Dirt & Street Bikes
As a long-time rider of both dirt and street motorcycles, I have long been the beneficiary of technological leaps in both camps. In the late-1960s, dirt bikes discovered that lighter is, in fact, better.
The World Championship Suzukis of Roger DeCoster and Joel Robert were dozens of pounds lighter than the competition from European marques. To this day, the focus on weight is critical, as it impacts everything that happens on the motorcycle.
Street bikes contributed disc brakes to two-wheels in the ’60s-led by the Honda CB750-but off-roaders did not grab a hold of this superior stopping technology until the early-’80s. By the time discs were added to dirt bikes, the breakthroughs of linkage single-shock suspension and liquid cooling arrived off-road.
I fondly recall my 1981 Yamaha Seca 550 and its nemesis, the Kawasaki GPz550-they were both twin-shocked at a time when conventional wisdom insisted that rising-rate rear suspension was unsuitable for street riding, due to the supposed inconsistency of the travel.
At the time, I suspected that I was hearing an excuse based on lack of R&D, and I was right. These days, virtually every high-performance street bike has rising rate linkage.
Liquid cooling was rare on street bikes in the 1970s, but Yamaha got the water flowing off-road with the 1981 YZ125. However, the YZ did have the odd features of a triple-clamp mounted radiator and coolant directed through the steering head pipe and frame-a quickly abandoned idea. With the exception of a few two-strokes, mainstream street bikes did not start relying on liquid cooling until 1985.
In the mid-’80s, aluminum perimeter frames debuted on street bikes. It was not until the 1997 Honda CR250R that this development made it to mass-production dirt bikes (though my 1990 Beta Zero trials bike had a fuel-carrying aluminum perimeter frame). To make up for it, dirt bikes introduced inverted forks to the motorcycle world.
And, of course, the ebb-and-flow of technology leadership continues. Electronic fuel injection is the latest, greatest thing on motocrossers, and we impatiently await the first mainstream enduro bike with EFI-the 2010 Suzuki RMX450Z.
While it made sense that street bikes-with extensive electronic systems already in place-accessed EFI first, it is interesting that battery-free motocrossers were fitted with EFI systems before their battery-equipped enduro cousins. Regardless, exorcising jetting demons from a carburetor is an exercise I will never miss.
Fly-by-wire throttles and meaningfully adjustable power delivery are two more features I eagerly anticipate on mass-production off-road bikes. Can you imagine having the ability, with the push of your thumb, to turn your trail bike into a torquer for technical single track and a screamer on dirt roads and open trails?
For a current example of a crossover technology moving from dirt-to-street, look no further than the ’10 Honda VFR1200F. Honda’s latest high-tech sport bike takes its valve train design from the Honda CRF-R motocrossers. The Unicam head has the cam operating directly on the intake valves, and on the exhaust valves via rocker arms.
This allows for a smaller, lighter head with only a slightly lowered maximum rev ceiling-something that is not an issue with anything less than the ultimate in high-rpm engines. Perhaps the favor will be returned, and the magical automatic transmission in the VFR1200F will be adapted for off-road use.
All this, of course, leads to one inescapable conclusion. If we are street riders, we are dependent upon dirt bikes for some of the improvements we take for granted, and vice-versa.
When motorcycles come under fire from the bureaucracy-be it a concern for too-fast sport bikes, annoyance at boisterous cruisers, or intolerant users of public lands who cannot accept motorcyclists as part of the public-we have to stick together.
Brothers in arms, let us keep our sport on two-wheels and rolling boldly into an ever-improving future.Google+