Quote:
Originally Posted by aesthetect
i did the calculations before for a chevy equinox (it was for a hybrid electric vehicle design competition so 0-60 time and vehicle weight were the design variables). i dont have all the values needed to do it for a 1er but really if you change the mass, Cd and frontal area its close enough. these are the values of the forces acting on that vehicle at 140mph (where drag is at peak)..
mass: 1536kg
inertial mass factor: 1.05 (this keeps us from having to do sloppy dynamics)
Cd: 0.33
Af: 1.86 m^2
Tire rolling resistant coefficient (this should be more, this value is for low rr tires found on hybrid project cars etc) = 0.01
rolling resistance force (mass*gravity*Crr) = 150.7 N
aerodynamic drag force (what weve been talking about) = 1442.7 N
inertial force (m*Imf*acceleration) is a bit trickier because we have to account for rate of acceleration. i used the times from the C&D test
fitted to the simplified nonlinear relationship v=Vm(t/tm)^z
where Vm=60mph and tm=4.7s(as tested) approximated the z value to be around 0.5 (gives a 25.6 0-140 time). the average acceleration during the last second using that model is about 2.76 m/s^2. thus..
inertial force = 4451.3 N
this sounds unreasonably huge inertial force but assuming a wheel radius of 0.34m this comes out to a required torque of 361lb/ft. which is a bit much if we can theoretically get to 150mph, but i dont think i need to tell you my model isnt perfect.
so, what have we learned?
if the car is going at constant velocity, yes, 90% of the forces acting on the car are from aerodynamic drag (fuckin spot on, actually). but if we are trying to accelerate in any way, that takes a hell of a lot more effort than anything else involved.
i really should have spent that 30 minutes on my thesis.
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I find no flaw with your work. I was just too lazy to do it all myself:biggrin: Now get to work on your thesis!