Editor’s Note: This article is courtesy of the team at Art’s Cyclery. The original post can be found here.
To the uninitiated, mountain biking is a sport full of mystical knowledge, soaked up from the earth via the two-wheeled talisman underneath you. More time spent riding results in more knowledge gained through this intimate connection between rider, machine, and universe.
Unfortunately, the only thing proven to result from extensive contemplation while perched on a bicycle is an ever-growing desire to leave more and more of the “real world” behind as you pedal off toward a new horizon. Real, proven, practical knowledge that results in more enjoyment on the bike is luckily much easier to find, and the ins and outs of tire pressure are an important example.
There’s nothing mysterious about the goal of correct inflation: create maximum ground contact while limiting tire deflection. Too much pressure will prevent the tire from conforming to and absorbing irregularities in the terrain, while too little pressure causes sidewalls to collapse, resulting in tire squirm, a rough ride, loss of control, damaged rims, and possibly the tire coming off the rim. Optimal tire pressure is high enough to maintain shape and traction through turns, but also low enough to conform to obstacles without causing deflection or bottoming out on the rim.
Mountain bike tire pressure is dependent on these variables:
- Rider weight: More weight = more tire pressure.
- Tire volume: More volume, either in width, diameter, or a combination, requires less pressure. “Plus” and “fat” tires represent the extreme of this example, with plus tires requiring less than 15 psi and fat tires able to perform with as little as 4 psi in soft conditions.
- Terrain: Rougher terrain requires less tire pressure… to a point. You need enough bottom-out resistance without creating a harsh, uncontrollable ride. Optimal pressure is where the tire compresses enough to almost touch the rim on the trail’s biggest impacts.
- Rider Skill Level: Faster, more aggressive riders need more tire pressure, since they will be cornering and hitting obstacles with more force, requiring more bottom-out resistance.
- Tire Construction: Lighter, thinner tires require more pressure than thicker, reinforced tires.
- Tubed or Tubeless: Running tires without tubes greatly reduces the chance of pinch flats, allowing for lower pressures in tubeless compared to tubed tires.
Where to start? Here’s a quick guideline to dialing in your mountain bike’s tire pressure. These are not the Commandments of Pressure; if you find that following these numbers leaves your bike feeling too bouncy or too sluggish, then adjust accordingly. The intention is to get you thinking about which direction to run your pressure according to your riding conditions.
For most riders weighing from 160 to 180 pounds, with 2.3″ width tires, riding intermediate terrain, start at 35 psi.
- Drop 5 psi if tubeless
- Run 2-3 psi less in the front tire than in the rear tire
- Add or subtract 1 psi for every 10 pounds you are over or under the stated weight range, without dropping below 25 psi to start
- Add or subtract 2 psi for every tenth of an inch your tires are under or over the stated width
- Write down your starting psi and pay attention to cornering and bottoming out on your next rides
- If you find yourself wallowing in corners, or bottoming your tires out harshly, add 3 psi
- If your bike feels skittish, bouncy, or harsh in rough stuff, subtract 3 psi
- Every time you change your psi, write it down!
Unfortunately—or luckily, depending on how you look at it — finding your perfect tire pressure will take some trail time. However, once you understand how your bike reacts with varying tire pressure over specific terrain, you will be able to eliminate one more variable in your performance equation.
What are your secrets for nailing tire pressure? Let us know in the comments section below.