Calculate DC motor specifications (torque power etc) for electric vehicle

Dear Sir/Madam,

I want to make an electric car like as shown in figure below., with a DC motor. assume no inclination, road is plain surface. please explain all calculation with formulas.THANK YOU
following is the basic known parameters:

Total mass of car(including rider and everything) = 250kg
initial velocity of car = 0 (still car stop)
max velocity = 60 km per hour
time to reach max velocity = 1 minute = 60 seconds
radius of tyre = 8 inch

please tell me how could i find the following parameters to find accurate DC motor for my car:

how to calculate force needed by my car?
how to calculate torque needed by my car?
how to calculate speed RPM of a motor needed by my car?
how to calculate power (watt) of motor needed by my car?
how to calculate battery needed by my car to travel 10 km in one charge?

sort by: active | newest | oldest
jaynil0074 months ago

1-you need 30NM torque for pulling you car because 1NM=10kg-cm force so on you car it will 300kg-cm force

2-in you case speed 8inch=20.32cm . tyer lagth = 2*pai*r=127.6cm

total distance in houre 60km=6000000cm

RPM of tyer need =6000000/127.6*60(houre to minit)=783.6RPM

3- power RPM*NM/9.55= power in watt 783.6*30/9.55=2461 watt

4-RANG with 2461 watt/houre battery pack you can go 60km

for 10km rang you need only410watt/houre battery pack

jitendra110 months ago

i am making a solar car and its weight is 100 kgs and adding human weight upto 200kgs. total 300kgs .

which type of motor should i use for this car .

Vinayak9122 years ago

13ft width bar want to travel from one point to another end 72ft distance.

Wheel dia- 200mm want to cover distance in 1min

fawad_pappi (author) 2 years ago

250 kgnot much...
no one is helping me

as far as i study.. that..

mass = weight of my car including rider and everything = 250 kg

accel = change in velocity per change in time...

i want max speed =60 km/h

time to reach max speed=60 sec.

so according to formula..

a=deltav / delta t

we can culaculate a with the above data and formula

then it is the torque...

torque = Force x radius of wheel

am i going right ???

your assumptions are right BUT reality is far removed from a perfect formula, You need something that will run at 800 to 1000 watts to be realistic and get what you want.

Look at the links I offered and what other people are doing rather than try to make calculatoions that won't really lead you anywhere.

fawad_pappi (author)  rickharris2 years ago

Sir rickharris,

i really appreciate your help and time, and ive seen so much helping replies of your to all ,. i thank you so much for your help,.

sir, please have a look at this webpage:


wat do you think about this?

im not getting much help from internet, please help in calculating this real life problem

rickharris2 years ago


This question one way or another comes up often - try a search for lots of information both in answers and in instructable projects. - see the related column on the right as well.

how to calculate force needed by my car?

This is really hard to do in exact terms. You can only get a real idea by comparison. the car I linked to above was around 250 pounds with driver and battery. So weight has a bigger effect than all other parameters. Followed by aerodynamic drag.

how to calculate torque needed by my car?

See above.

how to calculate speed RPM of a motor needed by my car?

In general small DC motors will have a peak torque at a given RPM - Often 2000 or 3000 RPM. You will need to consider gearing to suite your needs, Start from stationary (assumed under electric power,) top speed, Range. You may need to consider a gear box offering a range of gears, Bicycle parts are lightweight operate in the speed range your looking at and are reasonably low cost.

how to calculate power (watt) of motor needed by my car?

This depend much on how your motor has been rated. Many small DC motors are quoted at peak wattage which is fairly meaningless, best is a continuous rating which with care you can exceed.

Out motor was spec'ed at 250 watts continuous meaning it will run at this level all day if required BUT we ran it at 500 watts with suitable cooling to take advantage of the higher speed attainable - we were racing after all.

how to calculate battery needed by my car to travel 10 km in one charge?

Batteries are rated in ampere hours - typical for a car battery is 70 A/hr so this will provide 70 amps for an hours or 140 amps for 1/2 an hour. Knowing your motor average current draw allows you to get an idea of how long you can run.

In reality a lot depends on stop start, terrain, driving style, weight carried. electronic speed control or not

Our race car could run for 2 hours at 20 - 30 mph on 2 car batteries without dangerously depleting the battery so it was damaged. at this point the batteries were dead.

In 4 hours most cars would cover 120miles+ and a lot further a few a lot less. So your 10 K is fairly easy.

A final word at this point.

A light weight build is essential. The will mean aluminium and may mean carbon or glass fibre.

This will NOT BE CHEAP - Our car fully fitted cost us about £1500 the motor alone was around £200 and many teams fitted a new motor every year. batteries lasted around 2 seasons costing around £70 each.

Your anticipated weight is too high. 250 KG is 1/4 of a metric tonne You need to be in the range of something you can lift up without the batteries in it.

Look at Greenpower the contest ww entered.


There is a lot of knowledge and information there built up over the last 10 years or so.

You may need to look and see if your car will be road legal or what you need to do to make it so. In the UK your limited to 17 MPH or it will become a car and need to be insured, and tested before you can use it on the road.

Research there is much information out there from people who have already gone a long way down this road..

In many circumstances for such a short distance you will be better off with a Velomobile, same build effort but no speed restrictions (it is peddle powered ) and no heavy battery to lug around.