Here was an extremely enjoyable dual-purpose big single, a trail bike, with reasonable suspension and good manners. And a honkin’ great 500cc engine, knocking out more than 35 horses at 6,500 rpm, pushing about 300-plus pounds down the pavement or over the dirt road on the mountain. This was a great way to explore the backcountry, limited only by a gas tank that held 21/3 gallons. But that was a safe hundred miles, as consumption was upwards of 50 mpg.
This playbike was a product of Paris-Dakar fever. The motorcycle classes in the first two P-D races in 1979 and 1980 were won on a much-modified Yamaha XT500, and wannabe racers wanted those big four-stroke singles.
The origins of the Suzuki thumper go back to 1978 when the SP370 came out, the company’s first big four-stroke single—having seen the inevitable demise of street-legal two-strokes. The 370 had a bore of 85mm, stroke of 65.2mm. This model was well received editorially, but not a success, suffering too much weight and too little power. One has to admire the Hamamatsu folk for persevering. A companion to the SP was the DR enduro version, with slightly less weight and longer suspension travel; suitable for those wishing for more off-road use. Two years later, in 1980, the SP/DR400 appeared, with the bore enlarged by 3mm to 88mm, or 397cc. The 400 was only a one-year model.
For 1981 there was an entirely new engine, the single remnant of the old being the bore staying at 88mm, with the stroke now growing to 82mm for a grand total of 498cc. A pair of counterbalancers was added to the crankshaft, one fore, one aft, as vibration did become an issue with the half-liter size. This air-cooled, wet-sump engine had a chain-driven single overhead camshaft, four valves and a heftyish compression ratio of 8.7 to 1. Fuel was inducted into Suzuki’s much-boasted about TSCC (Twin Swirl Combustion Chamber) via a Mikuni 40mm CV carburetor, and the spark was provided by a capacitive discharge ignition, using a magneto on the flywheel. A 6-volt electrical system with a very small 4 amp-hour battery kept the bike street-legal with turn signals and brake light.
The starting mechanism was old-fashioned, by foot, but if one adhered to the proper drill a determined kick on the starter usually fired the SP right up. A new-fangled compression release system made the job a little easier: pull the lever in, let go, both exhaust valves are open, and as the rider eases the kickstart just past top dead center, the release would close the valves on its own, followed by the kick. Even cold it generally worked.
Helical gears ran the power to the wet clutch, through the five straight-cut gears in the transmission, with a #520 chain driving the rear wheel.
The engine/transmission unit was bolted into a steel cradle frame, with a single downtube splitting just in front of the crankcase, going under and cradling the engine. From the steering head a straight tube went rearward under the tank, then split. A box-section steel swingarm pivoted off the frame using needle bearings. The twin-shock rear suspension had adjustable spring preload and compression damping, and allowed for 7.7 inches of travel. The rear wheel had a diameter of 18 inches, with a fat 4.60 semi-knobby grabbing the dirt, and a full floating 6-inch drum brake.
The telescopic fork up front used air (adjustable) and oil to control the ride, and also provided 7.7 inches of movement, quite enough for some seriously bouncy work. A 21-inch wheel with a 3.00 tire provided accurate steering in the rough spots, and another 6-inch drum brake was very useful on the pavement but required moderation in the dirt. A reasonably sized skid plate protected the sump. The exhaust pipe went up high on the left side, and was protected in case of a fall. Of which there would probably be many.
A leading axle and 29.5-degree angle on the fork gave the SP a 57.5-inch wheelbase. This made for quick turns in the dirt, but not much stability at 100 mph—fortunately top speed was not more than 90 mph. Overall weight with a full tank of gas ran 325 pounds, not bad for a dual-purpose bike, though it was 20 pounds more than the companion DR that lacked turn signals and other street-legal paraphernalia.
A long, flat saddle was good for sliding around on, although the 34-inch height was a tad tall for some. A pair of traditional round instruments gave road speed and engine speed.
The only ad Suzuki seemed to have for the model was: Think of it as a two-wheeled jeep. With the SP in front of a jeep out in the countryside. Very nice. Though nobody seemed to know what the two letters stood for.
A 278-page service manual for both the SP and DR was quite useful, with detailed instructions on engine removal, followed by sections on disassembly of the upper and bottom bits, inspection and reassembly. Though with the crankshaft running on seven ball bearings, it was doubtful much would go wrong with the lower end.
For 1984, the engine was enlarged to 589cc—and the SP version was dropped, leaving only the newly street-legalized DR600—which had monoshock rear suspension and a useful 5.5-gallon gas tank. This eventually grew to be the 779cc DR800, more popularly known as DR BIG, with a 29-liter tank. But that is another story.
UPDATE: According to Suzuki’s official Identification Guide 1970-1990, the SP500 and DR500 both ended in 1983, and then the SP600 appeared in 1985 as a one-year model, after which the SP designation vanished.