Mr. Soichiro Honda was fond of saying, “More is learned from failure than from success.” When you have a success, you go to the party. When you have a failure, you stay up all night trying to figure out what you did wrong. There was a period in English motorcycling when experts announced that best handling could only result from designs having constant wheelbase. Based on this, the telescopic fork was rejected because it lets the front wheel move back as it compresses, shortening the wheelbase. The best suspension, therefore, was a leading or trailing link fork, with its travel restricted so its motion was mostly vertical. Hmm, how can we get constant wheelbase at the rear? I know! We’ll invent sliding pillar, in which the rear axle judders up and down on short sliders, moving on vertical pieces of pipe on either side. The obvious and simple pivoted swingarm was rejected because of its wheelbase change. Meanwhile, with the rear wheel moving straight up and down on its pillars, the drive-chain became tight at top and bottom positions. Now reality intervened in the form of the 1950 Manx Norton, with a telescopic fork up front and a swingarm at the rear. Its excellent performance in the hands of the late Geoff Duke blew over the four-cylinder Gileras and it could accelerate past sliding-pillar Manxes on the outside of turns. Back to the drawing-board for constant wheelbase. Earles forks and short leading links had their brief vogue (BMW, Guzzi) in the mid-to-late 1950s, but where are they today? Ride one of those classic BMWs through a long fast turn and thrill to the pendulum-like swing of all that steered mass, located far behind the steering axis. Wise men now came up with one that has been rediscovered by inventors about 50 times since then, namely, to achieve perfectly constant rear chain center distance by pivoting the swingarm on the same axis as the gearbox sprocket. This looks really attractive on paper, but when you build a powerful motorcycle this way, it squats down under power in corners and pushes the front, running wide. Hmm, closer study reveals that successful designs locate the swingarm pivot higher than this, using chain tension to generate a lift force that neutralizes acceleration squat, stopping front-end push. The next doctrine was that the soul of good handling is a low center of gravity. I tried this one on myself for a while and then had to give it up when I saw tall bikes winning all the races. Nothing succeeds like success! What was going on? Even Honda were taken in by this wisdom of the ancients, which caused them to build their 1984 NSR500 with its gas tank slung under the engine and its pipes routed over its top. It was notably slower in direction-changing than the previous 1983 NS3 triple, which had its gas tank on top. Then it turns out that when a motorcycle rolls over for a turn, it doesn’t roll around a line through its tire footprints. It rolls around its own center–of-mass, which is about 20 to 22 inches above ground level. That in turn means that for quickest direction-changing, large masses such as engine and fuel should be close to that height. Putting the fuel on the bottom moved its mass away from the center, making the bike slower in roll. Point taken! All the manufacturers invested in special purpose machines to actually measure polar moments, and gas-on-the-bottom was discredited. The constant wheelbase idea is still out there, causing periodic eruptions such as the Chebyshev linkage. Like Kawasaki’s twin swingarm “Fu-bar” suspension of 1974, the Chebyshev has two swingarms joined at their rear extremities by vertical links. But unlike Fu-bar, whose arms are nearly parallel, the Cheb’s arms cross each other before attaching to the vertical links, giving a more constant vertical axle motion (the axle passing through the centers of the two vertical links) and bringing back that sterling quality of sliding pillar, a chain that tightens at top and bottom of its motion, yet is loose in the middle. The Fu-bar taught us the treasured lesson that two weak swingarms are stiffer than one (look at the mighty arms on sportbikes today!), and the Chebyshev reminded us that simplicity was the original basis of the motorcycle’s appeal. Turbochargers hit the automotive world with a soft hiss of impeller noise and a screech of spinning tire rubber. Not bad! You mean this little 15-pound lump of cast-iron, aluminum, and Inconel 713 can really double the power of my small-block? Soon the prefix “turbo” became an advertising synonym for ‘super’. The motorcycle industry took its turn at bat in the turbo game but it was a no-hitter. Turbos look simple but the power they make arrives with such a rush, often after a perplexing delay, that motorcycles have to be straight-up-and-down to risk it. Maybe some miracle of electronic intervention (with ten levels!) can yet make turbos a part of sports motorcycling, but like fusion power, that lies in an indefinite future. Over and again for more than 60 years, motorcycle sociologists have concluded that bikes would find a vast number of new buyers if only they could be made quiet, clean, inoffensive, and….well, more like…cars. Vincent and Sunbeam bought into this “carcycle theory” in the late 1940s, producing the ‘Black Prince’, totally enrobed in squeaking fiberglass panels, and the fat-tired S7. Later came Velocette’s marvelously underpowered ‘LE’, and in our own era we have seen the carcycle concept vigorously reprised by Honda’s Black Prince-emulating ‘Pacific Coast’ and the quirky NC700X maxi-scooter. They say “Don’t muddy the water–you may have to drink it soon.” In the coming era we are promised zero traffic accidents thanks to autonomous vehicles. If motorcycles aren’t then banned outright, how will they work? When the occupant of an autonomous motorcycle has nothing to do, what will keep him or her from falling off as a result of going to sleep? Doors? Seat belts? A styro-pod? Won’t the autonomous motorcycle require retractable training-wheels to keep it upright as the “cycle complete” ring-tone tinkles at the destination? Two main wheels plus two training wheels equal four, so evolution will be complete; the carcycle triumphs at last.By Cycle World
