In my opinion, it's two things. 1, is BSFC as Sendler already mentioned. Which is ideal for the centurion; being at the optimal engine loading in an underpowered diesel at a very aero efficient speed. When a motorcycle can be overpowered in many instances.
2, The ratio of aerodynamic resistance to vehicle mass.
The problem is a motorcycle has a great deal of aerodynamic resistance for it mass. Meaning it doesn't coast as far in "pulse and glide." Adding weight may achieve a longer coast while improving the BSFC of the pulse, netting overall better mpg. Improving aerodynamics would be the ideal solution since adding weight is only a half remedy.
Another part is momentum. Your
speed multiplied by the
mass of your vehicle. Trading Kinetic energy (speed) for potential energy (elevation) is a very efficient way to climb and descend hills. You want to use as little power ascending, and then convert your elevation back to speed at the bottom. The less mass you have, the more you rely on speed. You would need to drive faster to have enough momentum to carry you to the top of the hill. And the faster you drive the more air resistance there is!------There is an ideal weight of course,
given how aerodynamic your vehicle is. It's all a trade off. At the GGP many cars were to heavy to corner turn one at an ideal speed and thus couldn't reach the bottom with enough speed to use most of that momentum to carry them to the top of the hill climb. The centurion's light weight was ideal for the course. Once you have momentum, if you can convert it to elevation and back again (without scrubbing speed, or going too fast) it is efficient. Real world exceptions would be maintaining freeway speed up an extended hill climbs where the descent is to steep of an angle to coast efficiently down.
Which brings me to another aspect. The ratio of mass to aerodynamic resistance determines how shallow a negative grade you can coast down (in gear or in neutral). With a high drag low mass motorcycle, you need a relatively steeper grade to maintain a certain speed than you would if you added more mass to it. Adding mass to make up for the drag means you can maintain a higher continuous speed on a shallower negative grade while using no power from the engine. On the GGP track adding weight may mean you can engine off coast from the top of the back straight all the way down the shallow descent culminating at the bottom of turn one! If you didn't have the mass to maintain speed, you might have to restart the engine to get another push to keep going. It would be incorrect to say more weight is always better. But as long as you get the right ratio for the given course or route it should help. These are just the unique problem of motorcycles that aerodynamics would be the better solution to. If you can't improve aerodynamics, only adding mass, or lowering your speed will suffice.
Quote:
Originally Posted by changzuki
There is likely a limit as to how heavy you could make the bike but with different sets of real world numbers maybe we could see what the cut-off point is and possibly come up with a forumla where "X" added weight can yield "Y" gain in mpg. Also, if the extra weight is general in nature then this may be the easiest and most cost effective way to raise mpg. Would you do this in the name of science and ecomodder camaraderie'? What say you?
~CrazyJerry
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This is the formula you should concern yourself with: i = ((krMs) + (kaAsv2d)) / (gMs)
You can figure out the exact negative grade that will maintain the constant speed of your vehicle while coasting. This would be the ideal negative grade to look for in a route so you could EOC in Neutral without gaining excessive speed, or slowly loosing speed. If you know the gradient of the GGP track, you can calculate the ideal amount of mass to add to your motorcycle!
where
P = power required (in watts)
kr= rolling resistance coefficient
M = mass of bike + rider
s = speed of the bike on the road
ka= wind resistance coefficient
A = the frontal area of the bike and rider
v = speed of the bike through the air (i.e. bike speed + headwind or – tailwind)
d = air density
g = gravitational constant
i = gradient (an approximationČ)
Just for fun: this is the formula used to determine the power required to climb a grade (there are other ways to write it). (I really do think this stuff IS fun!)
http://ecomodder.com/forum/showthrea...tor-27824.html
Power = (coefficient of rolling resistance) + (aerodynamic resistance) + (road grade x mass x speed, ie the amount you fight gravity!) *likewise how much energy gravity can give you.
P = (krMs) + (kaAsv2d) + (giMs)