Motorcycle Fork Design

Since I started working on alternative motorcycle front-suspension systems in the early '80s, I've carefully analyzed other alternative systems and studied perhaps 100 different patents, inventions, and prototypes in this field. At the same time I've looked closely at the telescopic fork and the many changes and improvements made to it over the decades.

The telescopic fork clearly still dominates motorcycle front suspension. Does that mean there’s no better alternative and that the weaknesses that originally prompted me to develop my alternative have been cured? No. Although detail improvements continue to enhance performance, in many respects the fork of today looks and works very much like the fork of decades past.

The telescopic fork has its strong points. It's conceptually simple, and its simplicity and low cost mean it's easily adaptable to models ranging from minibikes to motocrossers to superbikes. With the telescopic fork, manufacturers need only design a chassis with an appropriately positioned and structurally sound steering head; the fork provides the complete front suspension and is often available ready to use from an independent supplier.

But the very simplicity that provides these benefits keeps the telescopic fork from being the best suspension for a high-performance motorcycle for several reasons.

1. The fork acts as a lever. This leverage acts on the chassis, with front-wheel loading multiplied as much as 300 percent at the steering head. Engineers try to minimize loads, but in this case they have to accept multiplied loads.

2. The fork acts as a spring—but not the good kind. The tubes bend under certain loads and spring back with no damping, which reduces steering accuracy and causes some loss of stability.

3. The fork acts as a pendulum. When the fork pivots as you steer, the entire suspension moves. When the weight of the wheel, the brakes, and the suspension starts pivoting, headshake and tank-slappers are sometimes the result. This is perhaps the fork's biggest stability compromise.

4. The fork accentuates and promotes brake dive. Any suspension reacts to weight transfer under braking, but weight transfer accounts for only part of the brake dive we experience on a forked bike. As the front brake is applied and the wheel slows, the motorcycle continues forward against the fork springs, which compresses the fork and compromises the suspension quality of even well-engineered forks under braking.

These four issues aren’t the only problems that even the best forks carry around with them, but they outline where things might improve. And they show that the fork is flawed. What developers of alternative front suspensions have tried to do is eliminate or minimize each of the telescopic fork’s downsides.

I won’t go into the details of the alternative systems, but there are front-end arrangements out there that almost completely eliminate these issues. So if the telescopic fork is so flawed and there are better alternatives, why does it continue to dominate?

First, because however good a new system might be, it won’t be as simple. Cost is a factor too. Looking at an unfamiliar alternative, a manufacturer highly motivated to keep it simple and cheap—which includes most manufacturers—will likely stick with what works well enough.

Next, imagine if another system was proven to be more stable, and safer, than the telescopic fork. That might lead to a lot of questions like, “Why are you still making bikes with that less-stable telescopic fork?” In a litigious society, that’s a pretty strong motivation to leave things as they are.

Finally, understanding the fork’s strengths and weaknesses, and demanding changes, takes at least a basic understanding of engineering, an understanding that’s less and less common among consumers in our de-industrialized Western nations. So we may well be forever “forked,” but let’s not pretend that the fork is therefore the best possible solution forever.