What All Those Motoring Numbers Really Mean

Car mechanics, like lawyers, have a poor reputation when it comes to being entirely honest with their clients. If you find a dependable one, hang on to him like grim death, even if he’s located in the next city over. I remember one time when I had to ask one of these individuals to point out the drive shaft on a front engine, front wheel drive car he supposedly replaced…my bill got recalculated pretty quickly after that.

The Value of Educating Yourself

Likewise, car salesmen have been known to be economical with the truth when it comes to things like selling financing and additional options. The thing to realize is that your and their interests do not normally coincide and they will usually have an advantage over you when it comes to industry knowledge. However, they typically know less than they pretend to, and by arming yourself with an understanding of what they talk about, you can ensure that your “fuel-efficient” car really is just that.

When you’re a demanding customer (and most people are when it comes to their transport), you will want to know what you’re getting for your money. If you were selecting an air compressor that matches your needs, you’d quickly realize that only a handful of specifications actually matter when comparing different models. The good news is that this is also true of cars.

Miles per Gallon/Kilometres per Litre

Car's Engine

This might seem to be the single most important figure that someone looking for a fuel-efficient car should consider. Unfortunately, it is also the one fudged most often by manufacturers.

The best number you will see will always be the one taken while driving on a level road, without accelerating or slowing down and at the engine’s most efficient RPM (the speed the crankshaft turns at). This in no way resembles the actual experience you will have in the city when going 30 km/h from traffic light to traffic light.

When a car’s speed is constant, the only work the engine has to do is to overcome the friction associated with the transmission, tires and air flow. When accelerating, though, Newton’s Second Law comes into play and you’ll have to step on the accelerator a little bit harder. This energy expenditure is (normally) not recouped when braking, so you’ll end up using significantly more fuel to cover the same distance.

Luckily, there are a number of independent third parties who test vehicles under more realistic circumstances. Put down the pamphlet the salesman gave you and trust them instead when it comes to MPG or KPL figures.

Torque and Power

These measurements refer to the performance of your car, and just because you care about the environment doesn’t mean that you have to buy the most anemic little chariot you can find.

The simplest way to explain the difference between the two is that power, given in kW or horsepower, is the “vroom vroom” of the engine, while torque in N.m is the “push push”. A higher power rating means that you will be able to accelerate faster, while (for manual transmissions) a high-torque engine requires fewer gear changes.

You will also see the number of cylinders and their total displacement mentioned in this regard (for conventional petrol and diesel engines, anyway). Most people needn’t worry about the number of cylinders. The displacement in cubic centimetres or litres pretty much reflects the engine’s power output, at the cost of higher fuel consumption.

Sports Car

Counting Costs

People who opt for fuel-efficient cars generally do so for two reasons: to save money on fuel and to reduce their carbon footprint. However, few of them have actually taken the time to examine these effects beyond thinking of an eco-car as “a good thing in general”.

The average driver will save no more than a few hundred bucks a year by choosing an efficient car, which may cost thousands more than other models. If you haven’t done the math already, it’s high time that you do. In much the same vein, someone who wants to fight global warming can do far better by not eating meat for one day a week – cattle farming has a greater effect on climate change than all forms of transport combined.

Whatever your motivation, you should take into consideration that buying a “green” car is often more of a fashion statement than a conscientious decision. Slight changes in your lifestyle may be far more effective at saving both money and the environment; taking the train to work, for instance.