4 years ago

Dirt and Trail July 2018 issue 2

  • Text
  • Durability
  • Bikes
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  • Enduro
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Why a four stroke? OK so

Why a four stroke? OK so most riders initial reaction would be to say that the thumpers are heavier than 2-strokes – and a few years ago you’d have been correct. But is that actually true? If you look at the data for the KTM EXC250 and EXCF 250, the four-stroke is a mere 3 kg heavier, which in the grand scheme of things is not vast. And in terms of the top capacities in each engine type, the EXC300 is only 6.5 kg lighter than the 500. Whatever might have been the case in the past, the weight differences are nothing like as marked as they used to be. Four-strokes have changed remarkably over the years. Gone are the pistons as big as bean cans and now modern thumpers have slim line pistons that are barely a centimetre deep, capable of moving at up to 12,000 rpm – that’s an astonishing 200 times a second! Faced with technology that seems more at home on Formula 1 cars, if you ride a modern four-stroke, the flexibility and response from the engine is staggering. From tick over to red line, the new breeds of four-strokes deliver a progressive and linear power curve that would have been unimaginable twenty years ago. And that’s what makes these so fun to ride in the bush… Present for duty on the day were the 250, 350 and 450 EXC-F’s. EXC means PDS system (no linkage), and wide-ratio transmission. F means four-stroke. The EXC-Fs were the last of the orange bikes to get the latest generation KTM frame/ engine/seat layout that has been on the SX models since the 2015. Now the SX/SX- Fs, XC/XC-Fs, and XC-W/EXC-Fs all have the same lightweight frame and lightweight engine configuration. Another way to look at it is that these bikes now have the exact same frame and engine DNA as Ryan Dungey’s race bike, which is pretty cool. 86 DIRT & TRAIL MAGAZINE JULY 2018

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