Bridgestone 175 Dual-Twin and 175SS street scrambler – a rare 1960s two-stroke twin

Steve Cooper turns his attention to Bridgestone’s 175cc twin – a technically advanced and now rarely seen machine from the 1960s.

Bridgestone may be best known for its larger-capacity machines such as the GTO 350 and GTR 350, but the firm’s smaller twins are arguably just as rare today. Among these was the 175 Dual-Twin, first unveiled at the 1965 Tokyo Motor Show.

The 175 shared its basic architecture with the company’s smaller machines but featured twin cylinders with bore and stroke dimensions of 50mm x 45mm. The engine produced around 20bhp at 8000rpm, giving the bike a strong performance for its class. Weighing a quoted 123kg, the 175 delivered an impressive power-to-weight ratio, covering the standing quarter mile in approximately 17 seconds and achieving a top speed in the mid-70mph range.

Built to a high specification rather than down to a price, the 175 Dual-Twin featured disc valve induction, hard chrome-plated cylinder bores and a two-stroke oil injection system. One of its most distinctive features was its dual-purpose gearbox. Using a lever on the left-hand side of the engine – known as the ‘Sport Shift’ – riders could select either a four-speed rotary gearbox or a conventional five-speed layout. In rotary mode, pressing down from top gear selected neutral and then first gear, while switching to five-speed mode placed neutral between first and second in the usual fashion.

The 175SS followed the established street scrambler formula, with braced handlebars, a bash plate and high-level exhausts fitted with peashooter silencers. Bridgestone also produced a limited number of competition-focused versions, marketed as the 175+ Racer or Hurricane. These machines were stripped of road equipment, fitted with cut-down mudguards – the front mounted from the bottom yoke – and equipped with satin black expansion chambers. Performance upgrades are believed to have included revised carburation, modified disc valves, hand-finished porting and potentially higher-compression cylinder heads. Running on block-pattern tyres, the Racer proved highly competitive in its class on American TT dirt tracks.

Towards the end of the 1960s, at the request of US importer Rockford Motors of Illinois, the 175SS received cosmetic revisions. The original chrome and candy red finish was replaced by a mid-green and white scheme and marketed as the Mach II SS-7. This was later updated around 1970 to the Mach II SS1. Although badged as a 200, the engine capacity remained unchanged at 175cc. Updates were largely limited to styling, including satin black silencers and revised paintwork in silver or white.

Despite its technical sophistication, the 175 range failed to achieve strong commercial success. Bridgestone’s motorcycle division was operating under significant financial strain, with production costs poorly controlled and sustained losses impacting the parent company. By 1971, motorcycle production ceased entirely as Bridgestone refocused on its core tyre business.

Today, Bridgestone motorcycles are exceptionally rare. While the larger 350cc models have achieved near cult status, the 175 twins – particularly the SS variants – remain comparatively overlooked. Although many street scramblers of the era leaned more towards style than outright off-road capability, the 175+ Racer stood apart as a genuinely capable competition machine. Even now, it remains a fascinating and highly desirable example of 1960s two-stroke engineering.