The Suzuki RG500 Gamma (1985): the Grand Prix bike sold in dealerships

Cult modelsSuzuki 1980sGrand Prix 500

Launched in 1985, the Suzuki RG500 Gamma brought the architecture of the factory machines that had dominated the 500 cc championship onto the road. Its square-four two-stroke , 498.5 cc, with rotary disc valves and a cassette gearbox, claimed 95 hp for 154 to 156 kg dry in an aluminium double-cradle frame. In Grand Prix racing, the RG500 delivered four riders' titles — Barry Sheene in 1976 and 1977, Marco Lucchinelli in 1981, Franco Uncini in 1982 — and seven consecutive manufacturers' crowns. Against the Yamaha RD500LC, it played the featherweight card, until emissions rules wiped it from the catalogues.

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A factory machine with a licence plate

In the mid-1980s, the one-upmanship between Japanese manufacturers reached an unprecedented peak: rather than drawing vague inspiration from racing, they decided to sell the race bike itself. Suzuki introduced, in 1985 , the RG500 Gamma, whose name took up the Greek Γ already carried by the factory machines entered in the 500 cc world championship. That same year, the Hamamatsu firm also launched the GSX-R750, the other thunderclap of that vintage: two radically opposed visions of the sports bike, one four-stroke and usable, the other two-stroke and uncompromising.

The RG500 Gamma is not a styling replica. Its engine architecture, its induction system and its chassis descend in a straight line from the factory RG Γ 500s of the start of the decade. The result is nothing like a marketing exercise: it is probably the road bike most literally derived from a GP machine ever sold by a major manufacturer. An RG400 of 397 cc producing 59 hp was offered alongside it in Japan to fit local licence rules. The brand's story, told in our Suzuki profile, has probably never produced an object so directly born of the track.

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The rotary-valve square four, the centrepiece

The heart of the Gamma is a liquid-cooled 498.5 cc two-stroke four-cylinder, bore and stroke 56 x 50.6 mm. Its so-called “square four” layout places the four cylinders at the four corners of a square, above two crankshafts geared to a central jackshaft that passes the drive on to the clutch. The pistons work in opposed pairs, phased at 180° : mechanical balance is near perfect, to the point that the engine needs no balance shaft at all. The whole thing is stunningly compact: half a litre packed into the bulk of a twin.

Induction is the second bravura piece. The mixture goes straight into the crankcases through rotary disc valves — exactly as on the racing RG500s — fed by four 28 mm flat-slide Mikuni carburettors sitting on the flanks of the engine. To this Suzuki adds its AEC (Automatic Exhaust Control) system: extra chambers placed just ahead of the exhaust ports fill at low revs to lengthen the tuned length of the pipes and swell the torque, then close via a servo motor at high revs to free up the top of the rev range. Enough to give a usable band running from roughly 5,000 to 10,000 rpm — an unhoped-for spread for an engine like this.

Claimed power stands at 95 hp at 9,000 rpm, with 72 Nm of torque at the same revs. Period measurements showed more like around 78 hp at the rear wheel : the gear train takes its tithe. That is less than the roughly 120 hp of the genuine factory engines, but the nature of the unit is identical. The six-speed cassette-type gearbox, pulled out from the clutch side to change the ratios, finishes giving away the racing ancestry. Nothing to do with the rustic brutality of a Kawasaki H2 750 from the previous decade: here, the two-stroke has become a science.

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Aluminium frame, featherweight and thoroughbred behaviour

The chassis follows the same logic. The Gamma sits on an aluminium square-section double-cradle frame, a material still rare on a production bike in 1985, whose cast steering head doubles as an air intake duct feeding the carburettors. Up front, a 38 mm telescopic fork fitted with the Posi Damp anti-dive device; at the rear, Suzuki's own Full Floater suspension and its square-section aluminium swingarm. Braking lines up two 260 mm discs gripped by four-piston calipers, plus a 210 mm rear disc.

The figure that strikes hardest is still the one on the scales: 154 to 156 kg dry depending on the source, a little over 180 kg fully fuelled according to period road tests, with a fuel tank of 22 litres and a wheelbase of 1,425 mm. Set against its 95 hp, the result is ferocious: the press of the day recorded a top speed of around 235 km/h and a standing-start 400 metres in 11.2 seconds. Above all, the Gamma rides like a track machine, with low bars, a tucked-in riding position and instant turn-in — at the price of non-existent comfort and a power delivery that never forgives a lapse in attention. The principles set out in our guide to taking a corner cleanly take on a very concrete value on this sort of mount.

🏍️ To carry the brand's spirit into the garage and the house alike, our Suzuki: accessories and motorcycle decor section has everything you need to fly its colours.

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The Grand Prix RG500: four riders' titles, seven manufacturers' crowns

All the road bike's legitimacy rests on the record of its racing ancestor. Introduced in 1974, the Grand Prix RG500 imposed its rotary-valve square four on the premier class and quickly became the weapon of the private teams as much as of the factory. In 1976, its dominance was such that RG500s monopolised almost the whole top of the world standings.

The count leaves no ambiguity: the RG500 delivered four 500 cc world titles in the riders' standings. Barry Sheene was crowned in 1976 and 1977, then the Italian Marco Lucchinelli in 1981 and his compatriot Franco Uncini in 1982. On top of that come seven consecutive manufacturers' titles between 1976 and 1982, a run few machines can claim. It is precisely the RG Γ that won in 1981 and 1982 that served as the technical reference for the 1985 road bike. Other notable riders raced an RG500 without taking the crown, such as Randy Mamola, several times runner-up in the world championship.

What came next belongs to another architecture: Suzuki dropped the square four for the V4 RGV500 at the end of the 1980s, with which Kevin Schwantz would be crowned in 1993. The brand's full journey in the premier class is retraced in our article on Suzuki in MotoGP.

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The duel with the Yamaha RD500LC

The Gamma did not arrive on virgin ground. Yamaha drew first, as early as 1984, with the RD500LC (RZ500 for export, RZV500R in Japan): a 499 cc 50-degree V4 claiming 88 hp at 9,500 rpm. Two philosophies faced off — the square four at Suzuki, the V at Yamaha — for one and the same goal: putting a 500 Grand Prix bike on the road.

On paper as on track, the Suzuki holds the inside line. It shows more power and, above all, far less weight : the figures published for the Yamaha range from around 180 kg in comparison tests to 196 kg dry for the aluminium-framed Japanese RZV500R and 205 kg for the steel-framed European RD500LC. Next to that, the Gamma looks almost as light as a 250. Comparison tests credit the Suzuki with around 232 km/h against 217 km/h for the Yamaha, and grant it an aluminium frame taken straight from the race bike. The Yamaha, better finished and more civilised, offers in return a distinctly more liveable riding position — a refinement that paradoxically earned it a reputation for being tame. Anyone who had tasted the RD350 LC found in both 500s the same electric surge of power, multiplied by two.

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A lightning-quick disappearance, and a second life among collectors

The reign was short. Launched in 1985, the RG500 Gamma saw its production concentrated over 1985-1987 — the figures usually quoted mention 9,284 RG500s and 6,213 RG400s built —, with the bike staying in the British catalogue until 1989. It was never officially imported into the United States, federal emissions regulations having closed the door on big road-going two-strokes; a handful of examples got there via Canada.

It really was the tightening of emissions standards that killed the breed: the two-stroke, with its burnt oil and part of its fresh charge going straight out of the exhaust, could not keep up without losing what made it interesting. In-house competition did the rest. At the very same moment, the GSX-R750 offered comparable performance with a reliable, economical and clean four-stroke engine: the public made its choice, and the modern sports bike was built on that template, from the Fireblade to today's 1000s.

What remains are a few versions that have become cult objects, first among them the Walter Wolf Replica and its livery lifted from the Formula 1 single-seaters of the Austrian-Canadian magnate. Values have since gone through the roof, and healthy examples — original barrels, un-drilled exhausts — can be counted on your fingers. It remains one of the very few road bikes that can claim, part by part, to come from a Grand Prix machine.

🏁 Fans of faired two-strokes happily keep a trace of them on the shelf: take a look at the miniature motorcycles section.

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Summary table

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FAQ — Frequently asked questions

• What exactly is the engine architecture of the RG500 Gamma?
  It is a liquid-cooled 498.5 cc two-stroke four-cylinder laid out as a square four: four cylinders spread above two crankshafts geared to a jackshaft, with the pistons working in opposed pairs phased at 180°. Induction goes straight into the crankcases through rotary disc valves, fed by four 28 mm Mikuni carburettors.
• How many world titles did the Grand Prix RG500 win?
  Four titles in the 500 cc riders' standings: Barry Sheene in 1976 and 1977, Marco Lucchinelli in 1981 and Franco Uncini in 1982. To these are added seven consecutive manufacturers' titles between 1976 and 1982.
• What power and weight does the road-going RG500 Gamma claim?
  Suzuki claimed 95 hp and 72 Nm at 9,000 rpm, for a dry weight of 154 to 156 kg depending on the source. Period measurements showed more like around 78 hp at the rear wheel, and a little over 180 kg fully fuelled.
• RG500 Gamma or Yamaha RD500LC: which is closer to a Grand Prix machine?
  The Suzuki. Arriving a year after the Yamaha, it takes over the rotary-valve square four and the aluminium frame of the factory RGs, claims more power (95 hp against 88) and weighs distinctly less, at the price of a far more radical riding position.
• Why did the RG500 Gamma disappear so quickly?
  Because of the tightening of emissions standards, which condemned big road-going two-strokes — and it was never officially imported into the United States, for that matter. In-house competition from the GSX-R750, just as fast but far more liveable day to day, did the rest.

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