Under Pressure
And so it was that we found ourselves wielding pumps and fancy-pants digital pressure gauges in the freezing cold pre-Iceman parking lot when our neighbor, a guy approximately my age on a very nice, very expensive bike with good tires, joined in the conversation. “I run mine about 50,” he said. “Or I’ll just put ’em right in the middle of the numbers on the tire, so that if it says 30-70, I put in 50.”
Wow.
When customers come into the shop to talk about mountain bikes, we discuss many things: geometry, forks, drivetrain, brakes, but I fear that we very rarely talk about tire pressure, and shame on us for not doing so. You are absolutely not getting the most out of your mountain bike if you’re not dialing in your tire pressure.
In general, there’s been a gentle movement toward lower tire pressure. Lower pressure allows the tire to deform and track over small imperfections in the trail. Conversely, the same tire with higher pressure will tend to bounce over these same small bumps. While higher pressure might feel faster — all loose and bouncy and really hell-yeah-we-are-getting-it-on — the opposite is generally true. The lower limit on trie pressure is controlled by three things: pinch flats, dented rims and personal preference.
Pinch flats occur when the tire is pressed hard against the rim, cutting the tube. Dented rims are obviously a more severe and expensive outcome of the same situation, not enough air to keep the tire off the rim. If you’re running tubes, a dented rim will almost surely have a pinch-flat component. Should you suffer from either, raise your pressure a few psi. (Through interesting decision making (read: tubeless cyclocross setup), I’ve been put in a position in which I need to monitor tire pressure closely. In doing so, I’ve noticed that pumps can vary W I D E L Y in reported pressure. Thus I’d recommend using the same pump or, if you travel with friends or consistently mooch a pump, you might want to purchase a small gauge.)
Personal preference can take many forms. Some folks get a queasy feeling when they bottom out. Personally, I don’t like to “feel flat,” that bouncy feeling you get, particularly from the rear tire, when the air is going out but before it’s riding on the rim. Regardless, you won’t know what you personally like and don’t like without a bit of experimentation.
Where should you start on your pressure journey? Well, that’s tricky, and it depends on a few things: how much you weigh, the size of your tire and wether you’re using tubes or a tubeless system. Here’s good data from Mountain Bike Action, Stan’s No-Tubes and Schwalbe. Remember: all of these are starting points. If you’re serious about this stuff (and, by the way, it is 100% totally cool if you’re not. I get that just a nice ride through the woods is its own reward. But if you do want to nerd out…) you’ll need to do some testing. Maybe even (gasp!) make notes. Regardless, the number is probably less than 50.
