What is torque?

The majority of us know what torque is but would struggle to explain it succinctly without getting tangled up in mechanical physics. Giving a simple explanation that’s easy to understand has troubled many physicists, engineers and humble motoring journalists alike for several decades. However, in this in-depth guide we’ll break down the concept of torque to help you understand exactly what is.

Torque is often described as a twisting force, others prefer the more detailed description of a ‘rotational equivalent of linear force’. Either way the critical element to understand is that the torque of an engine is the maximum force it can deliver.

You can think of torque as effort, as it would be when tightening a wheel bolt on your car. Whatever the torque number that is required for the bolt to be correctly tightened will require a specific amount of effort. An engine or an electric motor is similar to you, it has a maximum amount of effort it can reach. When you press the throttle pedal in a car you are demanding effort of it, up to the maximum amount it can deliver. When this is used to turn one or more wheels, that is how we can measure the final output torque.

A slower car and faster car will be separated by the amount of torque they have, and how quickly it can be delivered. The speed of which it can be delivered is our horsepower measurement. Having a very fast rate of torque delivery may suit one vehicle, but not another, depending on its use.

Different measures of torque

Your location in the world will likely differentiate the value used to measure torque. Newton metres (Nm) is commonly used in Europe by car manufacturers and by engineers and physicists using the metric system. Pounds-feet (lb/ft) is common in the USA and traditionally also in the UK, as it’s an imperial measurement.

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. Although torque is generally preferred by those requiring immediate low down power, as is common in a diesel engine, or an electric motor. For that reason they can also be fairly slow as their purpose is delivering maximum torque at low wheel speed to move heavy objects. This all depends on the gear ratios used to transfer power from the electric motor to the wheels. By now, you may have read our article stipulating precisely what horsepower is. If you haven’t, you can find it here.

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.

Why is torque important in a car?

Similar to a car’s maximum power or brake horsepower (BHP) measurement, maximum torque is not produced across the whole rev range (except in electric motors, which work differently). Instead, maximum torque – or pulling power – is produced in a certain part of the rev range. Some vehicles engines are intended for use in particular situations and are set up accordingly but generally speaking, the ideal scenario in a car is to have balanced performance right across the rev range. This usually means the maximum torque figure is at relatively low revs, where it’s useful at helping the car accelerate; torque is less useful once the car is travelling at higher speeds. It also gives the car more pulling power from low to mid revs. Electric motors are capable of delivering all their torque instantly, which is why cars like the Tesla Model S and Porsche Taycan are capable of lightning-quick acceleration.

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Cars with more torque are also 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. Hybrids along with diesel engines and even electric cars are generally a good choice, although you should remember towing will decrease the driving range of all vehicle types. 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. To find out more about horsepower, read our article here.