Don’t bother with the power and torque figures
It’s the first thing most car makers quote when boasting about their latest model and it’s also almost completely pointless – Power and torque explained.
IT IS HUMAN NATURE to want to distil everything down to something easily measurable. Cameras and megapixels. Computers CPUs and Ghz. TVs and diagonal inches. And of course, for cars it is all about power and torque. It’s well known that power sells, particularly for segments such as 4WD wagons, utes and sportscars. Manufacturers even name their vehicles after maximum power outputs, and trumpet their market-leading torque figures.
But it’s all rather missing the point, rather like analysing the chest/waist/hip measurements of a supermodel instead of just admiring what’s in front of your eyes. Just because something’s easy to measure doesn’t make it a valuable means of comparison.
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 wheelnuts on your car with a wheelbrace. 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 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.
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 there, but here aerodynamics plays a huge part as when you double the speed, four times the drag, triple the speed, 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 come into it as for top speed 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 your local 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, as we prove in this article.
How about towing? Well there’s more to towing that just power or torque. The factors affecting tow rating tend not to be engine output but engine cooling, transmission and chassis. Again, 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, but you can’t determine a real-world towing capability from engine output 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 say a Toyota 86 which is noisy, revs high and very low compared to supercharged Range Rover which is supremely refined, tall and is 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.