Following my most recent blog concerning Lang Hindle, the 1970s and the very rare Tri Mil Racing frame, a couple of readers contacted me to talk about other rare chassis. Custom-built designs have always been the exception rather than the rule in racing, particularly in North America. In Europe, specifically in France and the UK, the custom-built bike was more common, and the wacky French endurance scene produced some unusual layouts.
In North America, most frame mods involved improving a standard design already in use. Much has been made of the lack of road holding manners that plagued Japanese sports bikes in the 1970s. In truth, it would be fair to say that performance (meaning engine output) simply pulled away from the chassis designers – that is, until the mid-1980s at least.
Long before adjustable compression or rebound anything, well before today’s at-the-track suspension gurus, the best handling production bikes tended to have long wheelbases, stiff frames, conservative geometry and torquey twin-cylinder engines. This covers most Ducatis, as well as Laverdas, Moto Guzzis etc. from the era.
Those racing the more powerful inline 1970s O.E. four cylinders, particularly the Kawasaki and later Suzukis tricked out by Yoshimura, were forced to try and improved their chassis’ configuration. This involved changing the steering geometry, bracing the frames, beefing up the swing arms, laying down the twin rear shocks and improving suspension travel where possible.
Soon, the privateers copied the “A” team mods, and Lang Hindle hit on a successful geometry formula for his Kawasaki Z-1 Superbikes. However, unlike some builders, Hindle didn’t believe in too much bracing or giant engine mounts that turned those gigantic air-cooled mills into stressed chassis members.
Perhaps the wildest "improvements" ever performed (or at least ever approved by the technical inspectors) in AMA superbike involved the works 1976 factory BMW R90S, some of which raced with mono-shock rear suspension inspired by the breakthrough Yamaha GP design. In production form, the BeeMm came with vertical twin shocks, but getting a shaft drive bike to win on the race track was quite an achievement, regardless of the tricks employed.
BMW officially withdrew after taking the inaugural ’76 Superbike crown in the US, and didn’t return to the SBK class until the advent of their own four-cylinder in-line S1000RR, waaaay back in 2010!
Meanwhile, the ‘70s privateer bike of choice for the featured Formula 750/Formula One category was Yamaha’s long-serving TZ750 four-cylinder two-stroke, which you will read about in more detail in Graham Clayton’s upcoming Rapid Classics feature in the April issue of Inside Motorcycles (available in early March). Tire, chassis and suspension development on road racing machines really came into its prime thanks to the big Yamaha, although it took years for all the tricks to filter down to the privateers.
While Kenny Roberts bitched about not getting his full works, unobtanium YZR750 to handle, the owners of the later production TZ750s (D through F models) did their best to imitate every part ever viewed on the rare works bikes of Roberts, Steve Baker, Skip Akslund and world champ Johnny Cecotto.
Special swingarms were constructed to clear the larger rear wheels and tires, while the counter shafts were spaced out, chain runs revised and the trick, crossover, three silencers on one side exhaust layout was also replicated. The '70s-era Yamaha stayed competitive well into the 1980s, and by that time some brave souls even experimented with the newfangled 16-inch front wheels. Power was ever increasing, so making rear slicks last was a major, ongoing concern.
Perhaps the most aggressively developed Yamaha TZ750 was the final bike campaigned by Canadian Miles Baldwin in the AMA F-1 series in 1983. With help from famed Boston-area builder Kevin Cameron, hardcore privateer Baldwin almost snatched the AMA crown from the works Honda of non-relative Mike Baldwin.
“Milo’s” Yamaha was well used and well travelled, bought from Mike Baldwin at the end of the 1978 season. In fact, it was the bike that Mike used to win the Mosport F-750 World round at the end of 1978, launching Mike’s works racing career.
Nearing the end of its storied career, Miles Baldwin’s TZ was heavily massaged by Cameron, improved in every way. Eventually the bike featured a one-off, heavily modified chassis, complete with bell crank-actuated swing arm. This is perhaps the most exotic and rare “production” Yamaha TZ750, although no doubt someone has it hidden away in a barn somewhere. Anyone heard anything?