossible) to patch.
To see if you've gotten the pressure right, sit on your bike and check the tires. At optimal inflation, they should bulge out just a teeny tiny bit where they make contact with the ground. No bulge means they're probably overinflated; too much bulge means you can put more air in there.
Tip
Align your inner tube valve with the tire pressure information on your tire. That way you'll have the maximum and minimum tire pressure in plain view the next time you go to inflate your tire.
The late Sheldon Brown's website has a great in-depth rundown of the physics of tire inflation: sheldonbrown.com/tires.html
Anne Mathews lives in Seattle, where she rides bikes, fixes bikes and plays music with the Toy Boats (thetoyboats.com), the Lonely Coast (thelonelycoast.com) and Orkestar Zirkonium (orkestarzirkonium.com).
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