Here ya go.... I wrote this a long time ago... the topic is below http://www.bimmerwerkz.com/forum/index.php...76&#entry166576
This is only showing how much HP differs with differen rotational mass...
Moment of Inertia - The property of an object associated with its resistance to rotation. It depends on the objects mass and the distribution of mass with respect to the axis of rotation.
Basic Rotational Inertia formula. I= ½ MR2 (2 = squared)
I= Moment of Inertia... M = mass and R = radius of the wheel.
So... lets take a 20 pound wheel... 17 inch.. (I'll work in SI units)
I= .5x(9.0718474)x(0.4318/2)>2 (>2 means squared)
I= .959040098 kg/m>2
The same equation for a 15 pound wheel that is 17inches...
I= .539460063 kg/m>2
Just for clarity.. the next exp. is the same two wheels being pushed by 200 HP. ( Its not exactly right because I'm not taking in acount for the weight of the car.. but this should demostrate how much the weight of the wheel actually plays in acceleration of the car..)
Ok.. still speaking of a 17 in. wheel here...
Equation for torque being applied to both wheels is: Force times the Radius:
BTW 200HP is equal to 529559102.065818 Newtons
t = Fr = (529559102.065818N) x (.4318/2)= 114331810.1
This torque value is a constant... because it is just showing how much force is applied.
AND finally... when you take the Torque.. or Force being applied to each wheel.. and DIVIDE it by the moment of inertia.. which I remind you is the resistance to rotation. You get.....
20lb Wheel : I/t = (114331810.1)/(114331810.1) = 119214838.2 rad/sec>2
15lb Wheel : I/t = (.539460063)/(114331810.1 ) = 562500008.2 rad/sec>2
Ok... So.. now your wondering what the hell I've found with these numbers... well after another converstion from radians per second squared.. to RPMs... I get..
20lb Wheel : 5270.45301489 RPMs
15lb Wheel : 24867.9603047 RPMs
Both of those nubers clearly demonstrat... that with less weight you can speed that wheel up faster... an almost 2000 RPM increase due to 5 lbs of weight.
So... in short... lol... it takes
This is how much HP it takes to move each wheel....
20lb = 0.13039 horsepower
15lb = 0.07335 horsepower
As you can see... the 15lb wheel... takes less horse power to move..
All in all.. this is a sick conclusion.. to... who cares about 5 pounds.. when it comes to a cylindrical object being pushed by your engine... unless you want to gain... 0.5704 HP. Your choice...