No contest! There can only ever be one contender for the accolade of the ultimate British single on road or track. And that is the final evolution of the series of special-framed Matchless G50! Ridden by the legendary rider/engineer Peter Williams and built by revered tuner Tom Arter.
Peter finished second no less than four times in the Isle of Man Senior TT between 1967 and 1973, most frequently to Giacomo Agostini’s MV Agusta. It was a feat he repeated often enough at classic Grand Prix circuits like Assen, Monza, Hockenheim and Dundrod to allow him to lead the 1967 500cc World Championship points table on the Arter G50 after the first three races of the season ahead of Mike Hailwood on the Honda four and Ago’s MV triple!
Built by Tom Arter in 1969 when the era of the British single was most decidedly over (although nobody told him and his studious-looking bespectacled rider that!), the final version of the bike was better known to race fans of the day as ‘Wagon Wheels’. This nickname recognised its pioneering status as the first bike to utilise cast alloy wheels. These were, in fact, designed by Williams himself at a time when wire-spoked wheels were the norm.
Coupled with the equally ground-breaking use of disc brakes and wind-cheating slim-line bodywork, the Arter G50 was a truly visionary machine created by two passionate but expert engineers – one of whom also raced it! The bike prolonged the competitive life of the four-stroke single well beyond the advent of the two-stroke era and Williams’ fastest Isle of Man TT lap of 102.74 mph, set in finishing second to Jack Findlay’s two-stroke Suzuki twin in the 1973 Senior race, was to last until 1997 as the fastest lap of the Mountain course by a single-cylinder machine.
Williams and Arter first teamed up in 1966, ultimately running a pair of 350/500cc bikes fitted with 350cc AJS 7R and 500cc Matchless G50 engines that were essentially identical apart from their capacity. They first featured special Reynolds frames that master tube bender Ken Sprayson had built for World Champion John Surtees at the start of the decade as an insurance policy in case the MV Agusta team (for which John was riding) followed the lead of other Italian manufacturers and retired from racing. In the event, Surtees never used them because of his move to car racing, but when they were acquired by Tom Arter and put in the hands of Peter Williams, they immediately started delivering results; in fact, Peter won his debut international race in the North West 200 on the 500cc version.
Until then, he’d struggled to make his mark on an Arter-tuned standard Matchless G50 in UK national races – a fact he admitted to feeling rather shamefaced about, given that it was his father Jack Williams, then AMC’s chief engineer, who had been responsible for the creation of the Matchless G50 in the first place!
That problem was resolved in 1966 when Tom Arter acquired the Surtees Specials and rechristened them the Arter Matchless racers. On these bikes, Peter quickly became a world figure and a star protagonist in the hurly-burly world of British short circuit racing.
Sadly, however, a serious crash in the East German GP at the Sachsenring abruptly ended his 1967 season. During the full year of convalescence he needed to recover from his injuries, he began experimenting with creating the first cast magnesium wheels to be fitted to any motorcycle and further developing the use of the disc brakes designed by his friend Colin Lyster.
For the ultimate version of his racers, Tom Arter commissioned two new frames from racing car chassis constructor Grand Prix Metalcraft in North London. Their design broadly followed the twin-loop duplex cradle format of the previous Sprayson-built frames but used slightly narrower-gauge one-inch tubes rather than the inch and one-eighth diameter tubing of the Reynolds chassis. This saved weight, a vital objective for Williams with the reduced power of the Matchless G50 compared to the MV Agusta.
The bike’s single-cylinder, single overhead camshaft motor delivered 53 bhp at 7,250 rpm at the rear wheel, which was as good as any British single of the day but still some 20bhp down on the MV. Giacomo Agostini could generally win as he pleased at the end of the 1960s, and the primary aim of Tom Arter and Peter Williams was to be ’the best of the rest’.
They saw innovative chassis engineering as the key to this and used a swinging arm made of oval-section tubing—another motorcycling first. Coupled with the thinner wall section of the main (still round) frame tubes, this meant that the new chassis was not only lighter but also had an increased overall stiffness-to-weight ratio.
Fitted with ultra-slim bodywork, with cast magnesium wheels and a single disc brake at either end, the 1972 version of the bike weighed in at 292lb/132kg dry, the same weight as a standard G50 fitted with drum brakes and no bodywork.
After initially experimenting with a Ceriani fork, Williams settled on a Norton Roadholder front end. However, he redesigned the left leg of the Norton fork to incorporate a new slider that accommodated the fitting of the AP-Lockheed twin-piston brake caliper which gripped the 10-inch (254mm) Girling cast iron brake disc. The caliper was situated behind the fork leg in order to improve steering by bringing the centre of mass closer to the steering axis. Twin Koni shocks provided the rear suspension and were adjustable for damping as well as spring preload.
Next, the space between the fork legs was narrowed via special triple clamps, in order to allow the handlebars to be mounted closer together to reduce wind resistance.
Distinctive slots were cut in the flanks of the fairing to allow it to be wrapped around the rider’s upper body while still giving space for the ‘bar ends to rotate.
Williams then commissioned two fuel tanks for the bike. A small one-gallon one for short circuits and a larger one for GP and TT racing. As well as aluminium ducting that shovelled cooling air onto the engine via a narrow frontal slot in the fairing. This gave the Arter Special a distinctively lean and lithe look.
One other distinctive feature truly made it stand out in the late-1960s race paddocks: its hitherto unseen six-spoke cast magnesium wheels, manufactured to Williams’ design.
These were originally fitted to make it easier to mount the disc brakes and there was no weight saving advantage over conventional wire-spoked wheels. For the 1970 season, however Dunlop confirmed that Williams could dispense with inner tubes without compromising safety. This was originally aimed at lessening rolling resistance. However the resultant reduction in unsprung weight also offered enhanced suspension compliance as there were fewer kilos for the fork and shock to dampen.
Peter Williams putting the pressure on Giacomo Agostini at Brands Hatch
The lightweight wheel package was also a critical factor in improving the Arter G50’s steering, thanks to its diminished gyroscopic mass. Leaving out the inner tubes also improved acceleration and braking, thanks to reducing the moment of rotational inertia of the wheels. Their lower weight meant less inertia to overcome in starting the mass of the wheel rim moving under acceleration, as well as offering a similar benefit in stopping it, as there is less rotational mass momentum that must be brought to a halt. The same benefits apply today to carbon fibre wheels.
Peter Williams on his way to second place in the 1971 Isle of Man TT
All of this made the Arter G59 agile and nimble enough for Peter Williams to catch and pass Giacomo Agostini’s MV triple in the 1972 Hutchinson 100 at Brands Hatch, leaving the Italian maestro to fall off in vain pursuit of the flying single! No other single-cylinder racer had ever pushed any of the multi-cylinder Italian racers so hard. Surely the Arter Matchless G50 was the bike that did the most with the least!
Words and Photographs courtesy of The Motorcycle Files
For the full story of the Arter Matchless G50 we recommend Peter Williams Arter Matchless G50 – The Supreme TT Single the e-book in The Motorcycle Files series.
