# Torque Calculation

I need to know about the torque required for my electric Motorcycle Conversation. Weight is around 200Kg (Including Rider) Tyre diameter is 20 inches Acceleration required around 0-100kmph in 15 sec.. Though I have no idea about inertial force and frictional resistance whatever it is.

• OPPS sorry i type it wrong actually i have removed the Gasoline engine and i want to install an electric motor. My bike would weight about 130 kg and considering 70kg of rider weight total of 200kg i want to accelerate it from 0-100kmph in 15 secs i.e.1.85m/sec2 Also the gear ratio is of 1:4 – Kushal Tayal Dec 1 '17 at 7:42
• Welcome to the site. To help eliminate confusion, please correct the original post using the edit feature rather than posting a comment. – CharlieRB Dec 1 '17 at 15:51

If we Ignore drag, mechanical losses and slip of your tires:

``````Your desired speed is:
100km/h * 1000 m /3600 sec) = 27.7 m/s
You need a total work W of
W = 1/2 m * v² where m is mass and  v is velocity
So you need a total ~384 Nm over a time of 15 seconds
= about 26 Nm per second
``````

Now you need to determine total transformation ratio of gear + drive train + wheel and find a Motor that delivers the appropriate torque to the wheel over the whole rpm-band needed for 0-100. Don´t forget to add drag and losses of your drive train. Also max. power rating of the motor/electronics could limit torque at high rpm.

• So what torque motor i need if in case i m going to use 1:4 ratio from motor to wheel of 20 inches using a chain sprocket the ratio of sprocket is 1:4 – Kushal Tayal Dec 1 '17 at 10:12
• @KushalTayal this site is NOT a design service : you need to start showing what you have worked out so far ie how have you incorporated the result just given to you by Daniel... – Solar Mike Dec 1 '17 at 10:56
• What was the power output and torque of the original motor you removed : this would, at least, put you in the correct ball-park... – Solar Mike Dec 1 '17 at 10:58
• This is more of a theoretical calculation anyways, there are a lot of if´s. If you want a real-world application, look at performance of similar vehicles. – Daniel Dec 1 '17 at 11:02

Let's use a different approach, let's calculate the kinetic energy of the vehicle at 100km/h:

Ke = 1/2 * m * V^2

0.5 * 200 kg * ((28 (m / s))^2) = 78 400 joules

so if we want to do work for 80000J in 15s we need a power of:

80000/15 5300W, or around 5KW.

Considering losses and air drag a 10KW electric engine should do the trick with the proper transmission system. This is a rough estimate but I think it is not far from being correct.