Copyright Jan Burgers printed on 250gsm Kodak paper
April 29, 1973, marked the beginning of the end for upright twin shocks in modern motorcycle design.
How so? This historically pivotal image of Roger De Coster riding a factory Suzuki RH250 at the 1973 Belgian Grand Prix was captured at the third round of the '73 world 250cc championship at Wuustwezel.
Swede Hakan Andersson debuted Yamaha's all-new single-shock cantilever suspension system that weekend. He secured a 1-2 moto finish on the radical YZ250 to claim his first GP of the year, dominating the remainder of the season with 10 more moto wins to lift Yamha's first-ever world motocross title. It was rumoured De Coster took time out from his heavy 500cc schedule to track the whoop-eating Yamaha up close and personal aboard this Suzuki 250 at Wuustwezel.
He looked on at Yamaha's new weapon with envy and frustration.
When Yamaha learned that the cantilever idea had been rejected by Suzuki, it swooped and had a prototype developed by Torsten Hallman by early 1973, and a race-ready bike by April.
Belgian engineer Lucien Tilkens first developed the long-travel system in 1971, and offered it to Suzuki. It tested the single-shock concept with De Coster and Suzuki teammate Sylvain Geboers. They both liked it, but Suzuki dithered after considering building its own long-travel technology, a decision that would cost them in more ways than one. After witnessing the runaway success of Yamaha's cantilever system - the very system that they had wanted for their factory Suzukis - De Coster and Geboers took matters into their own hands by modifying their RH500 frames and developing new rear-suspension geometry
The first production monoshock Yamaha was the 1975 YZ250B motocrosser. After building a small number of monoshock YZR750, 500 and 350cc works racers in 1975, Yamaha released its first production monoshock road racers in 1976, the Yamaha TZ250C and TZ350C. This was followed by the 1977 DT250D and DT400D trailbikes, the first road-going models to sport Yamaha’s monoshock system.
Other Japanese factories soon developed their own single-shock systems; Honda’s Pro-Link, Kawasaki’s Uni-Trak and Suzuki’s Full-Floater. In 1981, Suzuki was forced to pay teenage Full-Floater inventor Don Richardson $US19m for misappropriating two trade secrets belonging to him.
De Coster won his third consecutive World 500cc Championship with Suzuki in 1973 after overcoming a mid-season surge by Maico's Willi Bauer who had swept the Czechoslovak and US GPs, as well as Belgium. Going into the final race of the season at Sint Anthonis, Holland, Bauer still held the points lead.
The Sint Anthonis track was composed of deep sand, which robbed engines of power and increased fuel consumption. A Suzuki engineer calculated that its petrol tanks did not have sufficient capacity to finish the race. De Coster took one of the spare tanks and drove two and a half hours to have it modified to increase its volume. He then drove back in time for the race. Despite little sleep, De Coster scored two fourth-place finishes while Bauer suffered a mechanical failure, handing De Coster the title.