Motor Cycling: Dangerous lure of the island race: Mac McDiarmid looks ahead to a week of high endeavour at the Isle of Man TT races

SHORTLY before sunrise tomorrow morning, practice begins for one of the most compelling anachronisms in sport. After five gruelling days of testing, the Isle of Man TT begins in earnest on Saturday when the first 750cc motorcycle hurtles down Glencrutchery Road in suburban Douglas, through the traffic lights at St Ninian's crossroads, and plummets down Bray Hill. Racing ends six days later with the blue riband Senior race.

In between, 320 riders from 19 countries will have completed 200,000 practice and racing miles, and most of them will have done so at their own expense. Any rider dominating the week's proceedings stands to win, at most, around pounds 20,000 - or one tenth as much Stephen Hendry pocketed at the Crucible last month. It is one of the most dangerous sports known to man, there are no world titles at stake, and little sponsorship or public recognition. Why do they do it?

Scotland's Steve Hislop, the 'Flying Haggis', the fastest man ever around the island and the favourite for this year's two major races, is in no doubts. 'It's still one of the greatest challenges in the world,' he said. The challenge derives from a 37.73 mile course on closed public roads, with over 250 interlocking corners, bumps beyond counting and cambers of alpine proportions. It reputedly takes three years to learn, and no man knows it better than Joey Dunlop, the veteran Ulsterman who last year chalked up his 15th TT win, more than any man in history.

At a time when tragedies in grand prix racing have brought the risks involved in motor sport into sharper focus than ever before, motorcycle road racing lives with a simple truth. However many helicopters are laid on, however good the medical facilities, TT racing is dangerous. Fatalities will occur - maybe not this year, maybe not next, but the one after that.

Twenty years ago, the TT races were stripped of their world championship status. The event has since become increasingly marginalised to a band of mainly British and Irish specialists. But to the 40,000 or so fans who flock to the races, they are the only 'real' road racers: the rest are pampered stunt riders. To the riders themselves, whether fast or slow, nothing compares with pitting yourself against this pitiless circuit.

There is also fear, as Hislop explains: 'The place scares me. I think it scares most riders, if they're honest. The speed you're travelling . . . the thought of a mechanical failure is always in the back of your mind, yet almost too frightening to contemplate.'

It is a challenge, too, for the machinery - which is precisely why racing, on two wheels and four, began on the island 90 years ago. Any racing machine surviving a six-lap TT race has proved itself beyond question. This is why an astonishing device designed and built by one man in Christchurch, New Zealand, will attract more interest than any other this year.

The Britten, built by the eponymous genius, John Britten, is a 1000cc V-twin housed in a revolutionary chassis. Last year, in a debut plagued by mechanical problems, it established itself as the quickest machine through the speed trap before breaking down while lying in eighth place.

This year there will be three Brittens, each ridden by top-class TT specialists; Nick Jefferies, last year's Formula One winner, will team up with Ireland's Mark Farmer and Kiwi Robert Holden. This trio will provide the toughest challenge to the Castrol Honda RC45s of Hislop, Dunlop and Phillip McCallen. The Hondas, although new this year and unproven on public road circuits, rely on traditional technology and should go well. Hondas have won every one of the last 12 Formula One TT races. For the world's biggest motorcycle manufacturer to be defeated by the home-built Britten would be a disaster for the Japanese.