Optimal Bike Tire Pressure
Our friend and co-conspirator, the BikeTinker, recently collaborated with some folks to create a tire pressure app for Android devices. I've always felt my understanding of tire pressure remedial: I need fat tires 'cause I'm pushing 225 lbs around...panniers not included. Instead of trying to explain it myself, I thought he could do a better job of summing it up: why is tire pressure so important?
- Harder tires aren’t any faster than softer tires. There’s a sweet spot for tire pressure between too-hard and too-soft, and you waste energy both ways. That sweet spot is a 15% “drop,” which is how much you squish the tires when you get on the bike.
- Front and rear tires need different amounts of air pressure. Bikes put more weight on the rear, which is why rear tires wear faster, and why you have fewer spokes in the front. The rear tire needs higher pressure for the same optimal drop.
- Tire pressure and width should change based on weight and load. Bigger people need bigger tires. Wide tires at the right pressure are as fast or faster than narrow tires. Wider tires are more comfortable than narrow ones.
With math, you can get that 15% drop for every tire, every time. You know what’s good at math? Math Guys. And computers. And now phones. Math does work so we don’t have to, and computers do math so we don’t have to. As an Art guy, I like that. [Here are some ways to get computers to do the math for you]:
There's an Android app!
It’s on Google Play and in the Amazon app store. Amazon lets you try it out in the browser to see if it would be useful. By October 1st, there will be a DEMO version for free. This app exists because I got tired of maintaining the Google Doc spreadsheet I made from the Excel file someone sent me.
There’s a Google Doc.
It’s free. I made it from an Excel file a man named Dave Adams sent to me on the basis of a modified version of Frank Berto’s chart in Bicyle Quarterly, that I had on my blog. A Google update just this week allowed me to lock down the formulas, so it should fire on all cylinders now, and you’ll be spared my impotent rants against vandals.
And, there's the chart that started it all:
It’s vintage. Somehow this made me “the tire pressure guy” to some people, which is funny, because I only air up my tires when they get squirrely. Frank Berto, Jan Heine, Dave Adams, Allan Folz and Scott Tepavich are the Math Guys. I’m just an Art Guy – I drew the bike silhouettes:
Thanks much, Philip!