Don’t worry about power and torque
Power and torque is the first thing most car makers quote when boasting about their latest model and it’s also almost completely pointless.
IT’S MUCH SIMPLER to distil something down to comparable metrics than figure out real-world performance. We do it with cars – a lot – but also things like computers, TVs and smartphones. We compare things like power and torque, inches and nits, and ram and gigahertz.
In car land, it’s well known that power and torque sell, particularly for segments such as 4WD wagons, utes, and sportscars. Manufacturers even name their vehicles after maximum power outputs and tout their market-leading torque figures.
But that’s not always an indication of what’s better.
What’s power and torque?
First, let’s clear up a couple of quick definitions. Torque is turning force. Power is how quickly that turning force is applied.
You can, for example, undo the wheel nuts on your car with a wheel brace. So too can a rattle gun. You both produce the same torque to do or undo the nuts, but the rattle gun can do it a whole lot quicker, so it is more powerful. A lot of torque at a slow rotational speed gives you a certain amount of power, the same as less torque at a higher rotational speed.
Why those figures ‘don’t matter’
But we’re getting complicated, which isn’t the point of this article. The point is that power and torque measurements are simplistic, and are given far too much attention when people compare cars. We just touched on some of the complexities above, but there’s more to it than a physics lesson.
For example, most people are interested in power because of acceleration. So then you need to know the weight of the vehicle which has a huge effect on how quickly you gather speed. Gearing is a big factor too, as is the power and torque curve of the engine, distinct from its peak output which is the headline quoted figure.
So if you’re interested in acceleration, look at the 0-100 figures, not the power. You may as well try and work out the nutritional value of a sandwich from analysing the newly-harvested wheat used for its bread.
Or maybe you’re interested in power because of top speed. Sure, power is a factor, but aerodynamics plays a huge part as when you double the speed you get four times the drag; triple the speed, get nine times the drag.
Sound wrong? Why then, all else being equal, doesn’t a 300Kw car have anything like twice the top speed of a 150Kw car?
Interestingly, weight doesn’t really count much for top speed because you can get there as slowly as you like, just as long as you get there. But in the real world, you don’t have the Bonneville Flats at your disposal so your heavy car with a high top speed may be slower down the straights at a track than a better accelerating car with a lower top speed.
OK, so power is by no means the whole answer for acceleration or top speed. In fact, acceleration is all about torque.
Do torque and power affect the tow rating?
Well there’s more to towing than just power or torque. The factors affecting tow rating tend not to be engine output but engine cooling, transmission, and chassis. Look at the likes of the 90kW Defender, rated to 3500kg, and the Prado, around 140kW, rated for 2500kg. The Nissan Patrol GU was rated from 3500kg to 2500kg depending on engine and transmission. Don’t get me wrong, power is lovely and the Prado will be much nicer to tow than the Defender in this example, but you also can’t determine a real-world towing capability from engine spec alone.
So to be honest, I can’t think of a single reason why you’d look at power figures, as for any meaningful real-world performance consideration you’re better off looking at the end result figure such as towing capacity, acceleration or top speed.
But even those performance figures can lead you astray.
The sensation of acceleration is very different in a Toyota 86 which is noisy, revs high and sits very low compared to a supercharged Range Rover, which is supremely refined, tall and relatively much lower revving.
The Toyota is slower, but feels faster – more on that in this comparison.
And some engines belie their meagre output because of a beautiful power delivery curve, yet others are so peaky you never feel like the car is living up to its claimed power.
If there’s one thing I’ve learned as an auto journo it’s that you can’t rate a car by its specifications any more than you can rate a book by measuring its cover.
Do you have something to add? Get involved in the conversation below or join our Facebook community.