Mat Oxley

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TAMING THE DESMOSEDICI

Only Valentino Rossi’s most ardent fans expected him to start his association with Ducati covered in glory. In 2004 the Italian turned Yamaha’s mid-grid YZR-M1 into a winner almost overnight. The fact he isn’t repeating that miracle has destroyed the myth he is some kind of motor sport King Midas.

“It is clear now that Valentino is human,” says his former Yamaha team-mate Carlos Checa. “He’s a good rider, but he doesn’t have some magic that makes any bike go fast immediately.”

Ducati’s Desmosedici MotoGP machine isn’t just any bike. It is a fearsome and frustrating motorcycle that has befuddled several World Champions. Only Casey Stoner has mastered the Italian machine, and Rossi is determined that it mustn’t defeat him.

Rossi says the problem is poor mid-corner turning, causing him to lose speed and run wide. Stoner used his dirt-track skills to ride around the Ducati’s understeer, with a combination of rear brake and throttle skewing the bike mid-corner. Rossi says he could do that (I’m not so sure he didn’t grow up riding sideways like Stoner), but it’s too risky, an opinion borne out by Stoner’s win/crash ratio.

Ducati has a new version of its unique carbon-chassis on the way, with reduced lateral flex. This ‘softer’ chassis should improve mid-corner performance, doing the job that suspension cannot do at full lean, about 65 degrees from the vertical.

But Rossi’s crew chief Jeremy Burgess believes the chassis may not be wholly to blame for the bike’s misbehaviour. He thinks the root of the problem may lie within the engine. “I’ve learnt engine character plays a huge part in how a bike handles,” he says.

Burgess may be alluding specifically to crankshaft configuration. In a motorcycle, crankshaft mass can have a crucial effect on machine behaviour, and a heavier crankshaft might be what the Ducati’s engine needs. Until now engineers have done their best to tame the engine’s dark side with electronics, but many would argue you can’t mask a hardware problem with a software fix.

Rossi is keen to soften power at the first touch of the throttle, a critical moment in racing when the rider uses the merest whiff of gas to complete the turn and ready the machine for acceleration. Part throttle is a major issue in bikes, because there’s not enough rubber on the road for big throttle openings from the apex.

“We work very much on this point,” affirms Rossi who knows a millisecond gained here can gain a tenth down the next straight. “The main problem at Ducati is that they always work on maximum performance, but not on the details which to me are important.”

Rossi already knows that increasing crankshaft mass works because he ran a heavier flywheel on his title-winning Honda RC211V to damp down the initial kick.

Crankshaft rotation is also important in bikes, affecting handling and steering through gyroscopic precession and torque reaction. This might be something else for Ducati to look at. The Desmosedici engine turns forward (with the wheels), while Yamaha’s YZR-M1 turns backwards. A motorcycle with a forward-turning crank will be more stable and thus more difficult to steer. One with a backward-rotating crank requires an extra countershaft which steals horsepower but pays back with better turning because the machine is more gyroscopically neutral. No wonder the Ducati is renowned for its speed; the Yamaha for its sweet handling.

Crankshaft rotation was an even bigger consideration in the days of the peaky 500cc two-strokes. Yamaha ran a V4 500 that was effectively two parallel twins geared together, with counterrotating cranks cancelling each other out to achieve neutral steering. Honda’s V4 used a single crank and was faster but notorious for its evil handling wide-eyed NSR riders would speak of “single-crank voodoo”. Honda tried to calm things down by fitting tungsten plugs in the crank. Finally it turned the crank backwards. The NSR lost some power but was immediately friendlier. Like everything in racing, you win some, you lose some.

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