Small Cars Might Not Be As Fuel Efficient As You Think They Are

• Usman Ansari


• 24 Nov 2015

When it comes to owning a car, fuel efficiency is a primary point of concern for most automobile users in developing countries like Pakistan. With the ever expanding cities of today, the distances we have to travel using our vehicles are on a rise. Most of us prefer to have a car which gives the best mileage, be it petrol or CNG, hence small cars with smaller engines are the ones found in majority here. But the question is, are the engines with smaller displacement actually fuel efficient?

There are certain perceptions developed in our market about vehicle segments and engine displacements, which needs to be corrected considering the technology that is available to us today. Here, regardless of the technology, majority of people still consider 1000cc or below engines to be fuel efficient, while 1300cc or bigger engines to be fuel guzzlers. However, this particular concept is not entirely correct. The fuel efficiency of a vehicle largely depends on the power-to-weight ratio, in addition to the displacement of the engine as believed.

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The displacement of an engine is the volume of total air displaced by the pistons in all of an engine’s cylinders and is calculated in cubic centimeters, or liters. The output of an engine is measured in torque or horsepower. Torque measures the pulling power of an engine, while horsepower indicates how much sustained work the car can do. To put it in a simplest way, think of the engine displacement as a drink bottle, the bigger the bottle the more fluid you can put in it, and the more you are able to drink. Think of output as the amount of calories (energy) in that bottle. This should be able to help understand the basic concept of relationship between engine displacement with the output (Torque/ Horsepower).

While smaller engines may be fuel efficient in one way but in most circumstances they require more power to move around compared to the cars with bigger engines. A 660cc engine may need a lot of power from the engine, when it is loaded with say 5 passengers, air-conditioning, climbing uphill, accelerating at higher speeds, etc as compared to a larger engine. A 1300cc engine working under the similar circumstances will require much lesser effort to do its job. This results in more wear & tear and shorter engine life of a smaller engine as compared to the bigger engine.

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A study was carried out in UK last year. While drivers are often led to believe that smaller cars can travel more miles per gallon (mpg), research by Emission Analytics found that they often use up more fuel because they generally have to work harder to accelerate. Tests on 500 vehicles, half petrol, half diesel, each driven for three hours on roads in Britain, found that the cars traveled on average 18 percent fewer miles per gallon than stated in manufacturers’ specifications.

It should also be kept in mind that modern day engines, with sophisticated technology are much more efficient in fuel consumption as compared to the smaller engines from couple of decades ago. Manufacturers deploy a certain engine into a vehicle considering the power-to-weight ratio. Most of the people in our market still believe that the 1300cc engine offered in hatchbacks these days aren’t fuel efficient, instead they should be offered with 1000cc engines as we are used to it. This concept is incorrect. The 1.3-liter found in a Suzuki Swift is offered because it can carry its weight and perform day to day tasks much easily & efficiently as compared to a 1.0 liter engine. However this does not lead to a conclusion that engines with higher displacement are always fuel efficient. Swift with a 1.6-liter engine will always require more fuel since the power it would develop will be more than the standard needs of a hatchback of this size. Similarly the Toyota Belta offered with a 1000cc engine is known to be sluggish in our market, as compared to the 1300cc version which has a slightly better power-to-weight ratio.

The question now comes, why not the car makers give us the engine with the best power-to-weight ratio only. Toyota Corolla in our market is offered with 3 different engines, 1.3-liter, 1.6-liter and 1.8-liter. It’s because manufacturers offer different trims, configurations & engine options in a single car to cater to a wide variety of customers, some of whom prefer performance, others prefer economy. Since taxation of automobiles is based on engine displacement, vehicles with smaller engine displacement get the benefit and are largely preferred especially in developing countries.

We can calculate power-to-weight ratio by taking vehicle’s horsepower and divide it by its curb weight. The higher the number, the better your car is going to be in terms of performance. In addition to power-to-weight ratio, other factors like how you drive, vehicle maintenance, traffic conditions, quality of fuel and tire pressure etc also play an important role in determining fuel efficiency of a vehicle. It is because of this very reason that fuel consumption cannot be proportional to engine size in real world.

Though we have little options in our market, it’s always good to look for a product that fits your need rather than going after the herd and buy whatever everyone else is buying. People blindly believe that every 1000cc hatchback consumes less fuel than the 1300 hatchback, and every 1300cc sedan is fuel efficient than a 1500cc one. Here manufacturers don’t provide basic information like curb weight, power-to-weight ratio etc, at least not available on their websites and spec sheet. Rather than just looking for an engine with smaller displacement, consider its weight, horsepower/torque as well. While making a car buying decision, do keep in mind that bigger engines can yield better results than a smaller engine working under stress.