A few winters back, a buddy of mine did a lot of backcountry skiing. So much skiing, in fact, that he was convinced he’d discovered a new law of physics: "The faster you go," he told me, "the farther apart the trees become." This is your brain. This is your brain on skis.

"There’s a corollary," I responded. "The faster you go, the harder the trees become. Perhaps it’s time to invest in a helmet."

Maybe I’m also influenced by "outdoorphins," as another friend calls them, but I’ve come up with a theory of my own: The faster you go — whether on skis, foot or mountain bike — the smaller a place becomes.

Take the time to walk through the wilderness, and it will feel endless. Trade your heavy pack and boots for a water bottle and a pair of running shoes, and the ground starts to fly away under your feet; the place doesn’t seem as vast as it did. Jump on a mountain bike, and the world becomes smaller still. And it shrinks not just for you, but also for the folks you share it with: They’re privy to your echoing hoots of joy; they have to be ready to jump off the trail when you come hurtling past. Gleeful and courteous though you might be, it takes you just an hour to race over ground they might give an entire day to exploring, and that knowledge somehow changes the shape of the experience.

I’m a trail runner and a cross-country skier, and I’ve been riding mountain bikes since I was a high school kid in the 1980s. I understand the magic of motion, the rush you get from speed.

But all these experiences have led me to conclude that there have to be some limits. When we travel in wilderness areas, I think we should leave our mountain bikes behind. For me, the issue isn’t about the definition of "mechanized transport," or other legal hairsplitting regarding the 1964 Wilderness Act. I just believe that, in a world where wildlands are shrinking daily and it’s tougher all the time to find real solitude, there ought to be a few places that we consent to move through slowly — places that we allow to stay as big, and quiet, as they once were.

The International Mountain Bicycling Association (IMBA) has wisely refrained from fighting for bike access to existing wilderness areas. Nonetheless, many of its members, and even staffers, believe that they should be able to ride in wilderness. And IMBA continues to thrust itself into negotiations over protecting new wilderness areas, insisting that bikes aren’t shut out of trails.

Not everyone at IMBA thinks these battles are worth the trouble. Tom Ward, the group’s California representative, would rather IMBA used its energy to fight for areas mountain bikers really want, instead of reacting to every wilderness bill that comes along. "Why the hell am I arguing for this postage stamp when I’ve got the rest for people to ride?" he asks.

It’s a good question. Why further complicate wilderness legislation, which is already increasingly encumbered with concessions for developers, off-road vehicle riders, oil and gas drillers? IMBA should stay out of wilderness politics, unless it wants to selflessly support protection. And we mountain bikers should be content to leave our bikes behind and travel slowly when we’re out there in what little big country can still be found in the West.