Rossi’s big bang theory
Stopwatch never lies. That may be true but it doesn’t always tell the whole truth. That, at least, is what Valentino Rossi must have been telling himself after his much anticipated Ducati debut in early November (above). After two days of testing aboard the factory’s Desmosedici MotoGP bike at Valencia he was 15th fastest, 1.7 seconds off the pace. Oh dear.
Rossi isn’t allowed to tell the world what he thinks of the Ducati, because although Yamaha granted him early release from his contract they banned him from discussing his new bike in public. But it is unlikely he is really worried.
This was a shakedown test, aimed at using Rossi’s remarkable abilities as a development rider to give Ducati engineers a direction in which to work during the 11-week winter testing moratorium. A damaged shoulder also slowed him. Straight after the tests he returned to Italy to undergo surgery on the injury, the legacy of a fall in a charity motocross event last April. Last season the tendon damage sustained in that low-speed fall troubled him more than the broken leg he suffered in a horrible 110mph crash at Mugello.
The big question Ducati wanted answered in Spain was which way they should go with engine configuration. Rossi evaluated two versions of the Desmosedici V4 with different firing configurations the so-called ‘screamer’ and ‘big bang’. The fact he started out at Yamaha doing exactly the same job gives some indication of the crucial nature of combustion timing in motorcycle racing.
The screamer and the big bang use differently timed crankshafts: the screamer fires evenly, the big bang fires unevenly with pairs of pistons firing within a few degrees of each other hence the nickname. The aural result is a sonorous groaner of an engine, compared to the higher-pitched screamer which sends shivers down your spine every time it rockets past.
On track the big bang’s result is more rider-friendly performance, with improved feel and traction during acceleration. Remarkably, no one is quite sure why. One theory suggests that grouping the power pulses together allows the rear tyre to regain grip between each salvo. Another proposes that the big bang exorcises ‘inertia torque’, the effect of the crankshaft decelerating and accelerating during each stroke, which spoils the rider’s feel for what’s going on at the rear tyre.
Even Ducati’s genius chief engineer Filippo Preziosi admits he doesn’t have all the answers: “We have numbers that show the big bang has some advantages and numbers that show the other configuration is better in other areas. But these numbers don’t show the whole truth. From the work we do on the test bench we have less than 50 per cent of the truth, the rest comes from the rider.”
Following Rossi’s input at Valencia Preziosi seems likely to take the big bang road, which is the same road Rossi chose when he started with Yamaha in 2004 and the same road Casey Stoner chose during his time with Ducati.
The unevenly timed crankshaft does cost a little in terms of pure horsepower but that’s irrelevant because the screamer’s power is so difficult to put to the ground. “The last time I tried the screamer it wanted to rip my arms off and spin up and buck and weave,” says Stoner. “I wanted nothing more to do with it.”
No one knows whether Rossi will win on the big bang Ducati, not even the man himself, which is perhaps why he wore a question mark on his helmet at Valencia. However, Rossi’s faithful crew chief Jeremy Burgess who followed him from Honda to Yamaha and now to Ducati is convinced that this will be another successful venture: “That is without question. We’ve done it before: we did it when we went from two-stroke to four-stroke (in 2002), when we went from Honda to Yamaha, and when we went from 990cc MotoGP bikes to 800s, and now we’re a bit older and wiser.”
The stopwatch will next pass judgement on Rossi and his 2011 rivals at Sepang in early February.