To an outsider, off-road biking comes in indistinguishable categories such as motocross, trail riding, trials, enduro and grass track racing. It is important, then, to clarify what motocross isn't. It's not bouncing through rocky streams at two miles an hour trying to keep your feet off the ground (trials), it's not a race through forests against people who dream of one day doing the Paris-Dakar (enduro), it's not a motorised amble down the green lanes of Britain (trail riding), and it's not speedway on mud (grass track).
Motocross is about pressurising the machine in pursuit of speed and mobility on a rough terrain. At the Doncaster Motor Parc, Finningley, Yorkshire, they know about rough terrain. Ed Bradley, 22, has taken a piece of wasteland owned by his parents' building company and turned it into one of the most challenging runs in the North. The one-mile circuit consists of steep berms (banks), hairpin bends, rutted straights and bewildering corkscrew combinations. The surface is mainly sand, which distorts handling, until you hit a patch of 'hard pack' (compacted dirt), which suddenly gives more traction.
In motocross you race around the circuit at breakneck speed with 30 or 40 other riders. The race lasts for an exhausting 25 minutes plus two laps. Most riders are gentlemanly enough not to ride over another who has fallen, but generally there are no rules. On a sunny winter morning, Bradley stood in the centre of the course on a 10-metre high hill, surveying the progress of Mark Farrelly, who had come from Ireland with his mechanic in a motor-home to compete. Farrelly took the berms like a speedway rider, kicking up a shower of grit, came off the leaps to fly several metres through the air, and showed perfect technique in skipping between consecutive bumps so that his front wheel landed bang on top of each one. 'He kicks up a lot of roost (dirt) coming out of the turns,' Bradley said admiringly. 'And he keeps the front wheel light.'
It looks easy, and the average lap speeds of 30 mph may seem low, but motocross is full of surprises. For a start, the old cliche that the machine is an extension of the person operating it is reversed - you ride standing up most of the time, using your arms and legs as shock absorbers. This is where mountain bike training helps so much, as a good strong motocross rider can control the back end of the 100 kg motorbike with his thighs.
The sensation, as the Kawasaki KX250 pulled away down the straight, was rather like waterskiing: most of the time you're just hanging on for dear life. The modest engines are perfect for the job, being light but still powerful enough to deliver incredible 'bottom end'. In second gear you can lift yourself out of a wet sandy rut and up a 40- degree hill in an instant. Coming down the other side is something else again. But this is the sort of sport where you accelerate out of trouble. Like on a roller-coaster ride, you're paying for the sensation of being always on the verge of losing control.
Motocross bikes are built for abusing. They look like giant grasshoppers, with all unnecessary mass removed - no lights, mirrors, a small tank - but you're allowed to treat them worse than insects: the clutch is only used to get into first gear, after that, you just stamp the thing into gear with a satisfying crunch.
The rule that on bikes, slower is harder work, is overturned. 'The faster you go, the more of your body you use,' Bradley explained. 'You can say that again,' Farrelly chipped in, removing his helmet and grinning.
Information: The Auto-Cycle Union, ACU House, Wood St, Rugby, CV21 2YX (0788 540519)