April 01, 2022 3 min read
Originally posted Sep 01, 2018
It could have happened on virtually any bike on the slopes of Kicking Horse, British Columbia on July 1, 2010. I don’t blame the particular brand or model of bike I was riding, but the non-drive-side chainstay broke just behind the clevis, setting up a wobble on a landing that put me over the bars and left me in the dirt. I had to be carted off the mountain, semi-conscious, with a broken collarbone and a concussion.
During the many weeks of healing that followed, I was left to wonder exactly what had happened. My riding buddy had just missed seeing the crash, and my memory of how it happened remains a jumble of random images to this day.
Nevertheless, the crash got me thinking. I had spent decades designing and customizing two and four-wheeled vehicles, most recently as part of the design and development team for the Motoczysz E1pc racing motorcycle. I knew there were lessons from vehicle design that could bring additional stability and more precise control to mountain bikes.
Telescoping forks are amazingly well-developed nowadays, especially considering how simple they are in principle, and we regularly ride and love bikes equipped with them. Telescoping forks do have limitations, however:
1. Front axle path is defined by fork angle. It’s simple; the axle slides up and back at the angle of the fork legs.
2. Braking, steering, and suspension duties are shared by a single component, and the forces involved often interfere with one another (more on this to come).
3. A telescoping fork forms a long arm - from contact patch to steering head - hanging from the front of a bike frame. Because of the length of this arm, every part of the system has to be large enough and strong enough to avoid breaking under the abuse mountain bike riders dish out.
4. Under braking, telescoping forks are inclined to dive. Anyone who has ever ridden a bike with front suspension knows this (and has an over-the-bars story to prove it) and it significantly impacts the way we ride and use / avoid front brakes while descending.
5. When telescoping forks dive, the steering angle become steeper and trail (a measure of steering stability) diminishes greatly, making the bike less stable. For example, a downhill bike starting at 62° will - at full compression of the front - end up at approximately 73°, with a reduction in wheelbase of over two inches.
6. Under harsh impacts and when braking hard, telescoping fork bushings experience loads that prevent them from sliding up and down freely. We feel this as stiction, poor bump compliance, harshness, and less predictable handling.Although these aren’t deal-breakers, for bicycle design teams it has been a constant challenge to do something about the limitations of telescoping forks, and there is only so much that can be done before the results of their efforts hit a plateau. Riders have witnessed that plateau for many years, as innovations in fork design nowadays offer at best a few percent of performance gain per year.