The Big Picture
in [Racing]
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From: Dirt on 17 Sep 2009 13:21 On Sep 17, 9:33 am, Mark N <menusbaumNYETS...(a)earthlink.net> wrote: > It's just very strange, one assumes fundamentally a chassis problem but > tied in with how the bike makes power and how the electronics manage it. > Here is a comment by Stoner way back in November of '06 after a test at > Jerez: "Today we focussed on the engine to help smooth out the harsh > power delivery under acceleration at the rear." That sounds eerily like > the pumping problem that Hayden has complained of this year, I think the > most specific he's been. In any case, it will be interesting to see if > Hayden can managed to help them find and fix the problem... There was a story on Motorcycle Daily (link below) that suggests Hayden and his crew have done nothing more revolutionary than raise the center of gravity of the bike to increase weight transfer. The theory being that an extremely low COG has prevented sufficient weight transfer to allow the tires to heat up for anyone but Stoner. Motorcycle Daily -- "A low center of gravity is generally considered a good thing on a race bike, but Ducati indicates that raising the center of gravity (by raising the seat height and the handlebar height) on Nicky Hayden's Desmosedici has made the machine much more rideable, and consistent. How? By heating the tires more quickly, and consistently." Motorcycle Daily -- "The higher center of gravity allows the bike to dive more on the brakes and squat more under acceleration -- typically considered negative behavior from a racing motorcycle, but apparently necessary to warm the tires more quickly for mortal riders like Hayden and Melandri (Casey Stoner is so hard on the gas from the start, he has no problem bringing the tires up to temperature, quickly)." I'd wager there's merit in that theory but I'd also find it difficult to believe it's that simple a fix. http://www.motorcycledaily.com/15september09_desmomystery.htm
From: pablo on 17 Sep 2009 13:29 On Sep 16, 3:23 pm, sturd <mikesturdevant...(a)hotmail.com> wrote: > Julian Bond notes: > > > There's another one that old LC owners will understand. They're more > > fun! A ZX6R-B1 or a recent R6 is enormous fun precisely because it's got > > a powerband and it needs its neck wringing. > > Riding on the limit is where it's at. I'm hestitant to believe that > even a decent club racer can ride an R6 at the limit. I have more fun wringing the hell out of a little cross bike turned into a supermoto (and broke a bone for the first time in over 20 years, damn my eagerness on that little thing) than having a hypercapable bike get bored underneath me, reminding me all the time how far away I am from riding it at the limit. A few weekend ago I rode a friends shiny new Yamaha R1, the Rossi edition big bang, and had a blast, but it was just too... too everything. We then traded bikes again, and I rode a 20 year old Guzzi Le Mans, and while it was quite flawed in direct comparison it was more fun, I'd say.
From: Dirt on 17 Sep 2009 14:44 On Sep 16, 1:18 pm, pablo <pa...(a)simplyhombre.net> wrote: > I think you underestimate the development that happens from year to > year, and the fact the 1000cc's themselves would naturally get faster > aorund corners, too. That is a development priority. So I think > cornering speeds get faster no mater what. It was not because it was > an 800. It was because of development that would benefit a 1000cc too. There's valid reason behind the notion that nothing more than a reduction in engine size will enable a bike to go around corners faster. I don't understand it fully, so I'll keep it simple as much for my own explanation as anything, but... The rotational inertia of a system can be roughly described as: I = k * m * r^2 Where: I = moment of inertial k = a constant m = mass r = the radius of the object The constant "k" is related to the object's shape and will remain the same. I'll make a couple of assumptions, again for the sake of simplicity. One is that the mass of the 990 and the 800 rotating components remains constant. The other is that the bore/stroke ratio remains constant between the two motors. What I found is that a 20% reduction in capacity equates to a 12% reduction in rotating inertia with the constraints above. If you can achieve a 10% mass reduction in the 800 cc motor (which I think is realistic), then the rotating inertia is reduced by almost 22% compared to the original 990 cc motor. A 22% reduction in rotating inertia is substantial. I don't know if you've ever done the high school science experiment in which you try to change the direction of a rotating bicycle wheel while holding each end of the axle, but I assure you it's not easy. The force that is no longer required to change the direction of the motor within the chassis is now available for side grip. The overall rotating inertia of the motorcycle won't go down that much (engine, wheels, chain, etc) but it's reasonable to assume that a simple engine mass reduction will allow a corresponding increase in corner speed because there's less resistance to the directional change. -Dirt-
From: Dirt on 17 Sep 2009 15:17 Taking it a step further, if the motor is perfectly scaled down 20% from the 990 to the 800, including a 20% mass reduction, you realize a full 30% reduction in rotating inertia. An as an interesting aside, I tried varying the bore/stroke ratio and it had absolutely no effect on the inertia reduction so long as it remained constant between motors. -Dirt-
From: Mark N on 17 Sep 2009 15:30
On Sep 17, 10:21 am, Dirt <christopher.l.ca...(a)gmail.com> wrote: > There was a story on Motorcycle Daily (link below) that suggests > Hayden and his crew have done nothing more revolutionary than raise > the center of gravity of the bike to increase weight transfer. The > theory being that an extremely low COG has prevented sufficient weight > transfer to allow the tires to heat up for anyone but Stoner. > > I'd wager there's merit in that theory but I'd also find it difficult > to believe it's that simple a fix. Yeah, I've heard about the tire temperature thing, and I have a hard time buying that's remotely what the whole issue has been. If that was the case I'd think we's see times that Hayden is faster, almost as fast as Stoner, where the tires happen to be operating at optimum, and we'd also see him much closer when running softer tires, certainly last year with Melandri when there were many more tire options, and that hasn't been the case. I'd also think there would be times when Casey is really struggling, because even he wasn't getting enough heat into the tires. And one would think that the tire technicians would know what was happening, even if they didn't know why. It just seems more like a bandaid approach to a larger problem. |