My, How the Racing Motorcycle Has Changed—By Kevin Cameron

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Wes Cooley

Wes Cooley, Daytona International Speedway, 1981

It’s interesting to consider just what it is that makes motorcycles fast in a given era. In our own time, we can see that tires have reached a high level of both grip and durability. In racing, it is no longer unusual for a rider to set the fastest lap of the race two laps from the end. Thirty years ago, wide bias-ply tires used in 500cc Grand Prix racing were so short-lived that they were being brought to the starting line without even being scuffed. Even at the end of that era, five-time 500cc World Champion Mick Doohan would say that a rider with a 10-second lead on lap 15 would “spend the last 10 laps sliding around” because of tire deterioration.

Tire and rim sizes have grown at the same time. A 1978 1025cc Superbike rolled on 2.5-inch front and 3.5-inch rear rims—sizes that were being used by 125cc GP bikes in 2009.

Another great strength of the present is the smooth power given by the new breed of four-stroke engines with electronic fuel injection and mapped ignition timing. The power of 500cc two-strokes came in with a bang despite devices such as exhaust gates, forcing riders to get their turning done early, then lift the bike up onto a wider part of its tires before turning the throttle to accelerate. Attempting to “feed power” as modern four-stroke riders can do ended either in a sudden slide as too much power hit or in an actual highside.

Not all the advantages, however, are with modern bikes. Acceleration is thrust, divided by weight, so light bikes like the middle-period 500cc two-strokes could accelerate really fast even though they developed “only” 150 horsepower. Before the 130-kilogram weight minimum (286 pounds), a few 500s weighed less than 250 pounds. That, plus a 170-pound rider and 30 pounds of fuel added up to 450 pounds, or about 3 pounds per horsepower. Today’s Superbikes are about 100 pounds heavier, giving a 205-horsepower bike 2.75 pounds/horsepower—not all that much more. Of course, MotoGP four-strokes, with a bit more power, look even better.

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Freddie Spencer

Freddie Spencer, Laguna Seca, 1980

Let’s shift gears a bit and compare then-and-now Superbikes. The earliest days of AMA Superbike were the late 1970s, when machines like Kawasaki and Suzuki 1025cc Fours still had 1950s-style twin-loop frames of curved, welded tubing and not triangulated straight tubing as now employed by Ducati. Those machines were not stiff enough to be stable at their maximum speeds, which is why so many early AMA Superbike events were won by European machines, Moto Guzzis and Ducats, which were less powerful but more stable.

By the late 1980s, some makers were beginning to switch their sportbikes to much stiffer and lighter twin-beam aluminum chassis like those in 500cc GP. Production of such chassis was expensive and slow because pressed-aluminum beams had to be welded to complex castings supporting steering head and swingarm. Today, improved casting methods allow entire chassis to be welded from just five sections. Because casting allows good control of wall thickness, such cast chassis now combine excellent stiffness with reasonably light weight.

The Kawasaki 1025cc Superbike that won early 1980s races in the U.S. produced 150 hp at 10,250 rpm, and it was working very hard at that level. A separate cylinder and crankcase rubbed together as the 31-pound, pressed-together roller crankshaft writhed violently. One result was base-gasket leakage and another was cracking of major parts.

Today’s liter-bike engine has its cylinder and upper crankcase cast in one rigid, self-bracing unit. A forged one-piece steel crank runs on Formula One-style plain-journal bearings. Because bores have grown and stroke has shortened, such engines now rev reliably to 13,000 or even 14,000 rpm, enabling them to make 30 percent more power than their “forefathers” of three decades ago. Four valves per cylinder are easier to control at high revs than were the two larger, heavier valves of earlier engines.

Brakes are another important area of advance. “Mr. Superbike,” Rob Muzzy, had to adopt extraordinary measures to give his 1981-82 1025cc Kawasakis good brakes. Starting with a cast-iron blank almost an inch thick, they ground it flat, then stress-relieved it, again and again, to produce at great cost a disc that did not warp beyond usefulness in a single event. Today, the necessary material specification and production process have been mastered, and race-quality iron Superbike brake discs are only a phone call away. Be prepared to undertake a certain degree of expense, of course!

Today’s ceramic-metallic friction material is also a big improvement over the organics of yesteryear, which gave less friction overall and were adversely affected by wet conditions.

Another area of change is forks, whose stiffness and damping sophistication have increased vastly. Early Superbikes had 36mm fork tubes of the “right-side-up” variety, but all of today’s sportbikes have forks whose larger-diameter upper members are clamped in the fork crowns. The lower male sliders are today a minimum of 42mm diameter and some are as large as 48 or even 50mm. Legend recalls that Gary Nixon once permanently bent a set of 36mm conventional fork tubes by just braking hard.

Despite such changes, there are riders who are still thrilled by the rough-and-ready sit-up style of long-ago Superbikes. This looks “right” to them. Such people point out that today’s bikes all look alike; from the spectator stands, a stocker, a MotoGP bike and a World Superbike all look pretty much the same. This, in part, accounts for the continued popularity of “naked” bikes, which honor the older style.