Sylvie Willis
Fuel economy is an important consideration when choosing a car, especially with rising environmental concerns and gas prices. The standard measure of a car's fuel efficiency is miles per gallon (MPG) — the number of miles a car can travel per gallon of fuel. While the type of vehicle, fuel octane, and type of fuel all impact MPG, diesel cars tend to be the most fuel-efficient, followed by hybrid and electric vehicles. Generally, a good MPG is considered to be anything over 40-60mpg, with some vehicles achieving over 100mpg. Driving style also impacts fuel efficiency, with aggressive driving and speeding reducing fuel economy.
Characteristics and Values of Good Fuel Economy for a Car
| Characteristics | Values |
|---|---|
| Miles per gallon (MPG) | 40-60mpg is good fuel consumption for a used car |
| 50mpg+ is an efficient runner for petrol and diesel cars | |
| 36mpg is the average for petrol cars | |
| 43mpg is the average for diesel cars | |
| 59mpg is the average for hybrid cars | |
| 159mpge is the average for full-electric models | |
| Litres per 100 kilometres (L/100km) | Below 6 litres for passenger cars is efficient fuel use |
| 8-12 litres for every 100 kilometres is good for medium-sized SUVs and some lighter trucks | |
| 12-14 litres for every 100 kilometres is average for bigger SUVs and trucks | |
| Type of vehicle | Smaller engines produce better mileage |
| Hybrid and electric vehicles attain the best fuel economy | |
| Mild-hybrid engines and eco-driving modes can reduce fuel consumption | |
| Type of fuel | Diesel cars are usually more economical |
| Quality fuel can lower the friction in your vehicle's engine and improve gas mileage | |
| Driving conditions | Better gas mileage on highways than city streets |
| Driving slower and accelerating slowly improves fuel economy |
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What You'll Learn
Fuel efficiency
Various factors influence fuel efficiency. The type of vehicle, engine size, and driving conditions all play a role. Smaller engines tend to deliver better mileage due to reduced weight and fuel consumption. Additionally, aerodynamic designs can enhance fuel efficiency by reducing drag, allowing vehicles to cover more distance with less fuel.
Aggressive driving behaviours, such as speeding and abrupt braking, can negatively impact fuel economy. Smoothing out your driving style by accelerating gently, maintaining a steady speed, and decelerating gradually can help optimise fuel efficiency. Using cruise control on highways can also contribute to more efficient fuel usage.
When assessing fuel efficiency, it's important to consider the type of fuel and its octane rating. Higher octane fuels burn more slowly, resulting in more efficient engine operation. Additionally, the vehicle's history and maintenance play a role; newer or well-maintained cars often achieve better fuel mileage.
Ultimately, a good fuel economy varies depending on the vehicle type and driving conditions. For petrol cars, an average MPG of around 36 is common, while diesel cars average 43 MPG. Hybrid vehicles offer impressive efficiency, averaging 59 MPG, and fully electric models boast even higher averages of 159 MPGe. In Canada, a good fuel economy for passenger cars is below six litres per 100 kilometres, while larger vehicles like SUVs and trucks average around ten litres per 100 kilometres.
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Aerodynamics
Streamlining the Shape
The shape of a car significantly affects its aerodynamic performance. Sleek and streamlined designs, often seen in sports cars, reduce air resistance, allowing the car to move more efficiently at higher speeds. This results in better fuel mileage. For example, cars with a smooth front end, tapered roofs, and curved edges experience less air resistance than those with boxy shapes.
Minimising Drag Coefficient
The drag coefficient is a measure of a car's aerodynamic efficiency. It indicates how much the shape of a car resists the air moving around it. A lower drag coefficient means the car will cut through the air more efficiently, using less fuel. Car manufacturers aim for designs that minimise the drag coefficient, especially for vehicles intended for highway driving.
Reducing Wind Resistance
Wind resistance increases fuel consumption, especially at higher speeds. Aerodynamic designs help reduce wind resistance by streamlining the car's profile. This includes incorporating features such as a sloping hood, smooth body panels, and flush headlights. These design elements help air flow smoothly over and around the car, reducing the amount of fuel needed to overcome wind resistance.
Impact of Roof Racks and Accessories
Accessories like roof racks, bike racks, and cargo boxes significantly impact a car's aerodynamics. These accessories increase the car's frontal area and disrupt airflow, causing higher wind resistance and reduced fuel efficiency. Removing or minimising the use of these accessories can lead to better fuel economy, especially when driving at highway speeds.
The impact of aerodynamics on fuel economy is more pronounced at higher speeds, such as highway driving. When cruising at steady speeds on a highway, aerodynamics plays a crucial role in reducing drag and wind resistance. This is why cars with aerodynamic designs tend to have better fuel mileage on highways compared to city driving, where slower speeds and frequent stops are common.
In summary, aerodynamics is a key factor in achieving good fuel economy. Car manufacturers are continually refining designs to optimise airflow and reduce drag, resulting in more fuel-efficient vehicles. By considering the shape, drag coefficient, and wind resistance, car designers can enhance a vehicle's aerodynamic performance, leading to improved fuel mileage and lower running costs for drivers.
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Diesel vs. petrol
When it comes to choosing between a diesel or petrol car, there are several factors to consider in terms of fuel economy. Firstly, understanding what good fuel economy looks like is essential. In general, miles per gallon (MPG) is used as a measurement to understand how efficient a car is in terms of fuel usage. A higher MPG indicates that a car can travel a greater distance with a smaller amount of fuel, making it more fuel-efficient and cost-effective.
Typically, an efficient petrol or diesel car will have an MPG of over 50, with petrol cars averaging around 36 MPG and diesel cars averaging 43 MPG. However, these numbers can vary depending on the type of car, with larger vehicles like SUVs requiring more fuel. Hybrid cars offer even better fuel efficiency, averaging 59 MPG, while full-electric models offer the highest efficiency with an average of 159 MPGe.
Now, comparing diesel and petrol cars specifically, diesel cars tend to be more fuel-efficient due to their fuel containing more energy per litre. This means that diesel cars can go further on a full tank and have better MPG ratings. Diesel cars are also more suitable for towing and long journeys as they provide more power at lower engine revs. Additionally, diesel cars produce lower carbon dioxide emissions than equivalent petrol cars, which is an important environmental consideration.
On the other hand, petrol engines have their own advantages. Firstly, unleaded petrol tends to be less expensive per litre than diesel. While diesel cars may offer better fuel economy, the higher purchase cost of these vehicles could be a deciding factor for those on a budget. Furthermore, diesel cars are known to be noisier, and older diesel cars may emit iNOx gases, contributing to poor air quality in urban areas.
It is also worth noting that driving habits and conditions can significantly impact fuel economy. Smooth acceleration, maintaining a steady speed, and gentle deceleration can improve fuel efficiency, regardless of the fuel type. Additionally, features like mild-hybrid engines, start/stop technology, and eco-driving modes can also help reduce fuel consumption.
In summary, while diesel cars generally offer better fuel economy than petrol cars, other factors come into play when choosing between the two. These include initial purchase cost, environmental considerations, driving habits, and the intended use of the vehicle. Therefore, it is essential to consider your specific needs and usage patterns when making a decision.
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Hybrid and electric vehicles
Hybrid vehicles typically have two types of motors: a traditional gas engine with an electric motor, or a plug-in hybrid (PHEV) that adds an electric motor powered by a battery pack. The latter can run independently of the gas engine, achieving even better mileage. Hybrid cars average 59mpg, while full-electric models average 159mpge.
The Toyota Prius, for example, can achieve up to 67.3mpg, and the 2024 BMW 330e is one of the most fuel-efficient sedans on the market, with a combined mpg-e of 76 and an all-electric range of 23 miles. The 2025 Toyota Crown is another example of a full hybrid, capable of running on battery power alone, and it gets nearly 25% better mpg than the Audi A3.
The performance of electric vehicles (EVs) depends on the driving environment, driving patterns, and weather conditions. For instance, studies have shown that EVs are more efficient in warmer temperatures, and their optimal driving speed is between 45 and 56 km/h.
Overall, choosing a hybrid or electric vehicle is a great way to reduce fuel costs and your carbon footprint.
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Driving conditions
Aggressive driving habits such as speeding, heavy braking, and accelerating can also negatively impact fuel economy. Driving more smoothly, accelerating slowly, keeping your speed steady, and slowing down gently will help you use less fuel. Using cruise control on the highway can assist with this. Some new cars also have regenerative braking, which saves the energy generated when slowing down and uses it again, further saving fuel.
The type of vehicle you drive will also impact fuel economy in different driving conditions. Smaller engines tend to be more fuel-efficient than larger ones due to their lighter weight. Additionally, front-wheel-drive vehicles are often more fuel-efficient than all-wheel or four-wheel-drive. Hybrid and electric vehicles generally attain the best fuel economy, although many gas-powered vehicles get over 30 miles per gallon (mpg).
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Frequently asked questions
A good fuel economy for a car is one that allows you to cover a good distance on the least amount of fuel. In the US, this is measured in miles per gallon (MPG). Typically, anything more than 50mpg is an efficient runner for petrol and diesel cars. Diesel cars are usually the most fuel-efficient, with an average of 43mpg, while petrol cars average around 36mpg. Hybrid cars average 59mpg, and full-electric models average 159mpge.
You can check the MPG figure of your car before purchasing, but these figures are the best possible MPG that you can hit in your vehicle and might not reflect real-world driving. The EPA Highway test, for example, involves frequent accelerating and decelerating, and running the air conditioning, which can affect fuel economy.
The type of vehicle, the type of fuel, and fuel octane all impact the fuel economy of a car. Smaller engines generally produce better mileage compared to larger ones because of the vehicle's weight. Diesel cars are usually more economical as diesel is more combustible than petrol, meaning you need less fuel to generate power. Features like mild-hybrid engines, start/stop technology, and eco-driving modes can also reduce fuel consumption.
The way you drive and care for your car can change how much gas you use. Driving smoothly, speeding up slowly, keeping your speed even, and slowing down gently will help you use less gas. Using cruise control on the highway to keep your speed steady can also help save gas.
