This weekend Loris Capirossi aims to gain revenge on his four-stroke rivals after a difficult Japanese GP. Although the hard-riding Italian qualified second fastest at Suzuka he had a tougher time in the rain-affected race, finishing ninth, well behind winner Valentino Rossi.

Capirossi believes he will have a better chance at Welkom, where he has challenged for victory on his last two visits. Two years ago he finished third at the track in his comeback 500 ride and last year he was second, duelling throughout with winner Rossi. Before this season started Capirossi felt that the 500s would have little chance against the latest four-strokes but his pace during Suzuka qualifying suggests otherwise.

"I like Welkom very much, it's a good track for me and for my bike," he says. "I believe the gap between the 500s and the four-stroke will be less than at Catalunya, where we tested against the four-strokes, and at Suzuka, so I've great expectations of a good result.

"Although I'm still riding a 500, I have a much better package than last year. The new NSR is maybe 50 per cent better than the 2000 model I raced last season, it's much easier to go fast with this bike. I'm one second faster than last year at most tracks, easy! The balance is better and it uses its tyres less. Also, the new tyres we have from Michelin are a big improvement. We are using the same 16.5in rears that the four-stroke guys use and these tyres have more grip, they're more consistent and they make the bike more stable, so it moves around less. They are another step on from the 16.5s we started using last year.

"Welkom is very tough on tyres because the weather is usually hot and because there's a lot of bumps and the track is quite slippery. But I love the place because it's got some fast corners and I love quick corners, I hate hairpins. The most important part of the track is the two corners at either end of the long back straight. Both are long and fast, so you can really make a difference if you get these right and if youčre brave. Riding through the turn that takes you on to the straight it's very important to make sure you lift the bike as much as possible, so youčre riding on the fatter part of the tyre, so therečs more rubber on the tarmac.

"The front tyre is also very important at Welkom, well, for me the front is important everywhere. I use the front very hard, and if I'm not getting any feel from the front, I can't go fast. When I go to a track I always work on the front end first, then think about the rear. I've used the same front tyre for the past two years because I was happy with that tyre but Michelin's latest fronts are better, they have more feel, and that's what I need to be fast."

Welkom works tyres much harder than Suzuka, with rear slicks running at around 20 degrees hotter than at the Japanese track. This is why the South African circuit is the biggest challenge of the Grand Prix year for Michelin's engineers.

"Welkom and Phillip Island are the toughest circuits on tyres, though Phillip Island only really works the rear," reveals Michelin Grand Prix manager Emmanuel Fournier. "Even the front has to work very hard at Welkom, running at a very high temperature.

"The circuit is difficult for many reasons: it's slippery, it's bumpy, it has some very fast corners, plus it's usually very hot and dusty there. So we use hard constructions for both tyres because you dončt want too much heat getting into them."

The corners that place the biggest demands on tyres are the two high-speed rights near the end of the lap. These ask a great deal from the rear, with riders laid over for several seconds at 200kmh, controlling wheelspin on the throttle. Much is also demanded of the front, because the bumps and lack of grip cause front-end to push as riders dive into turns. That's to say the tyre is on the verge of breaking traction, driving a serious amount of heat into the rubber and carcass.

"Of course, we have new fronts and rears this year, so it'll be very interesting to see how they work, both with the four-strokes and the two-strokes," adds Fournier. "Our new front gives more feel, which is exactly what riders need at Welkom. So far nearly all our riders are now using this tyre ­ it takes time for riders to get confident in a new style of front.

"We've done a lot of work on fronts, but front tyre choice is a very subjective thing for riders. Many riders are quite conservative with their front tyres because they want a tyre with which they're very familiar. Rossi, for example, has been very happy with the new front we produced at the end of 2001, though he also likes a couple of new construction fronts he has tested over the winter, so he has three to choose from. Valentino is one of those rare riders who can be very fast with several different solutions."

"Our new 16.5in rear was designed to give a bigger contact patch to handle the four-stroke's extra power output but has also proved very useful for our 500 riders. We've produced various different profiles over the last six months or so, but we're really only using one of those profiles now, the one which we first tried during HRC's Jerez tests last November."