IS BIGGER BETTER?
The US dirt bike cottage industry swung into action on the back of the BSA B50 and Triumph TR5MX – and Triumph joined the aftermarket performance gold rush, offering a 570cc big bore kit through their dealer network; Cycle magazine fitted one to their test bike and put it through beforeand-after dyno runs.
The results were impressive. The stock engine made 24.23bhp at the rear wheel; with a less restrictive exhaust and the 570cc conversion, it leapt to 36.01bhp. Peak torque (at 5000rpm) showed a similar hike, with the big-bore motor pumping out 34.81lb.ft compared to 26.1lb.ft. ‘What a gas: what an absolute rocket ship,’ raved Cycle.