How are Nm calculated for vehicles?

Question

To my understanding 1Nm is a force of a 100g pushing down on the 1m long rod. But new Ducati Panigale produces torque of 140Nm. Does it mean that 14kg pushing on 1m rod can stop the engine? It seems way to low.

In: 1

Answer 1

Calculations of torque are based on normal earth conditions. However the translation of torque to pavement isn’t solely based on the motor itself. Tractive effort is what drives the car. The power train multiplies the torque from the motor to the wheels through gearing. The motor itself isn’t receiving the stress of the weight of the car.

Answer 2

It’s one newton, which is *about* the weight of 100g on Earth.

But yes, that’s exactly what it means. A meter is a pretty long lever. The diameter of the vehicle’s wheels will be closer to half a meter, so a radius of 1/4 a meter. That means that 14 kilograms of ‘force’ on your meter lever is the same as 56 kilos on the wheels.

But that’s not all. The engine is not directly connected to the wheels. It has gearing, and these gears exchange movement speed for torque. This means that, with the right choice of gears, your wheels can have as much torque as you want, provided your engine spins fast enough to compensate. The quoted torque I could find for that vehicle was at 7,000-some RPM which is quite fast. A half-meter wheel at 70 km/hr will be spinning at around 800 rpm, which is way slower, so the engine can have a large gearing ratio applied to it even at that speed, multiplying its torque at the wheels quite a bit.

Answer 3

Well, one thing to keep in mind here is that if Torque is Weight * Distance…you’ll get A LOT of weight if you shorten the distance. Imagine instead that you have those 140Nm about 1cm from the centre of the rotating axis?

14kg * 1m = 140Nm = 0.01m * 1400kg.

Should, if you boil it down, be able to set a 165kg motorcycle in motion, don’t you think?

There is a lot more to the equation than that, but…uh…my perfectly typical hatchback has a torque number at 350Nm or something like that. 140 on a motorcycle sounds like more than enough, even with that simple comparison.