One man’s vi­sion and an­other’s hard graft turned Suzuki’s 500 GP bike from pretty also-ran into the ti­tle-win­ning best in class

Classic Bike (UK) - - CONTENTS -

How Suzuki’s twin-crank 500cc V4 went from slow and fickle to world dom­i­na­tion

Anew chap­ter in Suzuki’s rac­ing his­tory be­gan on Au­gust 23, 1986. The pro­to­type RGV500 XR71 was un­veiled dur­ing the San Marino GP, fol­low­ing months of spec­u­la­tion about Suzuki’s plans. This was a se­ri­ous state­ment of in­tent – not only was the fac­tory con­firm­ing its com­mit­ment to Grand Prix rac­ing, it had also built a bike un­like any Suzuki be­fore.

Their square-four, ro­tary-valve RG500 two-stroke had been at the front of GPS since the mid-1970s, both for the fac­tory and pri­va­teers. How­ever, Suzuki hadn’t won the premier-class ti­tle since 1982 with Franco Uncini, and stopped mak­ing cus­tomer-spec ma­chines in 1983. Fac­tory-backed teams slogged on un­til ’86, but the RG was out­paced and Suzuki man­age­ment wanted to pull out; 500s had be­come a costly high-tech power strug­gle, so they wanted to fo­cus ef­forts on street-based four-stroke rac­ers, which had added im­por­tance given the launch of the GSX-R750 in 1985. There was a valiant rear­guard ac­tion from within the fac­tory team, how­ever.

Led by road rac­ing man­ager (and former GP win­ner) Mit­suo Itoh, a two-stroke fac­tion re­sisted cor­po­rate pres­sure. The un­ex­pected suc­cess of the road-go­ing RG500 race replica al­lowed Itoh to make the point that a two-stroke GP pro­gramme could have com­mer­cial as well as pro­mo­tional ben­e­fits, so the pre­tence was main­tained that a new two-stroke racer could be a pro­to­type for a fu­ture Suzuki road­ster. Fol­low­ing Yamaha’s lead, Itoh’s all-new RGV500 XR71 used a twin-crank V4 lay­out – ef­fec­tively two par­al­lel twins, one be­hind the other, with cranks geared to­gether and the banks of cylin­ders set at an 80˚ an­gle. Un­like the Yam, its cranks ro­tated in the same for­ward di­rec­tion, ne­ces­si­tat­ing the use of an in­ter­me­di­ate shaft. It mea­sured 56 x 50.7mm (di­men­sions used through­out the RGV line) and was the first Suzuki with reed-valve in­duc­tion. Flat-slide Mikuni mag­ne­sium carbs were like the Yamaha’s, but with larger chokes and a dif­fer­ent slide mech­a­nism. Suzuki’s proven elec­tron­i­cally-op­er­ated Power Cham­ber sys­tem gave vari­able ex­haust di­men­sions, with an out­put of over 140bhp at 11,500rpm. Engine weight was given as 50kg, so a

best-guess over­all weight was 130kg – not bad, but the limit was 120kg, and Suzuki’s first proper at­tempt at a mod­ern twin-spar frame looked large and heavy. Forks and shock were by Kayaba.

Itoh said they wanted more power than the old RG but also a smoother de­liv­ery, and test rid­ers re­ported lots of midrange and a smooth tran­si­tion into the power. How­ever, they also said the engine was re­luc­tant to rev, with ground clear­ance lim­ited by bulky lower ex­hausts.

With new cylin­ders and crankcases cre­ated over win­ter, Suzuki’s RGV500 made its race de­but as the XR72 at a wet Ja­panese GP at Suzuka in March 1987. Test rider Takumi Ito made fine use of the easy power de­liv­ery to fin­ish third. When Kevin Schwantz, fit­ting in a few GPS while try­ing to win the US Su­per­bike ti­tle, fin­ished fourth at the next race in Spain, it seemed Suzuki had hit the ground run­ning. But the twisty Jerez track favoured the RGV’S midrange and dis­guised its lack of top-end speed – full-time rider Kenny Irons strug­gled to be com­pet­i­tive for the rest of the sea­son, and suf­fered many me­chan­i­cal grem­lins.

Suzuki went big time in 1988, se­cur­ing back­ing from Pepsi cola and sign­ing Schwantz for his first GP sea­son. Their new XR74 ver­sion of the RGV had mod­i­fied cylin­ders, new ex­hausts (with both lower pipes ex­it­ing on the right), and a be­wil­der­ing choice of ra­tios for the ex­tractable six-speed gear­box. The frame was al­tered, Showa sus­pen­sion re­placed Kayaba, and weight came down. Suzuki claimed over 150bhp at 12,300rpm, yet the engine was as rideable as ever – Schwantz won the first race of the sea­son at Suzuka, and won again at a damp Nür­bur­gring. He made the ros­trum at other races, yet only fin­ished eighth in the cham­pi­onship; de­spite a con­tin­u­ous flow of parts all sea­son, his Suzuki was still hand­i­capped by its top end. More speed needed...

The so­lu­tion was a com­plete re­design for 1989. The XR75 had counter-ro­tat­ing cranks, can­celling vi­bra­tion and un­wanted gy­ro­scopic forces, sav­ing weight and


re­duc­ing fric­tion. Al­ter­na­tive chips for the ig­ni­tion and power valves gave a choice of power curves, even smoother power and a wider spread of drive, with over 160bhp at 13,000rpm. The V4 was more com­pact, too, with a nar­rower 65˚ V-an­gle. It sat fur­ther back in a lighter chas­sis that saved 10kg and went back to Kayaba sus­pen­sion, with new up­side-down forks. This more re­spon­sive and for­giv­ing bike com­pli­mented Schwantz’s style and he won six of the sea­son’s 15 races. How­ever, the Texan suf­fered three break­downs in cru­cial races, and al­though the power gap to ri­vals had nar­rowed it was at the ex­pense of a fiercer de­liv­ery. The power band was only 2500rpm wide, mak­ing the bike very hard to ride and ex­pos­ing prob­lems in the chas­sis. Lucky Strike cig­a­rette money ar­rived for 1990, along with a heap of tech­nol­ogy. As power spi­ralled up­wards, Suzuki headed elec­tronic de­vel­op­ment with a so-called ‘trac­tion con­trol’ sys­tem on Schwantz’s new XR76, in which ig­ni­tion and/or power-valve open­ing al­tered de­pend­ing on gear, revs and throt­tle open­ing. Weight was slashed again, so much so that the V4 was un­der the new 115kg limit at the sea­son’s open­ing race. The RGV was now a se­ri­ous con­tender, and with Schwantz backed by a team-mate ca­pa­ble of get­ting on the ros­trum (Niall Macken­zie) it looked good for Suzuki. Un­for­tu­nately, where Kevin found it easy to fine-tune his chas­sis the pre­vi­ous year, the 1990 bike was dif­fi­cult to set up for each track. He strug­gled with it for the whole sea­son, and along­side five wins came five crashes. With a re­vised 130kg limit for 1991, the XR77 was an­other com­plete re­design. It didn’t lack power, but the RGV had lost its pre­vi­ous weight ad­van­tage and now be­came even more sen­si­tive to sus­pen­sion and ge­om­e­try. It strug­gled with grip. And de­spite pre­vi­ously be­ing ahead on tech, Suzuki were now the only works team with­out on­board teleme­try. Schwantz won five races, but had to ride the wheels off an un­der-per­form­ing bike to end third in the ti­tle chase. Things didn’t im­prove in 1992 – Kevin only won one race in an in­jury-hit sea­son. It was also ob­vi­ous from Mick Doohan’s run of early-sea­son vic­to­ries that Honda had made a quan­tum leap in tam­ing a vi­ciously pow­er­ful, feath­er­weight bike with their ‘big bang’ NSR500 (Doohan looked guar­an­teed champ, but a crash at Assen wrote off his sea­son). The ‘big bang’ idea was that a closer fir­ing in­ter­val helped trac­tion; 500s were hardly short on power, and closer fir­ing gave the tyre more chance to ‘re­cover’. It was a huge stride for­ward in mak­ing a 170bhp bike into a rideable, for­giv­ing pack­age. Suzuki were first to re­act to the NSR, per­haps be­cause they ex­per­i­mented with the same idea back in 1978... be­fore re­ject­ing it. Their re­sult­ing 70˚ big-bang V4 ar­rived in May ’92 and was fast and very rideable; only Schwantz’s in­jury and crash­laden sea­son pre­vented its at­tributes be­ing truly shown. The fi­nal piece of the jig­saw wasn’t new ex­hausts or fresh ge­om­e­try, but a change of prac­tice at Suzuki. Their modus operandi had been to de­cide what

im­prove­ments they needed the fol­low­ing year, de­sign a new bike around them – of­ten with­out back-to­back com­par­i­son to the old bike – then hope to get it fin­ished in time for a spot of test­ing be­fore the sea­son. But race en­gi­neer Stu­art Shen­ton knew bet­ter. Re­cruited in 1992, he was a former Honda tech­ni­cian who had worked with HRC since Fred­die Spencer’s dou­ble 250/500 cham­pi­onship sea­son in 1985, and un­der­stood the value of lin­ear de­vel­op­ment rather than sweep­ing changes. Schwantz des­per­ately wanted more off-sea­son test­ing, mir­ror­ing Shen­ton’s em­pir­i­cal phi­los­o­phy, and to their credit Suzuki changed their pol­icy ac­cord­ingly.

The 1992/93 close sea­son was the first with Shen­ton on­board, and a very dif­fer­ent win­ter’s test­ing. “We started two weeks af­ter the fi­nal GP of ’92 and ran up to two weeks be­fore the open­ing ’93 round,” Shen­ton told me. “It was the most com­pre­hen­sive sched­ule Suzuki had ever un­der­taken. We built on the strengths of the pre­vi­ous year’s bike and pro­duced an im­proved ver­sion, rather than throw­ing it away and start­ing again, as they al­ways used to. The chas­sis we started the sea­son with was al­most iden­ti­cal to the ’92 bike, and the only up­date all sea­son was a new one for Jerez which had a wider range of ad­just­ment.”

Evo­lu­tion, not revo­lu­tion, ap­plied to the engine as well. The XR79 ver­sion of Suzuki’s twin-crank V4 was closely based on 1992’s big-bang XR78, apart from mag­ne­sium crankcases in­stead of alu­minium. This saved 2kg, al­low­ing the team to add weight­ier, stiffer parts else­where – bet­ter swingarm bear­ings, an im­proved shock link­age. They could add new bits, too, with a quick­shifter for rapid-fire gearchanges. More than 165bhp reached the rear tyre at 12,800rpm, a few revs higher than the pre­vi­ous sea­son, yet with­out sac­ri­fic­ing tractabil­ity. The two-stroke would climb from un­der 7000rpm right up to 13,600 in a seam­less, step­less, glitch­free ram­page. Now be­ing able to rev 1000rpm be­yond peak power also aided use­abil­ity, sav­ing a cou­ple of gearchanges at twisty tracks like Jerez. Suzuki al­ways knew what its V4 needed, it just hadn’t gone about it the right way; now, thanks to evo­lu­tion and metic­u­lous test­ing, the 1993 RGV500 was fast, user-friendly and more re­li­able than ever. I tested Schwantz’s bike hav­ing rid­den all its op­po­si­tion, and it was the most re­fined, com­plete and rideable of all. It didn’t quite have the raw power of the NSR, but was a more con­fi­dent, eas­ier-han­dling bike. The engine was smooth and lin­ear, yet at the same time so strong and pow­er­ful; it changed di­rec­tion bet­ter than ri­vals, with very neu­tral steer­ing; and it in­spired con­fi­dence, in spite of awe­some per­for­mance. A truly adapt­able pack­age.

Schwantz rode a bril­liant and con­trolled sea­son to win the 1993 ti­tle, and was a wor­thy cham­pion. Yet credit must also be given to Itoh and Shen­ton, whose de­ter­mi­na­tion and pa­tient evo­lu­tion made Suzuki’s RGV500 XR79 the class of the pack.

Pretty? Oh yes. But early bikes were also out­paced and fickle. This is the XR75 in 1989

RIGHT: Au­gust 1986, and the break­away two-stroke fans in Suzuki’s race team re­veal their new V4

BE­LOW: Mit­suo Itoh was a fac­tory GP rider and win­ner of the 1963 50cc TT

Re­fined, use­able, fast, adapt­able and, cru­cially, re­li­able – by 1993 the RGV500 was a class act

LEFT: Kenny Irons on the first RGV in 1987. It worked on tight tracks, but lacked speed

Be­low: Smooth RGV car­ried Schwantz to a win at a very wet Nür­bur­gring in 1988

Above: Su­per­bike hot­shot Schwantz as a wild card in ’87, be­fore Pepsi cash

Suzuki were first to copy the ’big bang’ Honda, and the ’92 bike was fast and rideable

ABOVE: Tab-backed 1990 bike was so light it was un­der the 115kg class limit

Be­low: En­gi­neer Stu­art Shen­ton to­tally changed how Suzuki worked

Engine: 56 x 50.6mm V4, twin pressed cranks, nee­dle-roller big and small ends, sin­gle-ring pis­tons, reed valve in­duc­tion, flat­slide carbs Chas­sis: Fabri­cated twin-spar alu­minium frame, fully-ad­justable Kayaba shock and up­side-down forks, car­bon fi­bre brake discs

ABOVE: Mas­sive head­stock of XR79 used ta­per-roller bear­ings with in­serts to ad­just steer­ing an­gle

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