6 Quick Tips for Mountain Biking on Pumice

Jul 14, 2021

Mammoth Mountain was at the forefront of downhill-mountain biking in the 1980s, thanks to the progressive and creative vision of Mammoth VP, Bill Cockroft. I’d heard so much about the legendary bike park, so when I first moved to Mammoth and had the chance to ride the famed trails I was pumped—but no one told me about the pumice.

My excitement for the trails translated into downhill speed. Riding down Breakthrough, an intermediate trail that descends from McCoy Station and eventually runs into the Downtown Mountain Bike Trail, I learned the hard way about pumice.

Most of us who love the area know that Mammoth Mountain sits on the edge of an active caldera and with the volcanic region comes a host of igneous rock. I never considered this would affect the mountain bike trails, which I thought were just singletrack carved into the dirt, but alas the mountain has a lot of pumice that troubles even the most experienced mountain bikers.

Pumice is a light-colored rock that is extremely porous and formed during volcanic eruptions, which explains why we have so much of it in the region. Because pumice is so lightweight, it’s difficult to navigate on a mountain bike—it’s like riding on sand, but with less resistance.

If you are anything like me on my first day riding on Mammoth Mountain, you’ll be unprepared and learn quickly that the reward of crashing in pumice is at best an uncomfortable raspberry abrasion. (Pumice is the same rock that is used to scrub feet of dead skin and calluses.)

But you don’t have to learn the hard way, like I did.

1. Ride a bike with fatter tires

After a few good crashes I went to a local bike shop, and they recommended I switch out my tires for a wider set. The skinny cross-country tread that I rode in Southern California was not the best choice for Mammoth Mountain.

“Look for a tire that has a wide tread pattern with good cornering knobs,” says Footloose bike shop employee, Kevin Cadotte. “The wider tire will help accommodate looser dirt like sand or pumice.”

Wider tires handle better in pumice and are likely to last longer. When I first put wider tires on my bike, I noticed a substantial weight difference and was slower on the uphill trails, but I quickly got used to the extra weight and it paid off in less downhill wrecks.

2. Lower your seat

It might seem obvious, but a lower seat helps with any downhill riding because it lowers your center of gravity and you are less likely to go over the bars. What’s even better when riding downhill on pumice is to lower your seat and hang your rear far off the back.

“Have your seat low and your belly bottom behind the bottom bracket,” Cadotte says. “Get your weight back and use your back tire as a rudder.”

3. Steer with your Body

Rather than steering with the bars, you will use your weight, shifting side-to-side, and steering from the rear. This is not nearly as difficult as it might sound. Give it a try on an easy trail first just to get the hang of it.

4. Always Look Ahead

You can prepare what’s next if you are constantly looking down the trail to anticipate what’s coming next. Generally in mountain biking you will hit what you look at, so stop looking at that tree or large rock on the side of the trail and focus on where you want to go. Knowing what’s ahead on the trail will help you prepare for loose pumice sections. Get your weight back and be ready to slide.

5. Expect to Slide

By now you know that pumice is loose, so be prepared to slide around a little. If you can resist the temptation to turn the wheel, just let the bike slide and control the motion with your body. “Let your tires drift,” Cadotte says. “Get comfortable letting the bike slide. Just lean the bike and use your body weight.”

6. Take it easy on the brakes

If you are riding fast and heading into a stretch of pumice, the worst thing you can do, which is a natural reaction for most, is to slam on front brakes. The faster you ride through a soft surface the less likely you are to crash. Even worse than braking, is only hitting the front brakes, which will most likely send you over the bars.

Monica Prelle

Monica Prelle is an outdoors, wine, and travel writer who would rather be running, climbing, or mountain biking. See more of Monica's posts here, read more of her work at monicaprelle.com and connect on twitter @monicaprelle

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