here you have the torque

It’s the invisible force that keeps our cars moving. We don’t mention it much, but what is torque? Carbuyer explains…

This is the question that has plagued physicists, engineers and humble motoring journalists alike for generations. We all know what torque is, but trying to explain it without resorting to language that wouldn’t be out of place in a physics PhD thesis is tricky. 

Essentially, torque is a force – like gravity – but instead of causing objects with mass to attract one another, torque is a measure of rotational force. So, in respect to internal combustion engines, torque is how much rotational force the engine produces. 

Different measures of torque 

Torque is generally expressed in two different units. Like power, there are metric and imperial measurements. Newton meters (Nm) is the metric measurement and the default for engineers, physicists and car manufacturers in Europe. 

Us contrary Brits, however, occasionally like to hold on to the old imperial measurements and expressing torque in pounds-feet (lb/ft) is still fairly common here. 

They’re very different units, but you can convert between them like this: To convert a lb/ft figure to Nm, you need to multiply it by 1.35581794833. To do the opposite, multiply your Nm figure by 0.737562149277. Easy! 

What does that torque figure mean? 

You’d imagine that a car with more torque would generally be faster than a car with less – and in general, you’d be right. By now, you may have read our article stipulating precisely what horsepower is.. 

That article states power – measured in brake horsepower – is “the rate at which work is done”. Essentially, an engine with lots of power produces torque very quickly. They’re not one and the same, however. Diesel engines, for instance, often produce more torque than power, while a non-turbocharged petrol engine will often do the opposite. Turbocharging and supercharging are common ways of extracting more power and torque from an engine.

However, like power, maximum torque is not produced across the whole rev range (except with electric motors). Instead, maximum torque – or pulling power – is produced across within a certain band of revs. For maximum performance right across the rev range, you want maximum torque to be produced low down in the range and then have power take over the further up the rev range you go. This provides good acceleration from low to mid revs: the more torque you have low down, the quicker you’ll accelerate. Electric motors produce all their torque at 0rpm, which is why the Tesla Model S accelerates so quickly. 

Cars with more torque will also be better at towing heavy items – so if you’ve got a large caravan or regularly tow a heavy horsebox or trailer, it's a good idea to go for a car with plenty of torque. A big, six-cylinder diesel SUV is generally a good choice.

Hopefully, this guide has gone some way to clearing the murky fog that surrounds the concept of torque.