Bridgestone's quick and sophisticated 350 GTR two-stroke twin was produced only in small numbers for just a few years in the late 1960s, but it left a lasting impression on those who rode it. As well as arm-wrenching acceleration and agile handling, the GTR incorporated several advanced features that would later be adopted by other manufacturers.

The most notable aspect of the GTR's 345cc parallel twin engine was its rotary disc valve induction system, which allowed much more precise control of gases than the more simple piston-ported design then used by rival two-stroke roadsters. Ironically Bridgestone's rival Japanese company Suzuki had considerable experience of disc-valve racing two-strokes, but the firm's 250cc 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 26mm 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 37bhp at 7500rpm, although the figure of 40bhp was also quoted in places.

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 gearlever and rear brake pedals to give a left- or right-foot gearchange, both of which were commonly (and confusingly!) used at the time.

But the Bridgestone 350 GTR 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 kickstarter was rather inconveniently placed on the left side of the bike.

Such details were soon forgotten on the move, because the Bridgestone's exhilarating performance made the two-stroke a match for almost any bike away from the line. The high-revving power was allied to light weight of just 3301b (150kg), which added to the acceleration. Coupled with a slightly grabby clutch, this could occasionally result in that 1960s rarity of an unplanned wheelie.

But the GTR felt impressively composed and refined at higher speeds. Its slightly too tall sixth gear kept top speed down to about 95mph (153km/h). But the reasonably broad spread of torque, combined with the rubber-mounted motor's smoothness, allowed easy cruising, with speed limited mainly by wind pressure due to the upright riding position.


High build quality


Handling was also very good by contemporary standards, thanks to a stiff twin-cradle steel frame, and suspension whose high quality typified the thorough way in which the whole bike was put together. Similarly, the GTR's drum brakes worked well, especially the twin-leading-shoe front unit.

Unfortunately for Bridgestone GTR quality came at a high price, for the bike cost considerably more than rival Japanese two-strokes, and was competing directly with larger engined four-strokes. It also faced resistance from riders who doubted a high-performance two-stroke's reliability. Only small numbers were sold in America, following the model's introduction there in 1966. Two years later it went on sale in Britain but shortly afterwards Bridgestone, whose main business was making tyres rather than motorcycles, quit bike production altogether.

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