Quote:
Originally Posted by Dradus
Yeah, I was surprised too, thats 220lbs per .01 of Cd. Thats a huge savings when you look at it like that, especially when you're building a lead acid EV conversion.
Is there any data out there showing different weight reduction equivalents?
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It didn't say in the article, but I'm guessing they meant the rolling resistance at constant speed, which is proportional to the weight, and not accelerating and braking, where weight has a greater effect on fuel economy.
Back-of-the-envelope calculation (similar to Mercedes E200 @ 100 km/h):
Aerodynamic drag Fa = (1/2)*Cd*A*rho*v^2
= (1/2)*0.29*2.22*1.21*(100/3.6)^2 = 301 N
Reducing Cd to 0.28 would reduce Fa by 10.4 N
Rolling resistance Frr = Crr*W = Crr*m*g
= 0.01*1600*9.81 = 157 N
Reducing weight by 100 kg would reduce Frr by 9.8 N
Yup, that fits! So this weight equivalent applies only to constant-speed cruising. In the city weight matters much more.