Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Automotive Need Help Calculating MPH Increase From Reduction in Drag Coefficient

  1. Oct 30, 2012 #1
    I am new to the forums and need help with something. I have been using a spreadsheet that somebody else made in order to help me design an electric motorcycle. I have been inputing my own data using most of his calculations and I have noticed that he did not calculate any aerodynamic parameters when into the formula for max speed. I have no idea how to do that, so I need the help of anybody who is willing. I have attached the spreadsheet.

    Thanks,
    Andrew
     

    Attached Files:

  2. jcsd
  3. Oct 30, 2012 #2
    P.S. I am looking to get my drag coefficient down to 0.37 or lower, but I would like to be able to input the formula into the Max Speed cell (K28) so that when I change values in the spreadsheet it will update the calculations accordingly.
     
  4. Oct 30, 2012 #3
    By my calculations the max speed is dictated by the maximum continuous speed of the motor, not the aero. The power required to overcome drag is given by 1/2*p*V^3*CdA. In your case of 56mph, that is just 2.6kW out of your 11.3kW motor.
     
  5. Oct 30, 2012 #4
    Ok so the only way to increase the max speed would be to increase the tire size, change the gear ratio, or get a bigger motor. Thanks. I guess I will have to change the gear ratio and use the aerodynamics to increase the driving range, because my range will go down at higher speeds without aerodynamic modifications.
     
  6. Oct 30, 2012 #5

    jack action

    User Avatar
    Science Advisor
    Gold Member

    You can use this calculator to determine your maximum speed due to aerodynamics. Theory is at the bottom of the page to find how to calculate it.

    For your motorcycle (CdA=0.25 m²; Roll. Rest.=0.02; weight=470 lb; wheel power=15 hp), it turns out to be 87 mph (with proper gearing, of course).
     
  7. Oct 31, 2012 #6
    Thank you. I will just change the gear ratio a bit so that I will have a higher cruising speed and let the aerodynamics make up for the extra battery drain and reduce the drag at higher speeds. The only concern with changing the gearing though is how much torque will be needed to move the vehicle at lower speeds, because the aerodynamic benefits will be less help at lower speeds. Though that is an unrelated topic...
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Need Help Calculating MPH Increase From Reduction in Drag Coefficient
Loading...