Need Help Calculating MPH Increase From Reduction in Drag Coefficient

Click For Summary

Discussion Overview

The discussion revolves around calculating the increase in maximum speed of an electric motorcycle resulting from a reduction in the drag coefficient. Participants explore aerodynamic parameters, gear ratios, and motor specifications, focusing on the interplay between speed, drag, and power requirements.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • One participant expresses a need for assistance in incorporating aerodynamic calculations into a spreadsheet for maximum speed, specifically aiming for a drag coefficient of 0.37 or lower.
  • Another participant argues that maximum speed is primarily determined by the motor's continuous speed rather than aerodynamic factors, citing a specific power requirement formula for overcoming drag.
  • There is a suggestion that increasing maximum speed could involve changing tire size, gear ratios, or using a larger motor, with a focus on balancing speed and driving range.
  • A calculator is recommended to determine maximum speed based on aerodynamic parameters, providing specific values for a motorcycle's configuration.
  • A later reply discusses the implications of changing gear ratios on cruising speed and torque requirements at lower speeds, noting the reduced aerodynamic benefits at those speeds.

Areas of Agreement / Disagreement

Participants express differing views on the factors influencing maximum speed, with some emphasizing the role of aerodynamics while others prioritize motor specifications. The discussion remains unresolved regarding the optimal approach to balancing speed and efficiency.

Contextual Notes

Participants mention specific values and parameters (e.g., CdA, weight, power) but do not fully resolve the assumptions or dependencies related to these calculations. The discussion includes various approaches without a definitive conclusion on the best method to achieve the desired speed increase.

Animag771
Messages
12
Reaction score
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
 

Attachments

Engineering news on Phys.org
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.
 
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.
 
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.
 
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).
 
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...
 

Similar threads

  • · Replies 16 ·
Replies
16
Views
4K
  • · Replies 5 ·
Replies
5
Views
6K
  • · Replies 16 ·
Replies
16
Views
8K
  • · Replies 4 ·
Replies
4
Views
2K
  • · Replies 4 ·
Replies
4
Views
4K
  • · Replies 6 ·
Replies
6
Views
4K
  • · Replies 3 ·
Replies
3
Views
9K
  • · Replies 1 ·
Replies
1
Views
3K
  • · Replies 7 ·
Replies
7
Views
5K
  • · Replies 1 ·
Replies
1
Views
7K