In 2006, Krista Rust left her job as an Electrical Engineer for Motorola to race her bike, and she's been traveling, riding, and helping people keep their bikes rolling ever since. Krista is an ambassador for the benefits of tubeless and has spent years helping riders make the switch from inner tubes. Originally an XC racer and now on the enduro scene, Krista lives a life on the road traveling and racing around the world. We've asked her to weigh in on some of the most common questions people ask about tubeless performance. In Part 1 and Part 2 of our series of articles about tire pressure, Krista taught us about too low and too high tire pressure. In this Part 3, she explained how some other key tire properties affect our choice of tire pressure and influence our riding experience. In Part 4, she reveals her tried and tested method of finding the perfect tire pressure.
My method is to simulate a sharp edge rim strike before heading out for a ride, by hand. I lay the thumb of one hand across the tire, perpendicular to the rim. Pressing with the palm of the other hand, I put all my body weight into a hard/fast “strike”, where my thumb acts as a square edge. This gives me a feel for how closely a square edge impact will come to the rim. If I feel like the “strike” allows the tire to collapse too easily, then I’ll add air. Note that it’s important to press with the thumb only and not the entire palm because using the palm spreads the force out too much and doesn’t simulate an edge impact. Another way to figure out optimal tire pressure is to ride and get actual trail feedback. If you are dinging the rim, add air. If you’re not dinging the rim and are bouncing off rocks too much remove air (assuming your suspension is dialed in correctly). If you feel the tire get squirrely in an aggressive turn, adding air may help. Whatever your methodology, once you find the ideal pressure for a specific tire/rim, take measurements for both front and rear tire with a pocket size air gauge, and then carry and use this same gauge when trying to replicate your pressure later. Front vs. Back Tires
It’s typical for riders to run a little less pressure in the front than in the rear when using the same tire make and model on both wheels. For me, this exact difference is primarily based on what it takes to prevent dinging the rims. As an example, given my weight, riding style and tire selection, the 2.3 WTB Vigilante Tough (DH casing) High Grip (sticky rubber) is supportive enough to not fold over in turns, provide some drift and not feel too bouncy in rocks when I ride with 18-19 psi in the front and it at 20-21 psi in the rear, with both mounted to either Stan’s NoTubes Bravo or Arch rims. However, I usually run 22/24 psi (front/rear) with Maxxis tires. Keep in mind that these numbers are according to MY gauges, which could differ substantially from anyone else’s. Which is exactly why you should always double check your tire pressure by feel after you pump them up according to your gage’s pressure. Fine Tuning
More tire pressure gives a quicker bite in loose-over-hardpack conditions, but may result in skipping. However, less tire pressure can provide a more supple drift in loose-over-hard pack corners. In general, a quicker bite is more beneficial in tacky conditions, when the tire will hook up better. Pressure is not the only factor, though. Knowing if a side knob is stiff enough to hold up in a corner is also part of the equation, and it, too, varies with rider weight and/or riding style. All Photos by Kenny Wehn.