Bridgestone 350 GTR
‘The GTR, introduced in European markets in 1967, was one of the most sophisticated bikes of its day, featuring a disc-valve induction parallel twin engine as well as a generally high quality of construction’
The glory of what could have been
ACCELERATING OUT OF A curve with the little two-stroke twin revving eagerly, sun gleaming off its chromed petrol tank and a high-pitched exhaust note providing a vivid soundtrack, it was easy to understand why Bridgestone’s 350 GTR was so highly regarded 50 years ago. And it was sad to think that this model was the high point for a firm that abandoned motorcycle production shortly after it was built.
The GTR, introduced in European markets in 1967, was one of the most sophisticated bikes of its day, featuring a disc-valve induction parallel-twin engine as well as a generally high quality of construction. Even now, it impresses with its neat looks, crisp performance and reliable handling.
Yet not long after this bike was built, Bridgestone not only ceased production of the GTR but gave up making motorbikes altogether, to concentrate on the tyres for which the Japanese company is still well known. After riding the twin, that decision seems strange, although it makes more sense when you realise that in 1968 the GTR cost more than BSA’s Thunderbolt 650 parallel twin and only slightly less than a Triumph Bonneville.
The GTR was good all right, but in most people’s minds it wasn’t that good. Many motorcyclists were unconvinced about the appeal of the relatively little-known Japanese company and its flagship two-stroke twin, with the result that the GTR was sold only in a small number in the USA and even smaller in Europe before production ended in 1969.
The most notable aspect of the GTR’s 345-cc parallel twin engine was its rotary disc valve induction system that allowed much more precise control of gases than the more simple piston-ported design then used by rival two-stroke roadsters. Ironically, Bridgestone’s Japanese rival Suzuki had considerable experience of disc-valve racing two-strokes, but the firm’s 250-cc Super Six roadster, also a two-stroke twin, was piston ported. Suzuki’s knowledge dated back to 1961, when noted MZ factory racer and engineer Ernst Degner had defected from East Germany, bringing his team’s secrets with him.
Bridgestone’s twin used a disc valve (one for each cylinder) on each end of its crankshaft, with a 26-mm Mikuni carburettor bolted outside each valve. Another neat feature was the ‘piggy-back’ alternator, situated above the engine rather than at the end of the crankshaft, which allowed the GTR unit to be quite slim despite its side-mounted carbs. Peak output was normally claimed to be 37.5 PS at 7,500 rpm, although the figure of 40.5 PS was also quoted in places. (Most manufacturers were optimistic with power and speed claims, and Bridgestone seem to have played that game enthusiastically.)
The GTR’s advanced engine features did not end with its induction. Lubrication was by a Yamaha-style pump-operated system, to which the Bridgestone added the refinement of inspection windows for both engine and gearbox oil. Similarly, the GTR impressed with its six-speed gearbox and with its facility to swap the gear-lever and rear brake pedals to give a left- or right-foot gear change, both of which were commonly used at the time.
However, the Bridgestone also annoyed because its neutral was placed at the top of the six-speed gearbox, instead of between first and second as on most bikes. Similarly, although the GTR was unusual in allowing the rider to start the engine in any gear provided the clutch was pulled in, the kick-starter was inconveniently placed on the left of the bike. (More thoughtful details included stainless steel front mudguard and lubrication points on control cables.)
The rest of the GTR was relatively conventional. Its twin-downtube steel frame, gaitered front forks, chromed twin shocks, and 19-inch wheels with drum brakes front and rear were very much standard fare when the GTR was first sold in the American market in 1966. Visually it was similar to its 90-cc and 175-cc siblings, and there were also models with off-road styling, notably the 350 GTO which was built in an even smaller number than the GTR.
Few Bridgestones can have survived in better condition than this 1967-model GTR, which was originally exported to the USA. The bike looked superb and felt light, slim and quite tall as I stood alongside it and fired the two-stroke motor into life with a gentle swing on the kickstarter. The disc-valve engine immediately settled to a reliable tickover and felt just as well sorted when I set off, mildly disappointed that the dry clutch displayed none of the wheelie-provoking sharpness reported in some contemporary press coverage.
That unusual gearbox arrangement caused a few hiccups when I went to pull away and found myself in neutral. But generally the GTR was very easy to ride, feeling pleasantly responsive through the rev range, with no evidence of the vivid two-stroke power step that I’d expected. With 40.5 PS on tap even if you accept the higher of Bridgestone’s claimed figures for the GTR, the twin was hardly powerful by modern standards. But it was still lively enough to be fun, and to make me understand why the model impressed most people who rode one when it was new.
Back in the late 1960s, the Bridgestone’s revvy motor and light weight of just 161 kg made the two-stroke a match for almost any bike away from the line, which boosted its popularity in the States. Bridgestone quoted a standing quarter-mile time of 13.7 seconds. Even though it wasn’t really as quick as that, the GTR provided plenty of acceleration away from the lights — and if the front wheel did come up occasionally to produce that ’60s rarity of a wheelie, I can’t imagine many wide-eyed owners would have complained.
Top speed was about 150 km/h, rather than the 170 km/h or so quoted by some Bridgestone sources. More to the point, the GTR was happy to cruise at a steady 100 km/h or more, feeling smooth thanks to its rubber-mounted engine. Making the most of its performance meant sticking to fifth gear on the straights rather than using the overdrive sixth ratio, which cut speed unless the bike had the benefit of a hill or tail wind.
Inevitably, the upright riding position dictated by the Bridgestone’s fairly high and wide handlebars would have made high-speed riding tiring, though this was hardly a criticism in the days when fairings were rarely fitted as accessories, let alone as standard. On my ride the bike was comfortable enough, thanks to a reasonably well-padded seat,
plus suspension that was reasonably firm without being too stiff.
Handling was good by contemporary standards, thanks also to a twin-cradle steel frame that was rigid enough to prevent the notorious head-shaking suffered by some rival two-strokes. (Who mentioned Kawasaki?) Neither the forks nor the shock units had any adjustment, even for preload, but the shocks could be tuned by moving the top mounts, with the ride getting firmer with the units set vertically. This bike’s angled-forward units weren’t too far out for my 85 kg.
Similarly, the GTR’s drum brakes worked quite well, with even the twin-leading-shoe front unit that was borrowed from the firm’s 175-cc model providing reasonable stopping power. I also had no problem with the 350’s tyres, which predictably enough were Bridgestones, and gripped well despite their narrow size (though it would probably have been a different story in the wet).
Unfortunately for Bridgestone, the GTR’s quality came at a high price, for the bike cost considerably more than rival Japanese twostrokes, and was competing directly with larger engined four-strokes. It also faced resistance from riders who were dubious about a highperformance two-stroke’s reliability. This concern was not unreasonable, given the problems that early motors had with oil seals, and with broken air-filter parts being sucked into the engine.
Relatively small numbers were sold in the US, following the model’s introduction there in 1966. Towards the end of the following year the GTR went on sale in Europe, but sales were again slow. By 1968, Bridgestone was coming under pressure from rival Japanese marques which were also customers for its tyres, the company’s most important product. (Bikes were only ever a sideline.) Shortly afterwards, Bridgestone quit bike manufacture to concentrate on tyres.
The GTR was gone, leaving a lasting impression with those who had ridden one. Given Bridgestone’s success in the tyre world over the last few decades, it’s hard to argue with that decision to quit motorcycle production. But after riding this quick and classy machine, I can’t help wondering how good modern Bridgestones would be if the firm that created the 350 GTR half a century ago were still building bikes.
The narrow Bridgestones on the 350 GTR provided commendable grip
The rubber-mounted engine ensured smooth cruising
Front brakes borrowed from 175-cc sibling
Evident beauty did justice to the swansong
Quality is what priced the GTR above its rivals