Presta change-o
June 8, 2009 at 10:30 PM by Dr. Drang
My new bike—which is to say, the bike I’ve had for about three years but which still seems new to me—came with Presta valves on the inner tubes and rims with narrow holes meant for those valves. I’d never had a bike with Presta valves before and didn’t think they’d be much of an improvement, but I decided to stay with them and give them a fair trial. Now I’m done with them. I’ll keep using Prestas until my small supply of spare tubes runs out, but after that I’m back to Schraders.
If you don’t know the difference between the two types of valve—if you don’t even know that there are two types of valve—your bike has Schraders. Presta valves are longer, skinnier, and have a locking stem. The stem—that’s the part in the center of the valve that lets the air out when you push it in—is threaded and a little knurled nut that fits on it can be tightened against the valve body, preventing the stem from moving in and leaking air. Here are two photos1 of a Presta valve, one with the nut turned in to lock the stem,
and one with the nut turned out to unlock the stem,
As you might expect from the different geometry, to inflate a tube with a Presta valve, you need a pump with a connector made for it. Most decent bike pumps have two connectors, one for Schrader and one for Presta, so I didn’t have to go out and buy a new pump when I got my “new” bike.
But I did have to go out and buy a new inner tube pretty quickly. The longer stem on the Presta is easy to bend, and I bent one during one of my first refilling attempts. Because a bent stem won’t fit in the pump’s connector, I had to bend it back straight. This weakened the stem, and it broke off the next time I tried to pump up that tire.
OK, I figured, I have to be more careful with this type of valve. And so I was, and for three years I’ve been gentle when turing the stem locking nut, and I’ve made sure the pump connector was perfectly aligned with the valve before sliding and locking it in place. There have been no more stem failures, although you can tell from the photos above that I haven’t been able to keep the stems from bending a little.
Yesterday morning I had a new type of Presta failure. I was inflating my tires before a ride and was having trouble locking the pump connector onto the rear tire’s valve. My left hand is still a little weak from an accident I had at the end of April—pickup truck vs. bicycle—and I was probably turning and rocking the valve body as I tried to connect and disconnect the pump with my right hand only. As I pulled the connector off the valve, there was a pop and a short hiss of air. The tube wall had torn through at the base of the valve body.
So I’m through with Prestas. They’re just too dainty for me. In their favor, I will say that they seemed to maintain pressure better than Schraders. I refill my tires less often than I refill my wife’s, even though I keep my tires at a higher pressure than hers. Still, I’m tired of the extra care I need to take just to refill my tires.
I will, no doubt, need to ream out the valve holes in the rims2, but I’m not worried about weakening them. This isn’t a highly optimized road bike; a slightly larger diameter hole shouldn’t make the rims crumple.
