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Common Tread

Why are there no alternatives to the telescopic fork front suspension?

Aug 02, 2019

The first motorcycles had the same simple, rigid front fork you’d see on a bicycle. Ever the innovator, Alfred Scott built the first known telescopic front fork in 1908. However, for the next few decades the sprung telescopic fork was just one of many front suspension arrangements tried by intrepid engineers and entrepreneurs.

The beginning of the end for that diversity came in 1935, when BMW introduced the R12. That was the first production motorcycle to add internal hydraulic damping to a telescopic front fork. Ironically, BMW was one of the few OEMs not to become enthralled with that design when civilian production resumed after World War II. BMW favored the Earles fork from the mid 1950s until the late 1960s, and more recently it’s often favored either a modified Hossack design, or a Saxon-Motodd fork, under their "Duolever" or "Telelever" trademarks.

BMW Telelever
The BMW Telelever front suspension. BMW photo.

In the last 50-plus years, the telescopic front fork has become so ingrained across the motorcycle industry that now even BMW is careful to make its funny front ends look as much like a conventional fork as possible.

1905 Indian
This 1905 Indian had a bicycle-style front fork because, in 1905, motorcycles were bicycles with motors. The main reason we’ve stuck with that basic architecture for the last 114 years is that we’re used to it. Photo by Mark Gardiner.

However you choose to accomplish it, suspension’s a good thing. It’s far better to have the wheels track over dips and bumps while the chassis and rider maintain a relatively smooth trajectory. And because one of the fork’s best points is that it minimizes unsprung weight, the modern forks with ultra-low-friction coatings do a great job of keeping a front tire in contact with the road (at least when a motorcycle’s more or less upright).

But the front fork as we know it is a terrible way to attach a front wheel to a motorcycle chassis.

“Heresy!” you cry. But suspend your disbelief...

Motosacoche
An early attempt to add wheel travel and comfort to a bicycle-style fork, by the Swiss motorcycle pioneers at Motosacoche. If you can figure out how this suspension works, let me know. Photo by Mark Gardiner.

Problem: Bump forces versus braking forces

The main problem with conventional forks is that they can’t separate bump forces from braking forces.

Using a high-end Öhlins FGR300 superbike fork as an example, each leg has an overall length of 750 mm and provides 130 mm of suspension travel (call it 30 inches of length for five inches of travel). Each stanchion (the parts held in the triple clamps) is a massive alloy tube, resulting in a weight for both legs of nearly 20 pounds. That’s a lot of steered mass.

Next time you’re looking at a typical alloy beam-framed sport bike, flick the middle of the beam with your fingernail. You can tell by the sound that the beam itself is thin and hollow to reduce weight. But look at the steering head — it’s a massive casting. That massive structure isn’t needed to withstand the riders’ steering inputs. It’s not even needed to handle the forces imparted when Lemmy, in mid-wheelie, spots a cop car and slams the front end down.

Your bike’s massive steering head is needed to withstand the forces imparted by the front brake, which is the most powerful component on a modern sport bike. (If you don’t believe me, compare the distance it takes to accelerate to 100 mph and the distance it takes to stop from 100 mph.) So you have your front brake, which basically applies a force to the ground, at the front contact patch, which acts on the motorcycle at a point three feet away, up at the steering head. The stanchions, which are long levers, can’t deflect much under load either, because the suspension still has to absorb bumps, even though most of the travel is used up under hard braking.

Britten
This Britten used a carbon-fiber Hossack-style girder. Although it has many advantages over a telescopic fork, it still makes a hash of transferring those brake forces. Photo by Mark Gardiner.

As a result, a conventional fork dives under hard braking. As weight’s transferred to the front wheel, the fork springs compress. This uses up fork travel that would otherwise be available for bumps, which is bad enough. But wait, it gets worse...

Brake dive also shortens the wheelbase and changes the rake angle. In a perfect world, engineers would certainly rather not change those parameters in mid-corner!

Over the years, pretty much every OEM has experimented with systems to minimize brake dive, peaking in the 1980s, with Honda’s TRAC (Torque Reactive Anti-Dive), Suzuki’s PDF (Posi-Damp Fork) and Kawasaki’s AVDS (Automatic Variable Damping System) among many others. Most worked — to one degree or another — by interfering with the flow of hydraulic fluid. All were ultimately abandoned because the cost, complexity, and weight weren’t offset by measurable handling improvements.

Is devising a steerable suspension system that can separate bump forces from braking forces really that hard?

Ner-a-Car
This 1924 Ner-a-Car proves that hub-center-steered alternatives to the front fork were definitely considered. This was a successful motorcycle, made in the United States and licensed to a UK manufacturer, as well. Photo by Museumsfotografierer.

Not at all. Every car has such a system. When James Neracher, of Syracuse, New York, designed his Ner-A-Car in 1918, he engineered a hub-center steering system. That was one of the reasons he claimed his motorcycle was “nearly a car.”

There have been countless hub-center-steered designs since then, including some high-profile ones like Andre de Cortanze’s ELF system — as seen in the World Endurance Championship and used by Ron Haslam in the 500 GP class in the 1980s — and the breathtaking Bimota Tesi, from the early 1990s.

Bimota Tesi
The stunning (and stunningly complex) Bimota Tesi is one of the most famous modern hub-center designs. It relies on a double-sided front swingarm. Early versions relied on a hydraulic steering system, but Bimota realized that was a bridge too far, and went with this steering-arm arrangement. Photo by Mark Gardiner.

For the rest of this essay, however, I’m going to focus on James Parker’s RADD system, partly because of my personal experience with it and mainly because it nearly broke the telescopic front fork’s stranglehold on production road bikes about 25 years ago.

"R" is for "rational," not "radical"

James Parker was a Stanford-trained industrial designer who club-raced in the 1970s on some very innovative, home-brewed specials. I interviewed him at length about 10 years ago.

“Back then,” Parker told me, “forks were terrible.”

In the early 1980s, he set out to replace the fork with something better. But as primitive as those damping-rod forks were, they were better than the only real alternative, which was the ELF. Parker saw the weaknesses in de Cortanze’s system as poor ground clearance on one side and, because it had a steering arm, a tendency to bump-steer.

Parker reverse-engineered de Cortanze's system by blowing up photos of ELF race bikes and tracing them. Then he devised a collapsible steering shaft that ran down the steering axis. He dubbed his suspension system RADD, which stood for Rationally Advanced Design Development.

“I quit racing,” he told me, “when I filed that first patent. The legal costs were about the same amount as a season of racing, and I could only afford to do one thing.”

His first test mule was powered by a Honda 600 cc single. He took it to Honda's U.S. headquarters in 1984, where it piqued their curiosity.

American Honda had just signed a young rider and they sent Parker, his bike, and that kid — Wayne Rainey — out to Willow Springs to test it. Rainey was impressed, but word came back from Honda that they were committed to working with ELF and de Cortanze, who were sponsored by Honda. (Although Honda never used de Cortanze’s radical front suspension system, the excellent Pro-Arm rear suspension system was another of the Frenchman’s inventions.)

Some skeptics thought Parker's system only worked for lightweight bikes. To answer them, his next bike prototype was powered by the then-new Yamaha FZ750 motor. Parker built the chassis and a Yamaha design consultant in Los Angeles created the bodywork. In 1987, the bike — dubbed the MC2 — was shown in Milan and featured on the cover of motorcycle magazines all over the world. Yamaha was deluged with inquiries about it.

At the same time, product planners in Yamaha Europe's HQ were pushing the company to develop a flagship sport-tourer. The brief for the GTS1000 included ABS, electronic fuel injection, and Parker's RADD suspension. Yamaha handed Parker a thick dossier of all the Honda/ELF patents, and a two-year development contract. It should have been his big break, and even years later, he could not conceal his bitterness over the end result.

“I'd go to Japan for meetings,” he told me, “and they'd wheel a prototype into a boardroom. They never let me into the workshop; the guys I spoke to never had dirt under their fingernails.”

James Parker and the Yamaha GTS1000
In the 1990s, James Parker nearly succeeded in his lifelong quest to supplant the telescopic front fork when Yamaha licensed his patent to produce the now sought-after GTS1000. Photo by Mark Gardiner.

He warned them that changes made to the steering geometry would hamper the bike's handling. When it was finally launched, it was big, heavy, and expensive. Its other showcase technologies were poorly developed, too, but they weren't as visible as Parker's invention. Only a few thousand were sold. The motorcycle industry's conclusion was, “Alternatives to the front fork? We tried that, but it didn't sell.”

Long after the GTS was discontinued, the UK magazine Bike named it one of “The 50 coolest bikes of all time.”

James Parker and Mark Gardiner
About 10 years ago, I tested the most advanced version of Parker’s RADD suspension on a modified GSX-R750. Photo by Jonathon Butterman.

I rode RADD and it was marvelous

Parker never lost faith in his design and continued to improve it. Years later, I compared a stock Suzuki GSX-R750 K7 to an identical bike fitted with the third major evolution of the RADD front swingarm.

My test took place on the scrappy Sandia Speedway road course outside Albuquerque, New Mexico. There were only a couple of places where I could get over 100 miles an hour, at that only for a few seconds. The surface was riven by deep seams, bumps, and choppy asphalt. While there were no elevation changes to speak of, there were a couple of near jumps where the course entered and left a stock-car oval. I wouldn’t have wanted to race on that track, but it was a great place to test a road bike's handling.

Turn One was a 180-degree banked right, part of the oval track. Thanks to its dramatically reduced steered mass, the prototype took less steering effort and seemed more responsive to body inputs. The racing line took me across two deep pavement seams that upset both bikes; the prototype settled much quicker.

testing the GSX-RADD at Sandia Speedway
Testing the GSX-RADD at Sandia Speedway in New Mexico. Photo by Jonathon Butterman.

Next up was an increasing-radius right that led to a very tight hairpin left. At that point on the track, the prototype actually seemed to increase the length of the short chute leading up to the hairpin. Although the RADD bike dove less under braking than its forked sibling, it was easier to adapt to than, say, a BMW Telelever setup.

It was exceptionally good when trail braking. The local club-racing #1 plate holder tested the prototype and reported that he could brake later on it, even though it was equipped with Dunlop Qualifier road tires, than he could on his race bike, equipped with slicks.

Parker went to a lot of trouble to make his suspension feel like a fork. Nonetheless, the experience was totally different. On cold tires, especially, the gnarly surface of that first-gear hairpin was intimidating. It was there that I noticed the prototype's most striking trait — I could feel the texture of the asphalt. That exceptional feedback made me think, this must be what it’s like to be a really talented rider.

The cliché is that such hub-center-steered systems differ from forks in that they separate suspension forces from steering forces. A better way to think of Parker's GSX-RADD system is that is separates the fork's job into three components: braking force is transferred in almost straight compression back through the arms to the chassis (in this case, the engine as a stressed member); vertical forces are handled by the shock absorber; and steering effort, by far the smallest force, is transferred in an extremely direct way by the telescoping steering shaft.

The net result is the feedback and responsiveness of a much smaller bike with the stability of a bigger one. The GSX-RADD weighed 22 pounds less than the stock bike and allowed for easily adjustable rake and trail, variables that are very hard to change on modern race bikes.

If forks are so terrible, why does every MotoGP team still use them?

Motorcycles may be risky, but the motorcycle industry — particularly the dominant Japanese firms — are risk-averse and conservative. The fork is a terrible solution to the problem of how to attach a front wheel to a motorcycle, but it’s the solution we know, and in the limited defense of Öhlins, et al, they’ve sure perfected them. Considering their inherent limitations, the best modern forks work fantastically well.

Repsol Honda MotoGP race bike
Manufacturers have built massive and massively expensive components to overcome the inherent drawbacks of a telescopic front fork in racing, and they've done a great job. But is there a better way? Repsol Honda photo.

That best performance comes at a price: That Öhlins FG300 fork I used as an example will set you back about $12,000, and for that you still won’t actually have a fork — you need to provide your own triple clamps. They’re incredibly complex; the owner’s manual lists no less than 71 separate components (per leg) and specifies 15 torque settings on critical fasteners.

Ironically, we’re so adapted to the fork’s limitations that some of its weaknesses are now perceived as advantages. As riders, we willingly sacrifice suspension travel under hard braking in order to steepen rake and improve motorcycle turn-in. And in high-level racing, where maximum lean angles now exceed 60 degrees, the lateral deflection of those long fork legs serves as suspension over mid-corner bumps.

So for the foreseeable future, we’re just forked. But I keep hoping that some brave race team or OEM will give something like Parker’s RADD system a real chance. Once that happens, we’ll never turn back.