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Old 04-21-2008, 04:37 AM   #8 (permalink)
Bearleener
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Location: Berlin, Germany
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Cars compared in wind tunnel

Quote:
Originally Posted by Dradus View Post
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?
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.
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