Legacy Motorcycle Commission Design Brief
The American Superbike
The story of the American Superbike is written in the parlance of the 4-cylinder, 4-stroke, longitudinally-mounted engine and begins in 1909 with Percy Pierce. Son and heir to the Pierce automotive concern, young Percy was smitten with motorcycles. Upon discovering the amazing Belgian FN 4-cylinder, he dedicated the full might and engineering excellence of the Pierce Automobile Company to the creation of a motorcycle that would influence American motorcycle design on the high end of the scale for the next 30 years.
The Pierce 4-cylinder, though short lived, raised the bar internationally. It also served as the archetype for subsequent 4-cylinder American motorcycles in terms of smoothness, speed, and beauty.
By the time William Henderson released his first motorcycle in 1912 under his own name, the market for 4-cylinder American motorcycles had been but tentatively established. His rather awkward 1912 machine was robust though, and ridden by Carl Stearns Clancy, was the first motorcycle to circumnavigate the globe!
The 1913 Four kept the quality of the 1912 while rectifying the cumbersome design elements to codify the graceful style of the American 4. It also formed the basis of a design language that would be expressed more fully in Henderson's masterpiece: The Ace.
When Ignaz Schwinn acquired Henderson’s company as part of his plans for a manufacturing conglomerate in 1917, it would not be long before Henderson would become restless and strike out on his own again. In 1919 William Henderson was once more in pursuit of the ultimate 4. The Ace company was his second bite at the apple.
A year after his untimely death, his vision became reality in the form of the legendary 1923 Ace XP4. The mantle had been passed to a talented engineer, Arthur Lemon, who, ably assisted by Everett DeLong, constructed the first American Superbike. Ridden to a clocked speed of 130 MPH beneath Red Wolverton, the XP4 fulfilled the promise of world-class performance and style.
A pity that Henderson had not lived to see it.
DeLong went on to engineer the Cleveland Tornado and the Century, both excellent machines with highly refined aesthetics.
In 1927 the assets, tooling, and designs of the Ace brand were acquired by the Indian Motorcycle company and lived on as the “Indian Ace.” Eventually renamed the "Indian 4,” the modified design was produced as a halo product with the last Indian 4 being produced in 1941 as a 1942 model.
In the paltry span of 40 years, motorcycle design had rapid acceleration... from bicycles with the crudest single-cylinder engines clamped to the frame, to the mighty 4-cylinder Indians that even by today’s high speed interstate standards, make solid mounts. An industrial version of the Cambrian Explosion…
The Great Gap
For an entire generation of American motorcyclists, and indeed the rest of the world, it was the 4-cylinder that reflected the ultimate in comfort, style and speed. While the American twin cylinders were at the zenith of world-class sporting motorcycles, it was the power, grace and poise of the big fours that defined luxurious motoring.
As economies of scale began to define profitability, the sheer complexity of the fours lost favor as the twin’s superior weight-to-power and relative simplicity revealed. Nevertheless, the hierarchy of the American motorcycles can be thusly summarized, and while painted with an admittedly broad brush, not inaccurately:
- Singles for lightweight, introductory models and lightweight competition.
- Twins for all-purpose middleweight transportation, and especially fierce competition.
- Fours for high-end exclusivity and luxury. The ultimate expression of artistic mechanical design.
Almost 100 years after Percy Pierce fell in love with the idea of an American 4-cylinder, Michael Czysz unveiled the Moto Czysz C1. Challenging convention at the minutest level, the C1 railed against a stagnant and degenerative American motorcycle culture, and plans for an all-out assault on world class Moto GP racing were announced. While not a luxury machine, the 2004 C1 prototype and subsequent 2008 C1 preproduction motorcycles promised a new take on the longitudinal American 4, this time in a narrow angle V.
As is all too often the case, the rules for the Moto GP formula changed, the engine was shelved, and chassis elements went on to house an electric motor that powered the E1PC model to multiple victories in electric motorcycle racing.
When word of a new American 4-cylinder emerged in 2009, It was met with equal parts enthusiasm and skepticism. Since the context of 4-cylinder American power was lost for more than seventy years, the American public was challenged to categorize the excellent work of what may be one of the greatest motorcycle designers in the modern era, Brian Case, now with Motus Motorcycles.
The Motus' V4 configuration promises power and torque with relatively simple mechanicals. Architecturally similar to the ubiquitous American v-8, the Motus uses a single camshaft with pushrod actuated valves that while on the surface may seem primitive, makes full use of the tremendous technological development poured into this formula over the last sixty years. Drawing on both the tribal and corporate knowledge of automotive performance V-8 configurations, it is an engine that is begging to be plugged into that most American of archetypes.
Now, a long, low, luxurious, and blisteringly fast homage to the Iconic Ace XP4 is possible. The Bienville Legacy Commission completes the circle.
Our Design Goals
Rather than merely a pastiche of clumsily applied vintage styling cues, this new motorcycle will be culturally and contextually relevant. Toward this end, an appreciation and sensitivity to the past without a prostration to it, brings an obligation to innovate.
But in the ever budget-conscious realm of the business of motorcycle companies, we must be freed from the manacles that constitute profitability and economic viability. Similarly, we must be freed of the immediate horizon in equally strident world of Moto GP. Without these constraints, we can perform real exploration. And then, we can inform either of our findings. Hopefully for their benefit.
Consequently, the Bienville Legacy project will have its most important impact in three areas:
- Ergonomics, and
In order to prove the viability of our concepts -- as well as the project as a whole -- an objective test must be conducted for external validation and internal satisfaction. As such, we will go racing at Bonneville.
Perhaps once-in-a-generation is this kind of experiment conducted. Thanks to the ADMCi, we can broaden the horizon of possibilities… reach is unleashed, grasp becomes attainable.
For the most part, motorcycle suspension has been a process of refinement since WWII. A telescopic fluid-filled front fork, and coil spring over rear shock arrangement has been the standard. The modern motorcycle, with its highly refined version of this system has proven the validity of this formula. But, we respectfully submit that it has done little to address it’s underlying weaknesses:
Stiction – Bushings within the telescoping elements of a traditional fork work to create free play between the two, but in fact cause minute pauses in motion, especially in directional changes from rebound to compression.
Dive – Applying force to front wheel brake discs results in a high degree of compression in the front fork tubes as the entire mass of the motorcycle and rider pivots around the abruptly introduced pole of moments at the front axle. Weight transfer vectors greatly reduce the effectiveness of the front suspension by asking the springs to suspend, while concurrently providing resistance.
Mass Centralization – Two front fork tubes filled with fluid and springs, positioned far from the steering axis and far forward compromises goals for centralized mass. Similarly, a rear suspension unit positioned to the rear behind the engine is also far from ideal.
Complexity – Multiple springs (at least 3) of different wire width, length, and diameter add weight and require two process steps to alter spring rate for front fork tubes. You must disassemble them to alter rates for the rear, and you must deal with a high level of difficulty for servicing seals, bushings, and fluid for both front and rear. Balancing the two dissimilar systems for front and rear frequently leads to compromised handling.
Wheel Trajectory – The critical relationship between steering neck angle (rake) and front wheel contact patch yields the trail value. With a linear front fork (deflection notwithstanding), trail values will always have a nonalterable trail-curve-to-suspension-travel-ratio when graphed.
Unsprung Weight – All fluid for front fork tubes is considered unsprung, as is a large percentage of the heavy steel coil spring and valving that travels with the wheels. Unsprung weight is a compromise in overall design.
Universality – Due to their complexity, front forks and rear shocks are produced by specialty companies, then adapted to specific motorcycles with varying levels of success. Proprietary suspension is the great unknown.
Our solution to these various compromises is simple. Stiction can be greatly reduced with the use of a multi-link front fork that does not rely on isolating bushings for the tubes to telescope smoothly or rake angles to counter deflection of those tubes as they vector impact forces from irregularities in the road surface to the chassis.
By separating braking and suspension systems, the weight transfer vector is lowered.
A single, centrally-located composite leaf spring for both the front and rear suspension eliminates steel coils further away from the mass center of the motorcycle.
Utilizing a leaf spring instead, its rate is determined by its material construction, width, and overall shape. The first man made spring, the Paleolithic bow, was simple and effective and lent itself to subsequent development. The art of the bowyer continued into the 20th century, suspending many automobiles and more than a few motorcycles. The advent of composite materials introduced lightweight leaf springs capable of millions of cycles with no degradation or fatigue and replaced heavier steel for performance applications. The bow remains a simple effective spring by any engineering standard and is inherently balanced from tip to tip.
As an added benefit of a multi-link-type front suspension, front wheel trajectories can be altered by varying length and placement of the connecting links. This trail value fine tuning has the advantage of altering trail values for any given suspension setting. Expressed as a graph, more or less trail can be achieved for any given suspension compression value, as desired, without the constraints of a linear telescoping front fork. The graph may therefore yield an initial scrub-off of trail within the first inch of suspension travel and then a leveling of trail value through the remaining travel. The “feel” of maneuverability with reduced trail will be maintained without the drawbacks.
With a primary resistance force centrally mounted, dampers can follow and are centrally mounted on the chassis tangential to the leaf spring.
More than a design exercise, the four suspension members (girder blades) have commonality and multifunctional capability. Each blade is bilaterally symmetrical so that not only are port and starboard units identical, fore and aft are as well. This design symmetry leads to engineering challenges, but ultimately achieve visual balance and universality within a very specific, proprietary role rather than an adaptation of outsourced parts.
With reverence for the work of such suspension pioneers as Phil Erving, Tony Foale, Perluigi Marconi, Ascanio Rodorigo, Norman Hossak, James Parker and of course John Britten, the suspension of the Bienville Commission seeks the depth of understanding of the giants upon whose shoulders we stand.
On a bicycle, human interface is restricted to grips, seat and pedals. Any further contact such as shins, thighs, calves and ankles would result in friction and would impair the act of pedaling. Obviously a motorcycle "pedals itself," but the origin of the species is exactly that: a bicycle with a little motor that helps to propel it.
The question, “What would a car designed for dogs look like?” is an amusing exercise, in the same way the question, “What would a motorcycle (rather than a self propelled bicycle) designed for humans look like?”
In this case, friction and contact points between man and motorcycle are not necessarily bad. As any experienced rider will tell you, steering inputs come not just from the handlebars and body position, but frequently feed into the motorcycle through a gas tank between the knees. Countersteering forces are applied to the chassis through the hand grip opposite the directional change, but are leveraged by friction from the seat and foot pegs as well.
Part of the magical experience of riding a motorcycle is that somehow, we humans do this intuitively. Perhaps it is part of a genetic knowledge that is formed from the intersection of brachiation and bipedalism that our species inhabits. Perhaps other species posses this intuition as well. Regardless, it takes very little brain power for a human to master the complicated physics of the counter-steer.
Oddly, very few motorcycle manufacturers take the study of ergonomics to a logical “designed for humans” conclusion. When knee-gripping a modern sport motorcycle we come in contact with a wide variety of textures and unreconciled materials. On a single motorcycle you might encounter vinyl on the seat, painted plastic on bodywork, aluminum on the chassis, and painted steel on the gas tank, with huge gaps between each transition. And that's just in the seating area! Suspicion of a form-over-function ethos arise.
Perhaps the resulting "strange forms" the machine would take would render it “too weird” and be rejected by consumers. Perhaps that's why it's not explored by stylists in the first place. But what if a sportscar had lawnchairs for seats? Motorcycles with bicycle ergonomics are not such a far cry from this ridiculous proposition. Conservative styling is reinforced with rigorous stereotypes stemming from the dawn of two-wheeled motoring and what is considered the norm for beauty. A seat must look like a seat, a frame like a frame, etc.
The biggest factor in this perpetuation could be that motorcycles are sold primarily based on looks, specifically the way they look on a showroom floor without a person astride. Who ever heard of a motorcycle showroom with a mirror so that you can look at yourself while you “try it on”? A silly thought, but the observation that, ironically, motorcycles are sold while standing still is valid.
What of that other self-pedaling bicycle: the horse? Development of the interface between man and animal -- the saddle -- has been taking place for the last 2,700 years! Interestingly, saddles not only provide for a more comfortable perch on a horse, they also promote communication from rider to animal. As anyone who has seen a calf-roping contest can attest, horses are not steered solely by reigns in hands.
There is an obvious corollary: the horse-motorcycle, saddle-seat and over two-thousand years of previous development from which to draw inspiration and understanding. The “saddle” of the Bienville Legacy, just as the saddle of a horse, will encourage the free exchange of information from man to machine and back again, while still providing room for athleticism (rider movement).
The thought then, is that the machine is incomplete until the human element is “snapped” into place. Even the most expensive bespoke suit is nothing but a pile of cloth until it is worn, and like that suit, each saddle will be custom tailored for the individual owner. Whilst a perplexing object to behold on the side-stand, once in motion with a person astride, the visual incongruence will be resolved.
Material selection in the modern age presents a bewildering assortment of metals and processes. Matching the functional requirements of a specific part to the properties of a specific alloy requires equal effort in research and colloquial inquiry. The fairly recent accessibility to aerospace-grade materials on the commercial market have opened new doors, specifically the proliferation of titanium and titanium alloys, high-strength steels, carbon composites... and, lest we forget that magical standard, aluminum.
For casting components, 1100 (or pure aluminum) yields soft parts that can be easily finished and with the addition of 3000 series more and more strength can be added. 1100 is also easily spun, and if left un-annealed, is inherently work-hardened. Bolting together work-hardened spun aluminum is an excellent solution for fenders. The 3000 series of alloyed aluminum possesses higher strength, and excellent weld-ability with good wetting action. The tailored saddle platform will be made from 3002 aluminum manganese alloy, hand formed and heliarc welded with 4043 filler rod. For the eccentric housings, a 6000 series is more appropriate. 6061 alloy with a T6 (solutionized and artificially aged) heat treatment gives excellent machinability and strength for complex parts.
Titanium selection for the project will be of two grades. Grade 2cp (commercially pure) and Grade 5 (Ti6Al4V). Grade 2 titanium is the most commonly available of the un-alloyed and its oxygen content gives it good ductility and high tensile strength. It is an excellent all-round material for brackets and suspension components, especially when water-jet cut and bolted together to avoid welding and the associated embrittlement. Grade 5 titanium is alloyed with aluminum and vanadium and is the strongest readily available alloy. It is an excellent choice for axles, suspension pushrods, and fasteners. The weakness of titanium is its poor weldability (extreme sensitivity to ambient oxygen) and difficulty in machining (tendency to gall and spring-back). But, the benefits of a high strength-to-weight ratio and resistance to corrosion make it an excellent (if expensive) choice for structural pieces.
No material available today has the versatility and economy of modern steel alloys. The chromoly (chromium molybdenum alloy) series of steels have the best strength-to-weight ratio for chassis construction. Frame tubes of 4130 all for thinner walls (therefore lighter) than a comparable 1020 carbon steel tube and have the same stiffness. Even so, it can also be welded to 1020 with either an ER70 S-6 or ER70 S-2 filler rod, without a stress relief post-welding process. With a lower malleability than carbon steels, stress fracturing can occur. But the benefits of weldability and strength outweigh (reverse pun intended) the drawbacks.
The term "carbon composite" or carbonfiber most often refers to a cloth made of carbon fibers bound with a polymer (usually an epoxy). The expense of this material lies in the process, not the component pieces. Hand labor is required for laying the fabric into a mold. The three most common methods are wet lay-up, resin transfer molding, and pre-peg. Wet lay-up does not use an autoclave, merely an epoxy that is brushed onto a dry carbon fabric and allowed to harden in open air. Resin transfer implies the injection of a resin (epoxy) into ports in the two-part, all-encasing mold on one end where a vacuum is applied to the other end to draw the resin into the fabric. The ports are then sealed and the entire assembly autoclaved. The pre-peg technique uses fabric laced with epoxy that is activated once laid into a mold, vacuum bagged and autoclaved. This is the most common and perhaps desirable method because of the consistent results in epoxy propagation. The super light and stiff properties of carbon composites are well suited to suspension pieces, provided there is adequate surface area. The structural surfaces of the girder blades are shaped so as to yield high surface area and provisions made to both bond, and mechanically attach interface points for eccentric housings and axle spools. Again, it is an expensive proposition, but when one holds a composite piece, in awe of its light weight, and considers its load bearing capability, justification is easy.
When considering the ultimate motorcycle, surely these materials are at the forefront of thought. Only the accounting department would prohibit their use in the search for the lightest, fastest motorcycle.
Testing Ourselves on the Field of Battle
“How fast is it?” The eternal, simple question. The first question asked by a youngster in awe of an exotic machine, the last question answered by a competitor at Bonneville. Since 1914 the dry bed of a Pleistocene lake in North West Utah has been where Americans have tested the speed of their creations.
The attraction of this most hallowed ground lies in the root of the American psyche. Landspeed racing conducted on asphalt has better traction characteristics, consistency, and weather is not the huge factor that it is on the Salt. But what of racing on the earth, on a natural rather than man made surface? Perhaps, because it is so difficult, the desire to be a part of its history is all the more compelling.
The Bienville project must withstand this test in order to validate its design direction and add objectivity to its construction philosophy. This will separate us from so many “custom” motorcycle projects. Many will find the overall gestalt of this machine challenging, but critique of the styling is best silenced by actual achievement.
Doing things the hard way in order to honor this tradition is tantalizingly close to religion, and inasmuch as a person can have an actual spiritual experience, it seems that Bonneville is all too often described in those terms.
It is, after all, referred to as a “proving ground”, and no humanity can be held to higher standards than to “prove” one's worth in a dangerous pursuit of no real consequence.