From: Dirt on 17 Sep 2009 15:51 On Sep 17, 2:30 pm, Mark N <menusb...(a)earthlink.net> wrote: > 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. Perhaps there's more merit to the tire load rather than the tire temperature. I've read an interview with Rossi in Roadracing World(?) where he talks about keeping the tire loaded at all times being an absolute requirement to get things to work. Perhaps this is a related extension of the changes Burgess made to Rossi's machine when they switched to Bridgestones, i.e. to keep the tires loaded and working. -Dirt-
From: Bruce Richmond on 17 Sep 2009 23:04 On Sep 17, 2:44 pm, Dirt <christopher.l.ca...(a)gmail.com> wrote: > 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... I don't think it is engine size so much as power, or power to weight. The rider experiments to find out what works best and finds that for a lower powered bike it is best not to slow down any more than you have to. The higher the cornering speed the greater the commitment of the rider to accept risk of falling in the turn. On the more powerful bike the rider has the option of slowing a bit more, cornering at reduced risk, and still getting back up to speed. The lower speeds can also translate into sharper but shorter turning. That allows it to spend more time upright where it can play its trump card of acceleration. It could quite likely corner as fast as the less powerful bike, or very close to it, but doing so would limit its acceleration leaving the turns. The more traction you are using for lateral forces the less you have left for acceleration. If the less powerful bike slows down to the same speed as the more powerful one it gets left behind in the drag race out of the turn. Bruce > 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: Julian Bond on 17 Sep 2009 19:57 Mark N <menusbaumNYETSPAM(a)earthlink.net> Thu, 17 Sep 2009 07:33:56 >Just so I'm clear on this, here is what I'm talking about: >http://www.superbikeplanet.com/2006/Nov/tb/061101e.htm Oh right. Damn near 3 years ago then. -- Julian Bond E&MSN: julian_bond at voidstar.com M: +44 (0)77 5907 2173 Webmaster: http://www.ecademy.com/ T: +44 (0)192 0412 433 Personal WebLog: http://www.voidstar.com/ skype:julian.bond?chat Speed Checked By Radar
From: Dirt on 18 Sep 2009 07:15 On Sep 17, 10:04 pm, Bruce Richmond <bsr3...(a)my-deja.com> wrote: > The higher the cornering speed the greater the commitment of the rider > to accept risk of falling in the turn. On the more powerful bike the > rider has the option of slowing a bit more, cornering at reduced risk, > and still getting back up to speed. The lower speeds can also > translate into sharper but shorter turning. That allows it to spend > more time upright where it can play its trump card of acceleration. > It could quite likely corner as fast as the less powerful bike, or > very close to it, but doing so would limit its acceleration leaving > the turns. The more traction you are using for lateral forces the > less you have left for acceleration. If the less powerful bike slows > down to the same speed as the more powerful one it gets left behind in > the drag race out of the turn. Well, you've got a point, but I still maintain that the bike with the smaller engine will be quicker into and through the corner because there's less gyroscopic effect and because it requires less physical force to tip in, less tractive force to maintain a turn and is easier to adjust mid-corner. -Dirt-
From: Mark N on 18 Sep 2009 10:17
Bruce Richmond wrote: > Dirt wrote: >> 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... > > I don't think it is engine size so much as power, or power to weight. > The rider experiments to find out what works best and finds that for a > lower powered bike it is best not to slow down any more than you have > to. > > The higher the cornering speed the greater the commitment of the rider > to accept risk of falling in the turn. On the more powerful bike the > rider has the option of slowing a bit more, cornering at reduced risk, > and still getting back up to speed. The lower speeds can also > translate into sharper but shorter turning. That allows it to spend > more time upright where it can play its trump card of acceleration. > It could quite likely corner as fast as the less powerful bike, or > very close to it, but doing so would limit its acceleration leaving > the turns. The more traction you are using for lateral forces the > less you have left for acceleration. If the less powerful bike slows > down to the same speed as the more powerful one it gets left behind in > the drag race out of the turn. The problem with this, I think, is that it would take experimentation to arrive at an approach which would result in maintaining the old lap times, and there probably would be a certain amount of crashing in that process, it seems. Plus there almost certainly would have been younger 125/250-bred riders who would have already been doing this on 990s, just because it would have been more like what they were used to. And yet what it appears we saw in late '06 was guys hopping on the bikes and at speed immediately, not really losing anything from day one, and then reporting the bikes were simply faster in the corners. That sounds like a physics difference, they went into the corners and immediately discovered they could turn the bikes more quickly, they didn't have to fight the momentum of the bike as much as they were used to. They would certainly then have to figure out how to fully optimize this change, but its impact would be felt immediately, just as an increase in displacement/power would be felt, first time they twisted the throttle. The 800s still make a huge amount of power, and guys coming from SBs would likely have continued to use an approach more like the 990s, a style also more like they used in SB, where the power was similar to or less than the 800s, but they really didn't, they were also cornering fast enough not to lose lap time, and right away. |