Technologies That Revolutionized Modern Motorcycling, Chapter 3

[Hugh Janus]

The first big-bore Japanese models were heavy on power but still relied on old-school chassis concepts. (Motorcyclist Archives/)

Even though the handling, chassis, suspension, and tire revolutions in motorcycling had already begun by the early ’70s, the first Japanese big bikes (designed by engineers trained in the 1950s and ’60s) were little affected by them. That meant they were still based on 1960s' chassis and suspension concepts.

Famous protagonists of early ’80s Superbike races included Eddie Lawson on his Kawasaki juggernaut. That’s Freddie Spencer on his tail. (Motorcyclist Archives/)

1975: US Superbike Racing Begins

Inevitably, people tried to race them. The concept of Superbike racing traces back to the AMA production classes of the early ’70s, which were expanded to include the new behemoths. In racing form, they wobbled, they weaved, their brake discs coned, and pistons and rods broke. It is interesting to review paddock photos from that time, which show rapid, race-by-race evolution, as builders reinforced chassis and hot-rodded engines. Recognizing that traditional swingarms of the day—mostly just three pieces of pipe welded together—were too flexible for use with race tire grip, the AMA ruled that “Swingarms may be modified or replaced.” Instantly, swingarms on racebikes became strongly braced by added structure.

Related: Honda CB750 - CLASSICS REMEMBERED

It was a time of “go or blow,” when Hideo “Pops” Yoshimura—in legendary fashion—cranked in an optimistic 45 degrees of spark lead with 12-to-1 compression and hoped for the best. Many an early Superbike failed to finish. Slowly, a consensus of what did and did not work emerged, and the fast learners prevailed. As always, trying to make racers out of mass-produced streetbikes was a tall order.

The Japanese fours always had winning power, but at first they couldn’t use it because their flexing chassis began to weave threateningly long before top speed could be reached. That allowed remarkable early Superbike wins by lower-powered but better-handling European makes such as BMW, Guzzi, and Ducati. Weave had been a problem in pro racing too.

Chassis Have To Adapt

By the 1980s a trend emerged in racing—chassis structure under the engine was atrophying away, while the bracing of the steering-head above and ahead of the engine was being made stronger. Fast-improving tires are also always a problem for existing chassis technology, as long-serving Harley-Davidson race manager Dick O’Brien told me in the summer of 1969: “About the time we get the goddamned chassis settled, along comes Goodyear with more f—g grip, and we’re back in the s—t and have to do it all over again.” Some 20 years later, Erv Kanemoto, then working with Honda’s NSR500, would say something very similar: “The thing the teams fear most is that the factory will come with a new chassis, because then we’ll have to spend the next six months getting it to handle as well as the old one.” And in our own era, when Bridgestone ceased to be MotoGP’s spec tire supplier at the end of 2015, new tires from Michelin took the teams and their riders two years' hard work to develop successful setups and appropriate riding techniques.

Related: As the US Market Exploded, Japan Took Over

Fans loved late ’70s Superbike, both because the bikes resembled those owned and ridden by spectators and because of the riveting drama of upright heroes sliding and wobbling around the circuits. This popularity made it essential for manufacturers to win these events. While fabricators strove with torch and rod to brace “chatter-flex” street chassis for racing, suspension people were ringing the changes in fresh fork and shock technology. Solutions improved by the minute, and fast learning was the key to success. And the message was getting back to Japan: Something better is needed.

Honda’s Interceptor 750 Superbike. (Honda/)

More Capable Production Bikes Hit The Market

This steered Japanese design in a fresh direction. Future Superbike races would be won, not by warmed-over 500-pound street putts, but by a new class of designs that were thinly disguised racers in mass-produced form. The first of these was Honda’s Interceptor 750 Superbike of 1983. Always bear in mind that advanced production systems, by reducing unit cost, allow high-tech features to be made affordable. This shift all but eliminated broken con-rods, blooched crankcases, warped brakes, weaving chassis, and “joke” swingarms.

If you look at photos of racebikes of the 1950s, you’ll see that riders are far back, reaching a long way to the bars. When tucked in, their faces were on the tank. At the time, this was believed to “increase rear tire traction.” But as rising power turned bikes into dragsters with some limited turning ability, riders and engines had to be moved forward to keep the front wheel on the ground and steering. Tucking in on a modern sportbike or racer plants your face on the top steering crown, not on the tank behind it. Riders have moved forward 6 to 8 inches, and engine mass is now concentrated as far forward as it can go.

The Coming Of Electronic Ignition

Beginning in 1969, the chronic ignition problems in racing had been addressed by various forms of electronic spark generators, free of the rapid wear and timing scatter of mechanical contact breakers (“points,” in the language of the time). If, in 1967, I set the timing on my TD1-B’s Hitachi MF2RY magneto and then rode a practice, upon checking timing again, I’d find it out of time (the points cam was way out on one end of the crankshaft). In Spain, Femsa in 1969 produced a very successful “pointless” electronic ignition for singles and twins, and in 1970-71 the German Krober, available for singles through fours, also hit the racing market. Yamaha in 1969 brought two types of non-contact ignition triggers to Daytona for its team bikes—one magnetic, the other based on RF. Points-triggered magnetos had to go because people were losing engines and races to their problems.

Extended Service Intervals

Older riders remember when cars and bikes required regular “tune-ups”—as often as every thousand miles. Engine oil was changed, plugs would be cleaned and re-gapped, points gap set, and ignition timing adjusted. Motorcycles with non-hydraulic tappets would also have their valve clearances checked and reset. The automotive world now set a new goal of extended service intervals, and production motorcycles would follow. It had been common for motorcycle owners to perform much of their own maintenance, but as people from all walks of life bought bikes, fewer new owners had such skills. This turned extended service intervals into an essential marketing tool.

Handling: Americans Decide They Like It

Up to this time, readers of bike mags had flipped straight to the specs page for any new model to read its quarter-mile time and top speed. Industry regarded those numbers as the proven formula for success—little else was important. Imagine the surprise of marketers when Honda’s Interceptor 750 of 1983, designed as a low-production homologation special mainly for US Superbike (the class limit dropped to 750 that year), sold out, with riders begging for more and praising the new model above all for its handling. Handling wasn’t even a concept then, but compared to slow-steering, mile-long literbikes, the Interceptor was something fresh—agile and quick. It made riders feel in command. A simultaneous flood of similarly agile middleweights from the other makers poured forth, including Ninjas and Secas, and then the remarkably lightweight GSX-Rs.

Honda made waves in the 600cc sportbike class and Supersport races in the late 1980s. (Motorcyclist Archives/)

The Novelty Of Raceable Production Bikes—Supersport

This market shift was a gift to street riders and amateur racers alike, resulting in intense club-race action in production classes, strong sales, and contingency money from the importers for race wins. In that contingency-driven time, it was said that Suzuki made back in parts sales every penny it spent on payouts to riders winning races on their GSX-Rs. Very quickly, top pro riders found themselves an integral part of the drive to sell these much-more-capable middleweights. 600 Supersport, conceived as low-cost racing for all, became a hard-fought factory racing class in the mid- to late ’80s and remained so through the ’90s.

Stronger Chassis Become Essential

Manufacturers in GP racing in the later 1970s and ’80s had found that the stiffer they could make chassis, the more quickly bikes recovered from the constant upset of traction loss as tires spun and re-gripped.  Superbikes were four-strokes, but GP racing by 1975 was 100 percent two-stroke (even sidecar). During the 1980s a complete change of chassis technology occurred. Out went even the best of the old tubular steel construction, replaced in most cases by twin large-diameter oval-section aluminum beams. As with axles and fork tubes, this was driven by the rapid increase in the stiffness of tubes with diameter—something like the third or fourth power. So-called “monocoque” single box-beam chassis had been tried (most notably by Kawasaki in its KR500 GP bike of 1980-82) but perhaps because of service accessibility the twin-beam structure won the day. But why aluminum and not steel? Steel, being roughly three times heavier than aluminum and also three times stronger and stiffer, would become so thin if made into beams of similar weight that buckling (like a thin plastic drinking straw) would become its failure mode. Aluminum, with three times the wall thickness for equivalent weight, would remain strongly buckle-resistant.

Kawasaki leveraged its success in Superbike with 1982’s KZ1000R Eddie Lawson Replica. (Motorcyclist Archives/)

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