BRIDGESTONE 350 GTR
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| BRIDGESTONE 350 IN RED & SILVER PAINT |
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.
BRIDGESTONE 350 GTR
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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