Motorcycle front suspension systems:
Traditional problems and alternative solutions
A telescopic history of suspension
Telelever and SaxTrak
Britten's girder forked parallelogram
Pierluigi Marconi and the Bimota Tesi
James Parker and RADD/RATZ
Bakker's QCS
Conclusion
Bibliography
reprinted here by permission of the author,
Gen M. Kanai
Photos sourced by Chris, comments.
Last modified 96.09.01
Imagine riding a motorcycle. You are motoring along and see a turn up ahead. You squeeze the front brakes to slow down and immediately the forks compress and you are thrown slightly forward. As you reach the turn, you let go of the brake and the bike wobbles slightly, a pogo-effect universal under these conditions. As you accelerate through the turn you see a dog in the road up ahead. You immediately grab the brakes in order to do an emergency stop. The weight of you and the motorcycle is thrown forward onto the front wheel as the forks are compressed. Steering becomes heavy and the wheel starts shuddering. You finally come to a stop and the dog looks quizzically at you.
The key to building an excellent motorcycle is to hold the parts of the bike together in a desired relationship. Certain parts must move in certain ways and others must be rigid. In the front end of a motorcycle, the steering head must turn in a horizontal plane moving the wheel at the same time. Crucial information in the form of energy must be transmitted from the road to the rider. A rigid system will conduct more of that vital information to the rider than a flexible one. A stiffer system will make a more confident rider and a more competent bike.
The forces that interact between motorcycles, riders and the road are
significant. With horsepower transferred between the road and the motorcycle
through small patches of rubber, acceleration, braking, cornering and suspending
a bike over uneven terrain can flex even the stiffest modern designs. The
alternative front suspension designs discussed here have made significant
efforts to go beyond the status quo, to revolutionize motorcycling instead
of evolving upon the present technology. All make an effort to separate
suspension and braking, and all claim to increase rigidity and stability.
In reality, all of these ideas are important steps towards breaking the
dominance of telescopic fork usage on modern motorcycles.
The main functions of a motorcycle's front suspension are: to guide the front wheel, to steer, to spring, to dampen, and to provide support under braking (Brooke, 1993:71.) By design, telescopic forks have a tendency to dive, twist or bend under braking forces. When suspension demands are placed on forks in addition to braking, the limits of traditional forks are obvious. Telescopic forks cannot separate steering and braking forces. Forces must travel up long, thin tubes to headset bearings and then back down to the frame, certainly not an ideal system. The whole fork and wheel assembly must be steered in and out of turns. Often road irregularities coupled with flexible, heavy forks create dangerous oscillations in the forks and frame. Forks not only weigh a significant portion of the bike, they also place much of that weight as far from the center of gravity of the bike as possible. The force of the loads requires that fork legs must be strengthened, bearing areas widened and frame structures enlarged in an ever-downward spiral towards heavier and bulkier systems. The alternative front suspension systems discussed herein address these problems in innovative fashions. Discussed are Hugh Nicol's Telelever, Nigel Hill's SaxTrak, John Britten's girder, Bimota's Tesi, Nico Bakker's QCS, and two systems by James Parker, the RADD and RATZ.
A telescopic history of suspension
The first motorcycles were bicycles with small engines thrust into the frame. Suspension systems were developed to keep wheels on the ground in the face of uneven pavement and higher speeds. The traditional telescopic fork came from a 1935 BMW design that included hydraulics. After BMW, Norton developed a similar system in 1939, Matchless in 1940 and Ariel in 1941 (Ford, 1989:65). The main benefit of telescoping fork systems of the early era was hydraulic damping, far superior to the friction damping systems used to that point in leading and trailing link systems. While friction dampers provided high initial friction and less with greater wheel travel, hydraulic damping provided the opposite, a boon to keeping the wheel on the road. Modern iterations of BMW's 1935 design are built with modern materials and CAD/CAM systems but remain essentially the same. Refinements in bearing technology, metal anodizing, metal strength, spring technology and composite materials all help to create modern telescopic forks which can handle extreme loads. Yet there are many inherent problems with telescopic fork suspension systems for motorcycles.
Because of a common heritage, traditional motorcycle front ends have much in common with bicycle systems, including a steering headset and forks. Key drawbacks to motorcycle front suspension systems as we know it today are structural. A design developed from bicycle technology, even modernized with new materials and improvements, is hardly adequate for the power available in today's modern machines.
Tracing the path of loads from the front tire, inherent flaws in traditional forked suspension systems are revealed. Forces acting on the tire and wheel must be transmitted up along fork tubes, (essentially 30 inch levers) through the steering head bearings, and back down into the frame. This long path for the forces induces extreme loads on the fork tubes and steering head bearings. Forks under extreme loads often twist, bend back, forth or to the side. This flexibility is very undesirable, especially at extreme occasions when one needs rigidity most. Even with the advent of modern materials, bracing and CAD, motorcycle suspension is still a copy of a pair of lowly bicycle forks.
One gradual trend motorcycle design has been moving towards wider wheels and tires. Early motorcycles had tires not much wider than bicycles while modern motorcycle tires are often 190mm wide or larger than tires on small cars. Traditional fork systems show other drawback here as forks are inherently wider than the wheel and tire combination. As tires get wider to give the rider a larger contact/traction patch, fork tubes must be strengthened to deal with the forces of braking and steering a motorcycle. As fork tubes diameters are increased for strength, the steering head bearings must be placed farther apart to deal with the increased leverage power of the fork, tire and wheel combination. Thus the steering head grows taller, raising the center of gravity and placing more weight higher. This becomes a vicious cycle as traditional telescopic forks must be designed heavier, taller and wider than previous systems, all attributes unwanted by any motorcyclist. All of the systems discussed here have lessened or changed load bearing surfaces to rotational bearings from linear systems to reduce stiction. Most of the designs are lighter overall and carry the weight at a lower center of gravity, enhancing stability and ease of turning.
In recent decades, motorcycle manufacturers have moved towards gas-charged mono-shock systems to suspend the rear ends of many motorcycles. In fact, mono-shock rear ends are de rigeur on everything but old-style or inexpensive bikes. One of the main reasons for moving towards a single shock rear versus the twin shock design of old was developments in shock technology. The main drawback to running twin rear shocks was that it was very difficult to get both shocks to do the same thing at the same time. It was also more compact, lighter and cost-efficient to use one shock in place of two. Developments in nitrogen-charged coil shocks made monoshock rear ends a reality for most motorcycles today. Why did manufacturers not hold the same ideals for the front end? Forks are springs with oil, dated technology in comparison to the gas-charged monoshocks they developed for the rear end. Even with progressively wound springs, adjustable preload and damping, two forks are very difficult to setup identically. All of the alternative systems discussed in this paper have moved to front suspension with gas-charged monoshocks resulting in lighter and more adjustable suspension, taking advantage of the extensive research and design which has gone into the modern gas shock.
Another development that all of these alternative suspension systems use is that they have discarded the traditional frame. Even today, many motorcycles are built using trellis or cradle frames, a nod back to the early history when motorcycles were bicycles with motors. These designs all use the engine as an integral stressed part of the frame. Not only has this new development in design increased rigidity, it has moved weight from the extremities of the bike in towards the center of gravity.
Probably the most revolutionary aspect to all of these alternative suspension designs is that they all make attempts to separate braking and suspension, traditionally intertwined in telescopic forks. For the racer, this means more effective braking as the suspension always has 100% of its travel devoted solely to suspension while braking is absorbed into the frame.
Telelever and SaxTrak
The systems on the BMW R1100 series motorcycles and the Saxon-Triumph 900 BEARS racer are very similar. Both the BMW Telelever and SaxTrak front suspension system, designed by Nigel Hill, look deceivingly similar to traditional systems at first glance. The "forks" on the SaxTrak are merely thin-walled cast alloy sliders which ran first on linear bearings and now on hydraulic fluid. The "forks" have no internal suspension systems and are used only to place the wheel in front of the engine, and to operate the external shock. The shock absorber is a modern gas-charged monoshock whose top mount is attached just behind the steering head. The bottom mount for the shock is attached to an A-arm steel wishbone which is mounted to the frame on eccentrics. The top/front of the A-arm is attached to the "forks" via a large ball and socket . The top of the "forks" and steering head is clamped by a billet aluminum triangular triple clamp three inches thick, easily twice as large as is found on production street motorcycles.
Nigel Hill's Saxon-Triumph is not only a technological step beyond traditional forked racing motorcycles, it allows for a faster motorcycle. The separation of steering and suspension means that a racer can brake and know that suspension travel is not being used up at the same time. Practically, one can brake later and harder than with a conventional setup, with better roadholding, lowering lap times and winning races. Alan Cathcart has proven the benefits of the SaxTrak with wins in the BEARS series (British, European and American Race Series) one week after the debut of the bike (Cathcart, 1994).
BMW's Telelever front suspension is very similar to the SaxTrak system and was designed by Englishman Hugh Nicol in 1981. The Telelever forks are very long in comparison to the SaxTrak and BMW does not use any anti-stiction systems in the sliders besides oil to lubricate the sliding surfaces. This combination makes for comparatively y weaker rigidity and promotes stiction although not nearly as much as is found in traditional telescopic forks. The differences in the systems are acknowledged in focus: one bike is a purpose-built racer and the other is a production motorcycle for mass consumption.
Telelever and SaxTrak both work to separate suspension and steering with a combination of fork tubes and swingarms. Both systems use the engine as a stressed member, an a modern gas-charged monoshock mounted on an A-arm . The Saxon-Triumph mounts the A-arm on the frame with an eccentric to make steering geometry changes easily and uses either linear bearings or hydraulic pressure to lessen stiction in the tubular sliders. These system's benefits of traditional telescopic forks are much greater rigidity due to the suspension's A-arm design and wide mounting area. Braking and suspension force paths are shortened to the frame through the A-arm and both bikes can separate suspension and braking forces. The Saxon-Triumph has ease of geometry changes and both bikes look like tradition bikes but aren't. While the Saxon is a limited production racer and has proven itself beyond merely the alternative front end, the BMW has also been well accepted by the purchasing public. These bikes have made significant strides by their mere existence and design. Seemingly traditionally forked, these bikes are the interim step towards more radical alternative designs for front suspensions on motorcycles.
An informal survey of BMW owners who are using Telelever have some strong comments about Telelever.
I have been riding and racing for 53 years and have never found a front end as remarkable as the Telelever. No dive and exceptional control under any conditions. To me it is superior to the RADD or any other type because of it's simplicity. John Goodpaster (bsajohn@pla-net.net)
I think that by experimenting with Telelever and a combination of rake and trail, you could have the perfect suspension. I have 35,000 miles on the clock and I've had no degradation in performance whatsoever. Compare that to any conventionally sprung bike--new fork springs/shock notwithstanding. No fork oil. No compressed air. No leaky seals. Guess you can tell I'm pleased. Sam Taylor D'81 (taylor@hooked.net)
The suspension is smooth under almost all conditions. I am surprised that it moves and handles so easily (short wheelbase effect) and yet is so stable (long wheelbase effect). I think the suspension gives it more stability and also better handling. Quite a feat. Stephen (dali@ipof.fla.net)
Fabulous. More responsive than forks. Responds to minor ripples during braking/ cornering. Stable during impact/ cornering situations. True anti-dive properties. Aaron Burns (aaronb@acm.org)
Another desirable effect of this front suspension is noticeable when carrying a passenger. With the Telelever, the passenger is not thrown forward much when the brakes are applied hard. This makes braking much easier for the rider, because he does not have to brace against the weight of the passenger against his back. Manuel Helzel (mhelzel@mail.transdata.ca)
The Telelever is arguably the finest feature of the bike, works completely as advertised, and is the most elegant and robust solution to motorcycle front suspension problems since the telescopic fork was first applied to [production] motorcycles. Its only shortcoming as far as I'm concerned is the quality of the shock itself, which is easily (if not cheaply) rectified. I can't picture myself riding a non-Telelever machine in the future. John Dancoe (jdan@msp.com)
God, I love it. All bikes should have front ends this good. I can only compare it to standard forks, but Telelever is far, far, better. I won't go back to standard forks. Neil Kirby (nak@gwe486.cb.att.com)
Britten's girder forked parallelogram
John Britten recently died of cancer in late 1995. Although his death
is considered by some to be the greatest loss to modern motorcycling, his
legacy lives on in his V-1100 supertwin race bike. For most of the motorcycles
featured in this paper, their alternative front suspension systems are
their raison d'etre. Not so for the Britten. While the Britten has an alternative
front suspension system, it has a whole host of other technological marvels
as well.
The first iteration of John Britten's race bike used a traditional White Power upside-down telescopic fork. In a move for more rigidity, suspension geometry flexibility, and the ability to separate suspension and braking forces, Britten created a new front end. Britten's handmade alternative front suspension is a modern redevelopment of Norman Hossack's girder/wishbone parallelogram suspension or systems designed by Claude Fior. The Hossack design was an update of the Vincent Girdraulic fork which itself was an update of systems used at the dawn of motorcycling (Alan Cathcart, Superbike Magazine, January 1993). This fourth design iteration was chosen, much like the SaxTrak, because of the versatility of the geometry. But it is a girder fork nonetheless.
Britten had four reasons for scrapping the proven race-quality White Power telescopic fork. He wanted to eliminate sliding friction under braking, raise rigidity, create an adjustable system, and reduce weight. While achieving all of these goals, Britten also managed to reduce wheel chatter common on telescopic forks, enhance braking, and improve handling (Cameron, 1992:36).
Because the girder design uses rotational bearings in place of telescoping bearings on traditional forks, bearing area and motion is significantly reduced and stiction under braking is almost eliminated. The telescoping action of traditional forks means that the front wheel is constantly accelerating or decelerating relative to the bike itself. This relative motion of the wheel and tire must either be absorbed by the tire, the fork or the brakes and often manifest itself as a "chatter" in any or all of those components. The wide expanses of carbon fiber and the girder design assure that unlike traditional systems, the front wheel position relative to the bike is constant even with extreme suspension movement. This creates a more stable platform under extreme forces (better braking) and a more direct feeling as rigidity is increased (better handling).
In order to create an adjustable system, Britten knew that a double wishbone system would be the most flexible design. Either length or angle of either wishbone in the parallelogram could be changed to affect the handling of the suspension. Britten's system can be set up for no dive under braking, pro-dive or anti-dive or a combination of any of these. At the moment current racers, having grown up on telescopic forks, like the reassurance of dive under braking. Thus Britten has set up the forks currently to dive for the first 80mm of travel and then rise for the last 40mm (Cameron, 1992:38). But as racers begin to understand the strengths of Britten's design, the fork geometry can be setup for any desired action: constant wheelbase, pro-dive, anti-dive, no-dive or any combination of these. Single wishbone systems, such as the Bimota Tesi, are not nearly as adjustable by design. The two purpose-built racebikes discussed here (the Saxon-Triumph and Britten) both have adjustable steering geometry to make a bike that can be competitive at different kinds of racetracks. By design, materials and construction, Britten was able to lighten the weight of the whole front end, reducing polar moment and making for lighter steering and better handling overall.
The Britten girder fork also has another key benefit it shares with all of the alternative suspension systems discussed in this paper. It too suspends with a modern nitrogen-charged Ohlins monoshock, probably the best developed if not most researched suspension device made. Thus it too does away with the problems of trying to make both forks in a telescopic system do the same thing at the same time. The one shock is easily adjustable, accessible, rebuildable, and lighter than the suspension systems held within the fork tubes of a traditional system.
The faults in the Britten girder parallelogram suspension are few. One issue in common with the SaxTrak and Telelever designs discussed above is that the braking forces do not have the shortest or most direct path to the frame. In all three cases, forces acting on the tire and wheel must travel some distance up mock fork tubes or a carbon fiber girder to reach arms that attach to the engine or frame. The later discussed RADD and Tesi systems have the shortest path possible for braking forces into the frame and do so at a lower height on the bike, lowering the center of gravity and easing steering. The low weight of the Britten system in addition to the rigidity of the materials make that fault almost imperceptible. Britten has shown us that an updated version of the girder fork that was used at the dawn of motorcycling is still a viable option that has many benefits of traditional telescopic forks.
More than any other motorcycle in the world, the Britten V-1100 showcases the integration of a host of design features that, given a clean sheet of paper and an unlimited budget, designers would unerringly adopt as the best way to achieve a given design target. Features that for commercial or marketing reasons, they are simply unable to adopt themselves. Alan Cathcart, Superbike, May 1993, p.42.
Pierluigi Marconi and the Bimota Tesi
Bimota is a small Italian firm which designs motorcycles around engines
from other manufacturers. The unique aspect of the Tesi is that it is a
hub-steered motorcycle, having more in common with the articulation of
a car wheel than with forks on a bicycle. Conceptually, the front end of
a Tesi looks like a set of motorcycle rear swingarms moved to the front
and bowed to accommodate approximately 30 degrees of steering lock for
turning the front wheel.
The front swingarm is kept at hub level and attaches
to the "frame" of the motorcycle directly behind the wheel. One
of the most important design benefits of the Tesi is that the path for
any forces entering the motorcycle from the front wheel have the shortest
distance to the frame. The frame in this motorcycle is not a traditional
cradle which has been the design paradigm since the beginning of motorcycling.
Bimota has a pair of milled aluminum plates which sandwich the Ducati engine
on each side. Shaped like an upside-down U, the ends of these plates accept
the front and rear swingarms. Using the engine itself as an integral part
of the frame is yet another revolution in this motorcycle design. What
this new front suspension has done is to change where and how much weight
is up front. The Tesi uses significantly less weight to achieve a stiffer
steering and suspension package and places the weight low. Steered weight
is extremely reduced as the only steered mass is the tire, wheel, brakes.
A telescopic fork system and frame must support the extreme braking and suspension forces in addition to the weight of the rider. Most modern motorcycle front ends weight close to one hundred pounds or often a quarter of the total weight of the bike. In a traditional system, this whole mechanism must be turned to affect a change in the trajectory of the bike. Steered mass is very heavy as faster motorcycles need stronger, stiffer and bulkier telescopic forks.
The benefits of hub-center steering are many. The main benefit is a true separation of braking and suspension forces and overall rigidity. With telescopic suspension systems, braking forces are mated to suspension forces. When a rider uses the front brakes on a traditional bike, the front forks are compressed. In extreme or race situations, to reach optimum or threshold braking potential is to often use up nearly all of the suspension travel. This makes the bike incapable of following the road if it is uneven and makes for very heavy steering. The short, direct force paths from the front tire to the frame are the most efficient system for getting power from the road to the bike and rider. Bimota chief engineer Pierluigi Marconi has tested the Tesi design as being 25% more rigid than a comparable traditional fork. Thus, this system is stiffer.
The first and second prototypes of the production Tesi that was sold in 1991 were developed on a Honda VFR400 platform using hydraulic steering actuation and a composite frame. Bimota realized that hydraulic steering was the problem with the prototypes. Thus for the 1991 production model, powered by a Ducati 851 fuel injected V-twin, mechanical steering linkages were used. (CW 5/91)
In place of the traditional axle is a horizontal non-rotating trunnion tube through which is vertically set a kingpin, to serve as the axis so that the wheel can be turned for steering. Large bearings around the trunnion allow the wheel to spin on a vertical axis. Horizontal bearings around the kingpin allow the wheel to steer. Tilting the kingpin allows adjustments of rake and trail. All of the steering is actuated from the handlebars with a maze of levers, spherical and rotational bearings, ten all together. Attached to the main swingarm are twin lever arms which actuate a gas-charged monoshock.
Unfortunately, the actualization of this hub-center steering system was not optimized. Although the hydraulic steering linkages were dropped for mechanical linkages, the sheer number of moving parts resulted in a certain amount of slop. Four spherical joints and six rolling bearings must be moved to steer this bike. The inclusion of 10 bearing surfaces made for significant flexibility which is undesirable. Much of the design problems with steering probably had to do with the fact that Bimota had to design the steering system to work with an engine not optimized for the situation.
While the hub-level front swingarms had the shortest force path to the frame, they had to be bowed to allow the wheel to turn. This bowing coupled with the diameter of the swingarms meant that the front end of this motorcycle was much wider than a forked unit. While riders do not complain of dragging the swingarm in turns while leaned over, one liability of this design is the width of the system. Steering is also further complicated by the trunnion tube hitting the swingarm at either extreme. Thus, compromises must be made to allow steering as well as rigidity.
The limited number (300) and exotic price ($40,000) of this motorcycle relegated it to only a few. Yet it served to prove the viability of a hub-center steered system and the benefits of truly separating braking and suspension forces. It was and continues to be an influential design, heralding the emergence of hub-center steered designs.
James Parker and RADD/RATZ
One of the most influential motorcycle suspension designs is the RADD system designed by James Parker licensed to Yamaha for the GTS1000A. Holding the most theoretical promise, it is a true hub-center double swingarm system which separates braking and suspension. What makes the RADD design different than the Tesi aside from the single-sided nature of the suspension swingarm is that two A-arms are used, the lower to suspend and brake, and the upper to steer. Unlike the Tesi swingarm design, this has the advantage of parallelogram adjustability as seen in the Britten or SaxTrak design as well as higher rigidity.
Parker went through many prototypes before working with Yamaha on the GTS and the key was the telescopic steering column which allowed the most direct inputs on the steering swingarm and is a stronger design solution than the scissors-link used on Nico Bakker's QCS machine and the Britten. The bane of a cornering motorcyclist is "bump steer" or the ability of road irregularities or suspension movement to steer the bike itself. Many prototype alternative front suspension systems by different designers had problems with bump steer due to intricate or hydraulic steering linkages. Parker's solution was direct steering control through the telescoping steering column.
Essentially, two swingarms project forward from the frame mounted on
radial bearings. At the front ends of each of the swingarms are spherical
bearings that help to control the movement of the wheel. Right here, benefits
over telescopic forks are visible. Bearing surface area is radically smaller
and bearing movement is less, creating almost imperceptible friction. No
longer are telescopic tubes moving against each other creating sliding
friction. The lower arm has a modern gas-charged shock mounted on the top
of the arm, connected to the frame. In this manner, the lower arm's movement
is solely to suspend the front end. Frictional movement is significantly
reduced and rigidity is significantly increased. The steering arm's upper
end is connected to a telescoping steering box which is connected to the
handlebars at the upper end of the system. Below the steering box is another
single-sided swingarm, smaller and lighter than the suspension swingarm
because it only needs to be strong enough to steer and carry the weight
of the rider. At the bottom end of this swingarm is another spherical bearing
that carries the wheel. The brake caliper is mounted to the steering arm
and a dished wheel with brake disc is the last component.
With Parker's design, there are many benefits as discussed with the other systems. Steered mass is halved as all that needs to be steered is the wheel and the upper steering swingarm. Rigidity is increased significantly due to the nature of the suspension swingarm. A wide area at the frame mount places loads in a much more direct route than traditional systems which send forces up a set of telescoping levers, through a pair of roller bearings at the steering headset and back down the frame. Suspension travel is essentially relegated to one plane, and extreme travel does not cause changes in rake and trail as experienced with traditional forks. Center of gravity and weight is lowered, making a more friendly, easy to steer system. And finally, the single-sided nature of Parker's system makes for easy wheel removal. The benefits over traditional forks are numerous and practical.
Although the GTS was not considered a commercial success in the US, it certainly was not due to any mechanical problems with the suspension. Traditional fork systems have been in use for the entire life span of most motorcyclists alive today. While the GTS does not demand a new riding style, to get the most out of the design is to revolutionize the way one rides as well. This front end, coupled with Yamaha's excellent ABS system is the potentially the most potent and stable braking platform on two wheels. The separation of braking and suspension means that a rider can brake at a threshold level while knowing that the suspension has 100% of its travel available to deal with road irregularities. Traction and handling are no longer mated to each other. Stability is the paradigm. In the same way suspension has revolutionized bicycling both on and off-road.
Forks are a lever, and no matter how good the forks are, they still act like a lever on the frame and multiply the load from the front wheel to the chassis. If the front wheel of a motorcycle that has traditional telescopic forks is loaded with 600 pounds, that 600 pounds translates to 1800 pounds of load on the frame. If the forks of that same motorcycle were to be replaced by the RADD system, a 600 pound load would be fed into the frame at only 600 pounds. [In the RADD system], the load of the motorcycle and almost all of the loads that are generated by the front wheel essentially travel into the chassis through the lower arm. The lower arm is in-line with the load so there's no lever arm involved. (James Parker, speech at RPI, 10/14/95)
According to Parker and owners of the GTS, the RADD front suspension not only solves the classic lever problem, but works much more efficiently and rigidly than the traditional system under heavy braking. Comments from an informal poll of GTS owners reveal similar opinions.
I've found the front suspension on this bike to be everything I expected and more. I've never ridden another motorcycle that inspires the same cornering confidence that the GTS provides. Unlike most bikes, which feel less and less secure as lean angle and cornering speed increase, the GTS just never seems to use up its full capacity to stick through even the bumpiest corners. Paul Taylor (72002.3603@CompuServe.COM)
The most common criticism of [the GTS] was that it reduced feedback and feel through the handlebars. That's probably partly true, but I think that it suspended so well that it unnerved long time riders who were used to telescopic forks and had trained themselves to understand and work with their inherent quirks. It wasn't nearly as complex as it was made out to be, and it provided more stability and more structural integrity than the Telelever. It really does feel different--and I believe some riders would never get comfortable with it--but if you are willing to trust and adapt to it, it's head and shoulders better than a conventional fork, and potentially superior to Telelever. Mike Knezovich (mike@spyglass.com)
Parker's effort since the GTS has been to create a purpose-built roadracing bike developed around a Yamaha two-stroke engine. The RATZ (mating RADD and the Yamaha TZ 250) roadracer has addressed all of the problems that the RADD system on the GTS had. Unfortunately, Parker's relationship with Yamaha in developing the GTS was not as close as it should have been. Problems that came up with the GTS included over engineering of the swingarms, making them unnecessarily heavy and wide. Slow-speed steering was theoretically better because of halved steered mass over traditional systems, but Yamaha's front wheel was again over engineered and much heavier than was necessary or safe. A better swingarm could have been both lighter in weight and stronger by design, but Yamaha engineers erred too far on the large side. The main problem with the wide front suspension swingarm, other than weight and bulk, was that in extreme cornering situations it is possible to scrape the swingarm itself on the ground. A thinner, stronger and higher-placed swingarm could work as efficiently and give the rider as much lean as needed and that is exactly what Parker did on the next design. He also eliminated a pair of flexible couplings at either end of the steering tube to quicken steering and lighten weight. (Karr, 1994:24)
Another Achilles heel for the GTS, and all of the designs discussed here, is tires. While significant research was purportedly done to test tires on the GTS, GTS owners believe that this bike is much more sensitive to tire design differences than any other bike. Parker believes that once tire technology has been re-examined to be developed specifically for the different needs of swingarm suspensions, more benefits will be seen from the suspension design. As it stands today, tire design and construction plays a critical role in helping to suspend a traditional telescopic fork and modern radial designs are iterationally optimized for these systems, not for any of these new designs which place different loads on the tire. Parker believes there are no inherent problems with the double swingarm suspension system and with even a fraction of the research and design that has been devoted to telescopic forks should bear out his beliefs. (Interview with James Parker, 5/17/95) Parker's new effort is RAV, or Radically Advanced Vehicles, a company dedicated to building an American sportbike. Using lessons learned from the RADD and RATZ systems, Parker hopes to design a bike with an engine specifically built for the front end design. He also hopes to cause a revolution in tire manufacturing to build tires that will be developed specifically for the new demands of these alternative suspension systems. Tire design, much like motorcycle design, has been a evolutionary development since the advent of radial construction. All of Parker's efforts are, like Britten's, an attempt to look at motorcycles and riding from a fresh perspective, a tabula rasa. Instead of updating an iteration of a previous model, Parker chose to examine the benefits of twin a-arm steered upright front suspensions systems and decided that the benefits vastly overweighed the modern iterations of telescoping fork systems.
Bakker's QCS
While very similar the Parker's design, Dutchman Nico Bakker's Yamaha QCS had a few important design differences to highlight. Much like Parker's GTS, Bakker's machine used an FZR 1000cc Yamaha engine and a front end almost identical to the GTS. But Bakker's bike used a scissors-link as is found on airplane landing gear instead of a telescoping steering column. The other difference is that Bakker had more linkages actuating the front monoshock than the GTS design. These subtle differences made for a product that is not as refined as the GTS. Low speed steering was hampered by the scissors-link which added steering deflection because it was not attached to the frame in any significant fashion.
Bakker's effort was a limited-production of 30 hand-built bikes. While his execution of the twin-swingarm, steered-upright front suspension was less effective than Parker's design, it shows the weakness of the scissors-link as a steering member. Curiously, the Britten uses a scissors-link in its steering system with excellent results.
Conclusion
The main stumbling blocks to further development of these alternative systems is the conservative motorcycling public. While some of these bikes are high-cost, low-production exotic machinery, it is telling that the BMW's Telelevered bikes have been a commercial success when the Yamaha GTS has not. Setting aside differences in audience and brand loyalty, the BMW looks deceivingly like a traditional motorcycle whereas the difference of the GTS is obvious. Not only do these alternative designs demand an open mind when assessing the bikes, they demand a new riding style as well. The result is a better motorcycling experience but not without efforts to change the way one looks at or rides bikes. Those who have made efforts to try the new technology know that the future lies beyond telescopic forks. Yet it is telling that a significant portion of motorcyclists currently desire technology from the early part of this century in the form of pushrod engines and dated designs. What all of these alternative designs have done is to open the door for further research into alternative systems not only in suspension but in frame, tire and engine design. The immediate future of motorcycling will see a move away from traditional frames as we know them and engines as stressed members of frames will become the norm. When the designs of the other parts of the motorcycle have been revolutionized as these suspension systems have been, we will see a very different, better motorcycle.
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