After one practice session at Motorland Aragon in Spain, Valentino Rossi was eighth-quickest on Ducati’s latest attempt to give him and teammate Nicky Hayden more front-end feedback. Two years ago, Ducati adopted a new design direction, abandoning its traditional steel-tube “trellis” chassis in favor of a new Vincent-like construction using carbon fiber. In this new scheme, the engine became the main structural member, with swingarm and rear-suspension linkage attaching directly and only to it. Joining the steering head to the engine Vee in front was a pyramidal black box of carbon fiber that also performed the function of engine airbox. This construction would save considerable weight.
During his time as a Ducati factory rider, Casey Stoner (now leading the championship on a Repsol Honda) had said that on the trellis chassis, he could not “hit the same point on the track two laps in a row.” As Stoner had been world champion on such a chassis in 2007, this suggested that although its flexibility gave it good front-end “feel” (that is, it gave warning as the front tire neared the limit of its grip), flexibility in other directions made steering imprecise. This movement had also prevented Ducati engineers from sliding the engine as far forward as they would like, because during braking, the front tire would be deflected to the rear, threatening to rub on the cambox of the front cylinders. The greater stiffness of carbon fiber would prevent much of this flexure, allowing a more forward engine location.
When the carbon bike was raced, Stoner found it unpredictable. He said of it that, “You push, and it’s okay. You push some more, and it’s still okay. Then you push again and you’re in the gravel—no warning.”
The flexure of a normal front end acts like a short-travel suspension when the bike is leaned over, keeping the tire in contact with small irregularities and able to recover grip after skipping over the top of a slightly bigger irregularity. But if you take that flexure away and then hit that bigger irregularity, your front tire just hops into space and goes away, dumping you into the gravel.
Yamaha’s YZR-M1 had this same syndrome in 2003. Riders were falling because the bike was not giving them the feedback they needed to know how close they were to the limit of front grip. If you are camping on the rim of the Grand Canyon, do you get up in the dark of night to go for a walk? No, because nothing can tell you how close you are to the edge. This is why both of Ducati’s current riders, Rossi and Hayden, have spent most of this season well back from the edge in disappointing positions like the eighth and seventh spots they occupied on Friday.
Well, how about “just goin’ for it?” I mean, these guys are racers, right? Yes, but they aren’t stupid. There is no glory in crashing a bunch of priceless GP bikes. Okay, but didn’t Stoner win races on it, even if he didn’t take the championship? Yes, but his riding style has the versatility to take some pressure off the front by steering with the back.
So far, Ducati has tried variations in the design of the carbon-fiber box, adding bits of flexibility where possible by moving the front-wheel bearings closer to each other and changing steering-head bearings from rollers to balls. Ball bearings are quite elastic, as even hard steel deforms under pressure. The initial point contacts of the balls on the races become bigger and bigger circular contacts as load is applied.
Rossi’s crew chief, Jeremy Burgess, has noted that in the 10-inch length of Ducati’s rigid carbon-fiber box, it is next to impossible to design in much lateral flexibility. That requires something a lot closer to the twin aluminum chassis beams used by all other teams. Such beams, being deeper than they are thick, are able to flex laterally somewhat without allowing the steering head to twist or bend. Therefore, this weekend, Rossi is testing a bike built around this idea. In photographs, you can see something like aluminum side beams extending up toward the steering head. These would presumably attach to existing hard points on the engine but are far enough back to allow the desired lateral flexure of the beams.
Why is Rossi still in eighth if this test chassis (made by FTR in England) is so hot? The chassis has been in Ducati’s hands for roughly a week, and finding a setup takes more than an hour.
Ducati’s second problem—its rearward weight bias, making it hard to finish the corner—is another matter.
Valentino Rossi qualified 13th for Sunday's MotoGP race at Motorland Aragon, but the 32-year-old Italian will start from pit lane, 10 seconds behind the field, the penalty for having exceeded the series' "engine-durability" rule. Each rider is allowed six engines per season.
