Six Rules for Tire Pressure Selection

“What size tires you riding?”

“42, but mounted on a wide internal rim, and I’m running them pretty soft.”

“Nice, what pressure?”

So goes the classic pre-gravel ride bull-session, online forum debate and countless shop discussions occurring across the country this very second. As mixed-surface riding has exploded around the world, equipment is quickly evolving to address the discipline. But with rim and tire size, internal rim width, rider and bike weight, road surface and tire design all adding complex variables to the equation it can feel overwhelming. Here are 6 rules to follow to get you off to the right start, no matter your ride.

1. What goes up must come down: When tire size increases, pressure must decrease. Check out your wheel’s suggestions for pressure based on tire size and start from there, and don’t apply universal rules of pressure across various tire sizes. Just because you used 100psi in a 25mm tire doesn’t mean you should run that pressure in wider sizes.
2. Wheels are boss: Recommended pressure should come from the rim, not from the side of your tire.  While you should never exceed the max pressure written on your tire’s sidewalls, this is a maximum, not a suggestion. If the max pressure recommended by the rim manufacturer is smaller than that of the tire, base your pressure on the rim. Or, better yet, follow the points that follow to dial in the pressure that suits your specific needs. 
3. Max pressure doesn’t mean much anyway: Tire maximum pressures are based solely on blow-off. The fact that a tire “can” inflate to 90 PSI, just means it’s been tested to do so without blowing off the rim. It says nothing about ride quality, rim stress, longevity, wear-patterns or performance. Most tires and rims will roll faster and smoother, handle better and last longer if you run them somewhere in the middle of the recommended pressure range of that rim. Almost no tire will be at its best at maximum inflation.
4. Pressures are unique to riders. Aside from never going below minimum pressure recommendations, your pressure should be decided based on total bike plus rider weight and the terrain covered.  After all, a major part of a “min” pressure is to keep your rim from hitting the ground. If you’re light, running high volume tires, riding on smooth surfaces or making other decisions which limit the risk of bottoming your tire out, you’re free to run lower pressure. If you’re heavy, riding a loaded bike, riding rough, rocky terrain, riding narrow tires, know that you’ve got a habit of taking rough lines or otherwise “hulk-smashing” into obstacles, higher pressure is prudent. In essence, lower pressures put the rim at greater risk of impact damage, but create a better riding bike. Another way to know you’re running too little pressure is your ride feels “squirmy” when cornering or it feels as though your tires are trying to fold over. No one wants that, so air up a touch. The art of choosing tire pressure is about balancing all these forces. 
5. Hooked or Hookless: Whether or not you’re running a “hooked” or “hookless” rim has a huge impact on what pressure you can run. While many modern dirt tires (and a few road) have eliminated side-wall hooks, this reduces the range of tires they can run and pressures which will hold. Generally speaking, “hookless” rims should be matched with wider tires and lower pressures. It’s imperative to follow these wheels’ guidelines as blow-off pressures are lower, and more likely with hookless rims.
6. Lower pressures are faster. Common knowledge used to be that a 19mm tire at 170psi was the epitome of fast.  Since then, studies have shown that with today’s modern tires and wider rims, lower pressure and wider tires create greater efficiency. You can roll faster at lower pressures, while also enjoying a more comfortable, better handling bike.

Most riders have come around to riding bigger tires, but many still over-fill them out of habit. Instead, take a moment to look at your rim and tire maker’s guidelines, consider your application and choose the best pressure for your needs. A better ride will be your reward.