Speed/acceleration calculations for an Electric motorcycle

  • #1
Good day all,

This is my first post here, hope you all are able to help me out here.

I am thinking about converting an old Suzuki GS500E from an internal combustion engine to an electric motor.
At the moment I am having some difficulties with the physics side of things, I would like to calculate the acceleration of the bike with a given amount of torque, given size of wheels and weight of the bike (all the info from the electric motor that I had in mind is also available of course).
Could someone walk me though the process of how this should be done?

I used to have physics in high school, but that's a few years ago and I don't seem to recall it all very well.

Please let me know which information is needed and I'll do my very best to supply everything that is needed.

Awaiting your responses,

Kind regards,


Answers and Replies

  • #2
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Adjusting torque for any transmission transformations you will find that the torque supplied to the wheel determines the force that the wheel supplies to/from the ground under acceleration. Torque = tangential force times radius so force = torque/ radius. Then you apply Newton's law F=mA to get the acceleration of the bike as the force divided by mass.

If you are dealing with any gears, or belts or such, then convert torque to force using the radius of the belt pulley or gear or sprocket and then converting back using the radius of the other gear or sprocket or belt pulley. If you have a 'black box' transmission then you can count on the torque ratio being the reciprocal of the turn ratio (you always trade off force for distance with levers and torque for rotation amount with gears).
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  • #3
Hi Jambaugh,

Thank you for your reply.

The torque is 33,3 Nm, the radius of the wheel is 0,33 meter, so this should give a force 100,9 N.
The bike itself is 250KG, so this should give an acceleration of 0,4 m/s2, correct?

I assume this is not taking into account the gearing ratios as you said.
Would you be able to give me some guidelines on doing these calculations with gears included?
The gear ratio I am thinking about is 4,55:1 (11 teeth front / 50 teeth back).

Let me know if you need any additional information, and again thank you for your help :).

EDIT: 11 teeth sprocket = 81,3mm diameter & 50 teeth sprocket = 253mm diameter.

I've been doing the calculations myself, but would like to have someone check it for me.
Force = torque / radius, 33.3 / 0.02815 (11T front sprocket radius) = 1.182 N
1.182 N * 0.164 (65T back sprocket radius) = 193,85 Nm on back sprocket
193,85 / 0.306 (back wheel radius) = 633,5 N
633,5 /250 KG = 2,53m/s2.

Is this correct?
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  • #4
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Don't forget to add the mass of the rider. 90kilos for an adult male? Or has that already been figured in?

Your calculations appear valid. From where to measure the radius of a sprocket can be an issue. It needs to be from the point of contact with the chain or gear. It's better to use the gear ratio. so multiply supplied torque by 50/11.

If you want a 0 to 60mph or 0 to 100kph convert 100kph to 27.777... m/s. Divide that by your acceleration you get 0 to 100kph in about 11 seconds with your value. Not a drag racer but it'll get you there.
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  • #5
What is the max RPM of the DC motor ?