Grimy Handshake: Geometry Lessons

Change, it is often said, does not happen in a vacuum. One shift in thinking can lead to a concurrent reaction in behavior, which can lead to a domino-fall of consequence that eventually can reshape the way we all act and think. Cause and effect, action and reaction, ripple outward and create more cause and effect, more action and reaction. Whether we are talking about species evolution, politics or bike design, this holds true.

A few years ago, I opined that the pendulum of mountain bike geometry was swinging past one of my favorite navigation points—the Schwinn Excelsior DX—back in the direction of slacker head angles after a couple decades catering to a decidedly steeper, cross-country-race-friendly emphasis. I also speculated that we were reaching the end of the pendulum’s swing, as the head angles and reach numbers on general-duty trail bikes were getting into what had been the sole domain of downhill bikes not too many years prior. The thick part of the mountain-bike-buying bell curve, I assumed, would balk at these new plows. Turns out I was wrong (yet again, just like when I said elastomers would be the future of suspension …), and the pendulum has continued to swing out into the long-and-slack frontier. How? Why?

The evolution of bike geometry is an ongoing and collaborative/competitive experiment. Manufacturers are looking to sell bikes. In order to do that, they need to sell bikes that people want to buy. The first mountain bikes were modeled after old Schwinn cruisers because that was as sensible a starting point as any. For a time, XC riding and racing was seen as the dominant market, and so bike design moved from heavy and slack toward light and steep, head angles ratcheted up, and nobody seemed to mind wearing Lycra. Then, Canada, freeride, yada yada yada, and large numbers of mountain bikers began thinking that this was more fun. Cue widespread carnage defined clearly in broken helmets, collarbones and bike frames. Steep, twitchy bikes climb tight, nadgery trails well, and they are rockets going up fire roads, but they pretty much suck everywhere else. So, head angles got slacker, wheelbases got longer, tires got wider, wheel diameters expanded and here we are. But there are some nuanced points along the way to consider.

One of the prime indicators of the coming change, if you were to look back a decade-and-a-half, would be the return of the rise bar. Not only did riser bars come back, they got wider. And wider, and wider again. Hand in hand with that, by necessity, stems got shorter and shorter. Narrow bars and long stems work pretty well together, but wide bars and long stems, not so much. It creates an odd tiller effect at the front of a bike. Likewise, narrow bars and short stems are grim. A short stem needs some more bar width to influence a front wheel to turn. Meanwhile, slacker head angles were being met with greater fork offset. This was seen as a way to keep trail (a measurement derived from the fork offset and the head angle, and wheel size, as measured along the ground by dropping a line down vertically from the front axle and measuring the distance that it ‘trails’ behind a line extrapolated out from the center of the steering axis) in a generally recognized sweet spot. This was thought of as one of the cornerstones of predictable bike handling.

However, as reach numbers grew, and stems got shorter (longer toptubes and short stems also go together like peanut butter and bananas), head angles slackened, and seat angles steepened (finally, hallelujah!), wheelbases got longer and longer, and the big lump of meat on top of the bike found it more difficult to get enough weight over the front wheel at speed. Hence the most recent geometric evolutionary twist being explored by a certain scrappy brand out of Bellingham—reducing rake to bring the front back ever so slightly beneath the rider in order to maintain traction on the front and enhance stability.

Meanwhile, how we ride has continued to change. Modern suspension is great, and bikes really do climb pretty damn well (especially when you consider how long and slack they are, and how antithetical that is to the road-derived traditional paradigm of what constitutes ‘good’ climbing). But don’t fool yourself, from a majority perspective, mountain biking is really not defined by climbing anymore. Trails are now built for mountain biking; switchbacks are disappearing in favor of sweeper berms, shuttles are a common part of the vocabulary and the chunky, hike-a-bike groveling of the ’80s and ’90s is the stuff of sepia-tinted memories. People are riding trails built for slacker, longer bikes, and they are riding them faster. As such, wheelbases in excess of 47 inches are now seen as an advantage, not an impediment, for most riders in most terrain. Whether or not we want to admit that we are actively a part of this changing landscape, the landscape is changing.

Is there a downside to the current evolution? Absolutely. If you favor really tight, techy, old school trails, new school bikes handle well but are loooong, and they are a pain in the ass to muscle between narrowly spaced trees and around switchbacks that would have been tough to clean with a 42-inch wheelbase. And those old-school trails themselves are changing. In heavily populated areas, apexes are getting wider, corners are getting blown outward and tight lines are disappearing entirely. Whether ancient trails hacked into the earth centuries before mountain bikes came along are experientially better or worse than carefully radiused berms and rolling dips that serve double duty as erosion control and jump face is like arguing whether electricity is better or worse than fire. Context plays a big role.

For my part, I have no sentimental urge whatsoever to ride the bikes I was riding in the 1980s, but I sure do miss some of those trails.