What’s the difference between torque and power?

Is there a difference between power and torque?

ASK ANY CAR ENTHUSIAST about power and torque and 90% of the time they’ll say they know the difference, but actually…they don’t. Yet us 4×4 people take it as read that torque is good, and power is, well, umm, don’t we really need torque? Isn’t power for racecars?

So let’s define what torque and power are from a real-world perspective.

Torque is simply rotational turning force. When you work on the wheel nuts on your 4X4 you are using torque to undo, or do up those nuts. And power is how quickly that force (torque) is applied.

That’s it! Super simple.

To fill out those definitions a bit more – if you were put your 4X4s on a flat concrete pan you could push it 100m or so. Might take a while, but the average human adult is strong enough. In physics terms, we say you have done work, you’ve moved 2500kg of vehicle 100m.

The engine in your 4X4 can do the same job of moving that 2500kg car a distance of 100m. The difference is that the engine can do it a lot faster than you can, which is why we consider the engine more powerful than the adult human. Power is all about time remember, which is why dynos only measure torque and then derive power through revs, which is a time-based calculation.

Here’s another example. If you have a breaker bar of around 2m in length you can probably generate 400Nm of torque, which is the same as many 4X4 engines. Sounds impressive, doesn’t it…you can equal or even out-torque a diesel engine!

But of course there’s a difference. Your breaker bar is connected to a nut. How many times in a minute could you spin 360 degrees that 2m-long breaker bar? Once, if you’re lucky. Now what about the engine? Let’s try 2000rpm, or revs per minute, or 33.3 times per second. See the difference? Same amount of torque, different amount of power. And because the engine spins that fast it can be geared down to produce much, much more torque, trading rotational speed for turning force.

You already understand that tradeoff, as you would have shifted down to climb a hill. That’s when you demand greater turning force from the engine, sacrificing top speed which is dependent on how fast the torque is delivered, or power.

So, how do you feel about only focusing on torque figures now? But what’s better, lots of kilowatts or lots of newton-metres?

Next time we’ll get into what really matters when driving and setting up a 4×4 – torque or power.

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Robert Pepper

Robert Pepper