How to Pump Up Your Tires

Properly inflating a tire is a magical thing – it’s a simple adjustment that can result in a major improvement in your ride. Underinflated tires have excess surface area in contact with the ground, creating more friction to work against – they’re also prone to flats. You can sit on a bike and see underinflation at work: Are your tires splayed out where they meet the ground? Can you squeeze either tire between your fingers with ease? If you’re working really hard to get moving, and your bike’s in otherwise sound shape, chances are that your tires need air.

Step One: Look It Over

To determine how much air to put in your tire, read the PSI (pounds per square inch) recommendation printed on the sidewall. These numbers are based on manufacturer calculations balancing safety and performance.

It’s best to inflate to at least the minimum recommended PSI, but try not to go too much over the max, even though you sometimes can. Different tires have different specs; a good rule of thumb is that your tires should be firm, but not rock-hard.

Now, check the tire to make sure it’s correctly seated on the rim. Make sure that the valve sticks out at right angles to the rim, and that there’s no dry rot (cracking) on the tire sidewalls or excessive wear on the tire surface.

Step Two: Pump It Up

Remove the plastic dust cap from the valve and place it somewhere close by, as these are easily lost. If you have a Presta valve, loosen the knurled nut completely and tap the needle gently inward to make sure it’s not stuck in place (if the tire already has air inside, some will hiss out when you do this). Make sure the fitting for your pump is correct for your valve – the wider aperture is for Schrader, the narrower one is for Presta.

If there’s a locking lever at the pump head, make sure it’s unlocked. Slide the pump head onto the valve. Once the pump is firmly attached, secure the locking lever to fix the head in place. Start pumping, checking the pressure as you go until you reach the recommended PSI. Unlock the lever and quickly remove the pump head. If you have a Presta valve, re-tighten the knurled nut. Replace the dust cap, and you’re done!

What’s Your Valve? Schrader vs. Presta

Inner tube valves in North America mainly come in two varieties: Schrader or Presta. Schrader valves are fatter, with a spring-loaded pin and a plastic dust cap. They’re common on less expensive bikes, older bikes, mountain bikes and utility bikes. (They’re also found on car tires.)

Presta valves are narrower and springless, with a knurled nut on the valve needle that acts as a built-in valve cap. Appearing mainly on high-performance bikes, Presta valves hold higher air pressure than Schraders, and often include a useful lock nut at the valve base to hold the valve steady at the wheel rim.

Each valve type requires its own pump fitting, but most bike pumps come with a dual or reversible fitting that adjusts to fit either valve. Only Schrader valve inner tubes can be pumped up with gas station pumps, but you can buy an inexpensive screw-on brass adapter for Presta tubes that allows you to use Schrader-fitted pumps.

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).