I headed off from my house one Saturday early in my biking career, drooling with excitement for the mountain bike ride I’d been awaiting all week. Then, before I had reached the trailhead, I noticed my rear tire was significantly low. I felt like I was riding through mud – on the pavement! Remembering a gas station with an air pump on my way to the trailhead, I figured I could easily pump up my tire without a wasted trip back to my house.
But, when I tried to inflate my mountain bike tire… AAACK! Foiled! The gas station had a standard car pump and, new biker that I was, I forgot my bike tires have a presta valve. A week of hungering for a mountain bike ride… RUINED! All because of a puny little valve. Oh, the angst. Do NOT let this happen to YOU!
What is a Presta Valve? Are Presta Valves Common on Mountain Bike Tires?
Unless you grew up biking, most of us are so familiar with car tire valves, we assume it’s the only type of valve. In truth, car tires use what’s called a Schrader valve. It’s about the diameter of a pencil and has a tiny “button” in the center that, when pressed, allows air in or out, but holds air pressure relatively steady when not compressed.
Presta valves, on the other hand, are significantly skinnier than Schrader valves. They don’t have a button in the center of the valve and instead have an attached screw mechanism at the tip. When screwed closed, it holds air pressure in the tire. When unscrewed, you can pump air in or release air out.
Currently, presta valves are the most common type of valve on high-end mountain bikes. Racers and high performance cyclists prefer them. They’re becoming increasingly common – even on mountain bikes on the low-end of the price spectrum.
Why, you ask. (Perhaps with a significant number of swear words as you kick your flat mountain bike tire or throw your useless Schrader pump.) Why use an uncommon, obscure valve that doesn’t fit a standard pump? Is it just to make mountain bike newbies suffer? Why? Why?
Benefits of Presta Valves:
No, it’s not just to frustrate you.
Presta valves are generally more reliable and allow pumping your tires to a more precise pressure. By virtue of design, all Schrader valves release tiny amounts of air over time, requiring occasional “topping off”. Having a cap on the valve can significantly decrease the air loss, but it still means, at any given moment, your tire may not have the pressure you pumped it to.
A casual mountain bike rider may not know what pressure they should be riding or even notice when the pressure is off. But for high-speed riders, tire pressure can have a significant impact on speed, race performance and riding safety.
The screw on the tip of the presta valve allows a rider to close off the tube at the desired pressure and not require a cap. Barring an unnoticed leak or a puncture during a ride, the tire will now reliably hold the pressure you want.
How Do You Inflate a Presta Valve with a Common Air Pump (Gas Station)?
You can inflate a presta valve with a common air pump, such as at a gas station or portable air compressor. However, you need an adaptor that’s ridiculously small in size but huge in importance: a presta valve adaptor.
Here are the steps to inflate a presta valve with a standard pump:
- Unscrew the screw on the tip of the presta valve.
- Place the valve adaptor on the tip of the valve.
- Engage the pump to inflate your mountain bike tire to your chosen pressure.
- Remove the adaptor and screw the presta valve closed.
Since more and more mountain bike tires use presta valves, most bike pumps are either universal (meaning one hole works on both presta and Schrader valves) or they have two separate holes, one for each valve type. However, you should always carry a valve adaptor when you ride for situations when a standard pump is the only option. Some cyclists do this by keeping a valve adaptor screwed on their tire valve all the time. Just make sure the valve is screwed closed before putting the adapter on!
Where Can I Get a Presta Valve Adapter?
Presta valve adapters are extremely tiny and portable. This also means they’re easy to lose. The good news is they’re fairly cheap. I usually buy a handful at a time and keep one in my garage bike tools and one in my portable tool kit for rides. Having one in your glove box isn’t a bad idea, either!
All bike shops sell valve adapters and some general sporting goods shops and hardware stores carry them as well. You can also buy valve adapters online easily and cheaply.
What Pressure Should You Inflate Your Mountain Bike Tire?
This simple question actually does not have a straightforward answer. The simple rule is to refer to the tire manufacturer’s specs on tire pressure that are printed on the sidewall of your tires. Consensus of riders is that mountain bike pressure should be 30 psi on the front tire and 33 psi for the rear tire. This information should serve you well if you have only a casual interest in mountain biking and are doing entry-level to intermediate trails two or three times a month.
However, if you spend a significant amount of time on your bike (and an equally significant amount of time dealing with pinch flats, blowouts or skidding out on corners), you’ll want to dive deeper into the science of bike tire pressure. DIY Mountain Bike has a fabulous, in-depth article and survey results examining appropriate bike tire pressure.
How Do You Check the Pressure of Your Mountain Bike Tire?
The fastest and easiest (and cheapest) way to check your tire is with your hand. When you squeeze it, it should be hard in the center with only a tiny bit of give farther out on the tire near the treads. A hand test, however, is – not surprisingly – not very accurate!
If you want to be precise, a tire pressure gauge will be necessary. But be warned: tire pressure gauges are notoriously unreliable and the sensitive sensors are easily broken. For my recommendation, read my tire pressure gauge product review.
How Do You Inflate a Presta Valve without an Adapter?
If you’re in a pinch (perhaps literally!), and you don’t have a universal pump or a valve adapter, you can modify a tube cap to create a functional adapter using a presta valve CAP.
- Remove the valve cap. Find the place on the valve cap where it gets smaller. Cut at that spot with scissors or whatever you have that will do the trick. Throw the tiny tip away.
- Unscrew the valve on the tire.
- Place the modified cap upside down on the tire and screw it down a few twists.
- Attach the pump and inflate.
Remember to screw the tire valve shut after inflating! I know you’re tired of hearing that, but it’s important.
Now that you know everything you need to about how to inflate a presta mountain bike tire, you’ll never find yourself hungering for a ride and find yourself deterred by a standard tire pump!
And don’t forget to screw the presta valve closed…
Professional writer Kat Jahnigen was 2 miles from the nearest village – and roughly 2,310 miles – from the nearest English-speaking town – when her bike tire burst. At that time, she was a college student on a bike trip across the desolate, rocky island of Crete. It suddenly occurred to her that it would’ve been good to learn some basic bike repairs before setting off on a solo bike trip.
Check out Kat’s website WriteHire at writehire.net.