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’

Bike India - - CONTENTS - WORDS: ROLAND BROWN | PHO­TOG­RA­PHY: PHIL MASTERS

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

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