Retrospective: Honda GB500 Tourist Trophy: 1989-1990
June 22, 2007
Filed under Honda Motorcycle Road Tests: Reviews on Honda Motorcycles, Retro + Vintage Motorcycle Reviews
(This Retrospective article was printed in the June 2007 issue of Rider.)
STORY and photography BY CLEMENT SALVADORI
This really was a superbly entertaining machine, tremendous fun to ride, but one which could not find its niche in the American motorcycling world.
All too common thinking was that street bikes needed a minimum of two cylinders, if not four, and while a big single was OK for the dirt, it was not considered worthy of the road.
How soon we forget! Thirty years before, the Brits were having a great time selling 500cc BSA Gold Stars and Velocette Venoms, although the American public was much more attuned to the 650cc vertical twins that proliferated. The thumper, the big single, was a sophisticate’s choice, a bike that the experienced rider could take through the twisties at a greater rate than the bigger twins.
In 1987 Soichiro Honda was still exhorting his minions to come up with new product, even though the motorcycle market had been stagnant for a while—especially in the United States. For all we know, this might have been Mr. Honda’s own notion, as he had a great respect for the once-great British motorcycle industry.
The GB500 was as much a styling exercise as anything else, made to look like a machine one might have seen on the Isle of Man during TT race week. The official name of the motorcycle was “Tourist Trophy,” spelled out with decals on both side covers. Which, by its very name, was a race open to all touring visitors, harking back to the early days of the TT. The gas tank, the solo saddle, the clip-on handlebars, even the faux-megaphone muffler—all served to give it a very English air.
Of course, there were notable differences between the venerable Brits and the new-fangled Honda. The biggest was in the cylinder head, where the Gold Star/Venoms were running two overhead valves operated by pushrods, while the GB had a chain-driven overhead camshaft that depressed the four valves in the Radial Four Valve Cylinder (RFVC) head, which also had a genuinely hemispherical combustion chamber. Since the valve stems were not parallel, this meant that Honda had to make complicated double-jointed rocker arms in order to operate each pair… which never gave a problem.
The Brits like cylinders with roughly equal dimensions, the Gold Star having an 85mm bore and 88mm stroke, the Venom a perfectly square 86/86, while the Honda ran a short-stroke, oversquare cylinder with a 92mm bore, 75mm stroke. Part of that was due to the fact that the GB’s engine was derived from the 1983 XR500, a dirt bike that enjoyed a bit of torque. The XR version ran a pair of 28mm carbs, whereas the GB500 had one big 42mm round-slide Keihin.
In terms of horsepower the Brits liked to claim upward of 40 ponies, depending on the state of tune. The Gold Star, for example, offered various exhaust systems, camshafts, carburetors and compression ratios, from a 6.5:1 compression ratio for the touring model, up to 13:1 for racing; a reliable street version of a sporty OHV 500 was probably putting out some 30 horsepower at 6,200-6,500 rpm. Thirty years later the GB500 measured on the dynamometer a reliable 33 horses at 7,000 rpm.
But don’t knock that. A lot of riders know it is more fun to go fast on a less powerful bike, and to embarrass the 100-horsepower 600s on a curvy road. The GB used straight-cut gears for the primary drive, a wet clutch, five gears in the transmission and chain final drive. The powertrain sat in a full cradle frame made of steel tubing, with a squared-off steel swingarm. The engine was of the dry-sump variety, as were the Brits’.
The suspension was not much more sophisticated than that found in 1959, with a pair of preload-adjustable Showa shocks, the modern equivalent of the old British Girlings, and a non-adjustable fork with hydraulic damping. In keeping with its nostalgic sense the GB ran spoked 18-inch wheels and tube-type tires, though the Brits were running 19-inch wheels back then. However, those new Bridgestones were generations better than the Dunlop K70s of yore; Dunlop makes great tires nowadays, but the rubber compounds back then were less than grippy, especially in the wet.
The most noticeable advantage of the GB was the disc brake on the front wheel, with a twin-piston caliper, as opposed to the single-leading-shoe drums on the Gold Star and Venom. The GB ran a drum on the back, which is more than adequate as most of the effective braking comes from the front.
The wheelbase of the GB, with 30 degrees of fork rake, was a tight 55.6 inches, ensuring its ability to get around corners fast. The Brits were even tighter, running at 54 inches. The GB, with four gallons of fuel in the tank, weighed in at 390 pounds, much the same as its predecessors.
However, the Honda weight included an electric starter; pull out the choke, turn on the ignition, push the button, and the engine was lit. Yes, there was a kickstarter on the GB, but that was more for poseur purposes than being anything practical, as it needed to be in alignment, if not with the stars then with the capacitor ignition, which occurred only once every few kicks. The old Brit bikes required an entire drill: Turn on the petcock, fiddle with the handlebar controls to retard the magneto, tickle the carb, pull in the compression release, get that piston just past top dead center, then rise way up and deliver a hefty whack to the kickstarter. If the gods were smiling on you, the engine might fire right away, but usually the drill had to be repeated a number of times. That button was a very good addition!
Despite the immense improvements in lubrication systems, a kind rider would let the GB’s engine warm for a minute, snick the lever into first gear and ride away. Dawdlers could keep the engine poking along at any rpm, but the sporters would keep the revs above 5,000. The GB was best ridden on curvy back roads, far away from any freeway. One thing that the GB did lack was an appropriate exhaust note. The old thumpers had a sharp bark when they were on the gas, but Honda was adhering to legal decibel levels. The Gold Stars were famous for their backing-off twitter, while the Venom enjoyed a notorious boom when running over 5,000 rpm.
The GB500 was a really exhilarating motorcycle to ride. Still is. Since its demise it has become “collectible,” and few come on the market. When they do, the price is high. Though not nearly as high as that of a Gold Star.