From frightening to refined
How Suzuki’s two-stroke four developed from an overpowered handful into a polished world-beater
‘POWER ARRIVED WITH THE SUBTLETY OF A SIZE 12 TO THE GROIN’
The FIM announced new Grand Prix rules in late 1967. These limited the number of cylinders in each class, and were especially hard on small capacity bikes. Having developed a 400bhp/litre 50cc triple and 125cc V4 for ’68 that were effectively obsolete overnight, Suzuki (along with Honda) withdrew from racing.
Private teams and importers carried on, however, with larger-capacity bikes based on Suzuki’s road models: the TR500 was a T500 twin, the TR750 was the GT750 triple. Success brought increased factory support; for ’73, Jack Findlay was a works rider and won the Senior TT, while Barry Sheene took the Shell Oils 500cc, MCN Superbike and FIM Formula One titles. Smitten again with racing, Suzuki then threw things into fast forward with a full-factory GP return and the legendary RG500.
RG500 SQUARE FOUR
Suzuki’s riders saw the RG prototype in Hamamatsu, Japan in early 1974. The new 500 was a water-cooled square four – think two parallel twins, one behind the other. Measuring 56 x 50.4mm, the 497.5cc two-stroke was effectively four 125s, with four cranks geared to a central primary shaft. Each crank carried a thin slotted disc to control supply from a side-mounted 34mm Mikuni carburettor. Front cylinders faced ahead with expansion chamber exhausts under the engine, with rear cylinders and pipes facing rearwards. The tubular steel frame carried an aluminium alloy swingarm and Kayaba suspension, with 18in wheels. Disc brakes were copied from Lockheed – odd piston sizes (17.4mm and 19.1mm) were due to being based exactly on their imperial design.
The prototype was wild, power arriving with the subtlety of size 12 to the groin. Sheene took 1.5 seconds off the test track record with this monster engine and overwhelmed chassis, later claiming the prototype was more powerful than his championship-winning bikes.
Refined slightly (and detuned) for the 1974 500cc GP season, the RG500 XR14 had 95bhp and was fast, but reliability wasn’t great; it ate primary drives and gearboxes, and often seized. High-speed stability wasn’t ideal. Engine niggles were ironed out for ’75 and Suzuki squeezed another 5bhp and 5mph, but Sheene’s horrific 175mph TR750 crash at Daytona was rather a setback... For 1976 the XR14 was much improved. New geometry of 54 x 54mm gave 494.7cc, and power jumped to 114bhp at almost 11,000rpm. Suzuki made it available to privateers with a spec close to factory bikes, though the official entries were virtually unbeatable – Sheene won half the season’s races and took the title, and Suzuki riders filled the next five places. A new RG at ’77 pre-season testing had a ‘stepped’ engine (front cylinders lower than rear) and quick-change cassette gearbox; Barry wanted to race it, but Suzuki wanted to see what Yamaha had at the first round, so kept the XR14 with new cylinders and air suspension (being tested for the GS1000). They also tested a ‘big bang’ XR14 with all four pistons rising together (a missile, but impossible to push start), but didn’t need that either – the Yamahas couldn’t stop the ‘old’ RG’S second title.
The ‘stepped’ RG did race in ’77, as the big-bore 652cc RGA700 in Superbike and Formula One. It reached the 500cc class as the RG500 XR22 in ’78 (privateer bikes were tagged RGB500), with 122bhp and 180mph potential. The more compact engine allowed a longer braced swingarm for stability, and it featured larger-diameter forks and bigger brakes. Suzuki had fewer works bikes, however, and with Sheene off-colour Yamaha took charge with their everimproving bike and a mouthy American by the name of Kenny Roberts. Tweaks to the XR22 couldn’t stop Roberts taking the 500cc title in ’78, ’79 and ’80. The third RG variant arrived for 1981. The XR35 had raised compression, larger 37.5mm carbs and 130bhp, a 16in front wheel for faster steering – and Marco Lucchinelli of Gallina Suzuki Italia won the title. There was a new box-section aluminium frame for ’82, and Franco Uncini (replacing Lucchinelli) claimed another championship for Suzuki.
The square four’s time was over, though. Suzuki was finding it harder to match Yamaha and Honda, so withdrew from competition in October ’83. The final 25 production RGB500S were made in ’84, and private and importer teams fought on. There were experiments with carbon frames, and Darren Dixon won the 1988 British F1 title on a Padgetts RG (the last stroker to win the British F1/ Superbike title). But its GP days were done.
RGV500 V4
Suzuki revealed the RGV500 XR71 prototype and announced their GP return in August 1986. At 56 x 50.7mm its geometry was almost identical to the first RG, but this bike was effectively two parallel twins geared together as a twin-crank V4. Cranks rotated the same way, requiring an intermediate shaft, with banks of cylinders sat 80˚ apart. Magnesium carbs had reedvalve induction, rather than disc valve, and an electronically-controlled Power Chamber system varied exhaust geometry. It had over 140bhp at 11,500rpm, but the reeds and cunning exhaust technology gave huge midrange and smooth power – the new V4 was a huge step from the light-switch RGS.
‘THE 1989 RGV500 WON RACES BUT ALSO BROKE DOWN QUITE A BIT...’
The V4 raced in 1987 as the XR72, with improved cylinders and crankcases, Suzuki’s first twin-spar frame and Kayaba suspension. Their test rider came third in the opening wet race and wildcard Kevin Schwantz was fourth in Spain, when conditions and circuits played to the V4’s midrange and rideability; a lack of power, pace and reliability made the rest of the season a struggle. Big changes for ’88 saw a heavily revised engine give over 150bhp at 12,300rpm without losing useability, plus Showa suspension. Schwantz (now full time in GPS) had four rostrums but the RGV was still slow next to the Honda, so there was a new 160bhp motor for 1989 with a 65˚ V-angle. Contrarotating cranks reduced vibes, and there was strong power from 9000rpm and a 13,700rpm limit. Chassis balance was altered, Kayaba suspension returned with upside-down forks, and it got carbon brakes. The RGV won six races, but also broke down quite a bit. Setting the Suzuki up was hard in ’90 and ’91. The new XR76 had almost 170bhp and was much lighter, but became increasing fickle – riders struggled with handling. When Honda introduced a big-bang NSR with close firing intervals for ’92, Suzuki were the first to respond as they’d tried the idea on the RG. The new big-bang RGV worked brilliantly, being fast yet useable – but crashes spoilt the season. The breakthrough came in 1993. Rather than start the season with a brand new bike, a winter of heavy testing ironed out issues with the existing one. Schwantz won the world title with the refined RGV500 XR79. Though they had a polished motorcycle, Suzuki still had two issues: Honda, and their rider Mick Doohan. The Australian dominated the 1994 season, winning nine out of 14 races and ending 150 points clear of Luca Cadalora’s second-placed Yamaha. With crew chief Jerry Burgess, Doohan won five back-to-back titles – and with no-one else standing a chance, development of other bikes slowed to a crawl. Suzuki regrouped in autumn 1998. Signing Kenny Roberts Jr and engineer Warren Willing (ex-roberts Sr) for the following year, they designing a new RGV. The big-bang twin-crank 80˚ V4 had magnesium cases, solenoid-controlled power jet carbs, and two power valves: a guillotine, like Yamaha’s YPVS, and a rotary valve to open a secondary expansion chamber for torque. The 192bhp motor hung from an alloy frame with adjustable swingarm pivot height, steering angle, fork offset and subframe height, with Showa suspension. Roberts blitzed 1999’s opening rounds, breaking Suzuki’s four-year win drought, and finished the season second. The next year his RGV500 XR89 won the championship, bringing Suzuki their last GP title and signing off the two-stroke GP era on a high before 2002’s four-stroke Motogp revolution. Turn over for what the last RGV500 is like to ride