I’ve developed a web calculator that may help people select a drive train for a conversion.

EV Calculator
It will predict the speed of a car for different power levels, taking into account rolling resistance, aerodynamic resistance, and gravity if you’re driving on a grade. This was easy for me to create, since I’ve had similar calculators for nerdy cyclists on the web for over 20 years. There are parameters to input that you may not know very well - those are the major sources of error.

Wait! I’ve not included any efficiency figures - use your own judgement to account for driveline loss, electrical loss, and the effects of ancillary equipment. Perhaps those effects can be incorporated into the next version.

The staring values you find are for my own project: a Jaguar Mark 10. As an example, there are values for a Zonic 120 motor fitted to a 1.9:1 reduction gear coupled to a central driveshaft.

Given inputs for your gear ratio, differential ratio and tire diameter, the RPM of your motor will be correctly displayed.

The lower section predicts acceleration to 60 mph or 100 kph. This uses an approximation of a motor’s torque curve, so you only need to input four quantities.

That’s the gist of it. There’s much more to read on the calculator page. Check it out, let me know what you think.