Regan Brown
The fuel economy of a car, or the number of miles it can cover per gallon of fuel, is an important factor for many car buyers. However, official fuel economy figures are often not reflective of real-world driving conditions and can be misleading. This is where Real MPG comes in: it provides genuine data from real drivers, allowing car owners and buyers to understand how much fuel a vehicle consumes on the road. While the Worldwide Harmonised Light Vehicles Test Procedure (WLTP) replaced the NEDC test in 2017 to better reflect real-world driving conditions, it is still a laboratory-based test and cannot account for variables such as weather, car occupancy, and traffic congestion, all of which impact fuel economy.
Real Fuel Consumption Characteristics
| Characteristics | Values |
|---|---|
| MPG Definition | Miles per gallon (MPG) is a way of measuring a car's fuel economy or consumption. It tells you how many miles your car will cover on a gallon of fuel. |
| MPG Calculation | Can be calculated manually by filling the car with fuel, recording the mileage, driving until low on fuel, filling the car again, and recording the litres of fuel added. This can then be converted to gallons and the MPG calculated. |
| MPG Variation | MPG varies based on driving conditions, including weather, car occupancy, and traffic congestion. |
| Real MPG | Refers to genuine real-world data from real drivers, reflecting the actual on-the-road fuel consumption of a vehicle. |
| Official MPG vs Real MPG | Official MPG figures from manufacturers are often higher than what drivers experience in reality. Real MPG figures provide a more accurate representation of fuel consumption across different roads and driving conditions. |
| WLTP | Worldwide Harmonised Light Vehicles Test Procedure is used to determine the official MPG figures for new cars. It includes tests at different speeds to replicate city, suburban, main road, and motorway driving. |
| Vehicle Examples | Skoda Kodiaq vRS, Citroën C3, Ford Ranger, Dacia Duster, Lexus ES 300h, Honda Accord Hybrid, Kia Niro, Hyundai Elantra Hybrid, Volvo S60 Plug-In Hybrid |
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What You'll Learn
Calculating your car's MPG
Firstly, it's important to note that your driving style has a significant impact on your MPG. Driving aggressively, with fast acceleration, frequent braking, and high speeds, will negatively affect your MPG. Additionally, driving in cold weather and towing extra weight, such as a trailer or roof rack, will also reduce your MPG.
To calculate your car's MPG, you can use a simple formula: MPG = distance (miles) / average gas consumption (gallons). This formula is based on the relationship between the distance travelled and the amount of fuel burned. You can also use an online MPG calculator, which will estimate your fuel efficiency based on the distance covered and your car's average fuel consumption.
Modern cars have an engine management system that can automatically calculate and display the average MPG by dividing the distance travelled in miles by the amount of fuel consumed in gallons. Your car's computer precisely monitors the flow of fuel into the engine and uses sensors, such as an odometer, to measure the distance travelled. This closed-loop system allows the computer to make constant adjustments to ensure optimal performance.
To improve your fuel efficiency, consider the following:
- Keep your vehicle well-maintained: Use the recommended motor oil, ensure the oxygen sensor and air filters are in good condition, and keep the engine properly tuned.
- Reduce unnecessary weight: Remove heavy items from your car, and avoid towing trailers or using roof racks if possible.
- Optimise tyre performance: Ensure your tyres are properly inflated, as under-inflated tyres can lower gas mileage. Check your tyre pressure regularly, as it can be affected by temperature changes.
- Plan your routes: Use highways instead of local routes or city streets, and park in a central location when driving in a city to reduce stop-and-go driving, which negatively impacts fuel efficiency.
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Real-world fuel economy
For years, the official fuel economy figures stated by car manufacturers were often far higher than what drivers experienced in reality. This left drivers frustrated and burdened with higher fuel costs than they had anticipated. Miles per gallon (MPG) is a measure of a car's fuel economy or fuel consumption, telling you how many miles your car can cover per gallon of fuel.
The Worldwide Harmonised Light Vehicles Test Procedure (WLTP) is how all new cars are tested to determine their official MPG figures. The test is designed to be more reflective of real-world driving conditions than its predecessor, the NEDC test, and it has indeed resulted in a smaller gap between the figures. However, it is still a laboratory-based test and cannot account for factors such as weather, car occupancy, and traffic congestion, all of which significantly impact fuel economy.
To address this issue, some organisations have developed their own Real MPG tools. These tools provide real-world data from actual drivers, giving prospective buyers a more accurate understanding of how much fuel a vehicle uses on the road. For example, What Car? has identified several car models that beat their official fuel economy figures, including the Skoda Kodiaq vRS, which delivered a near 43% improvement.
Additionally, there are now apps available, such as Spritmonitor.de, that can help you calculate and track your car's fuel economy and manage vehicle costs. These apps allow you to record fuelings directly at the gas station and provide additional features with a free account registration.
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How rims affect fuel consumption
The rims on a car can influence fuel consumption, with larger rims generally leading to increased fuel usage. The weight and diameter of rims and tyres can directly impact a vehicle's momentum. Wider rims with larger diameters will increase momentum, requiring more torque and fuel from the engine.
The relationship between rim size and fuel consumption is not linear. Moving up or down an inch in rim size will only result in a minor change in fuel efficiency, typically around 0.1 km/L. However, as the difference in rim size becomes more significant, the effect on fuel consumption becomes more apparent. For example, the difference in fuel efficiency between 16-inch and 17-inch rims is negligible compared to the impact of switching to much larger rims.
The weight of larger rims contributes to increased fuel consumption. Heavier rims demand more energy to overcome their mass and get the car moving, leading to higher fuel usage over time. Additionally, larger rims often require wider tyres, which increase rolling resistance, further reducing fuel efficiency.
However, it is important to note that other factors can influence the impact of rim size on fuel consumption. For instance, if you frequently drive at high speeds on freeways, larger rims can enhance fuel efficiency. This is because larger rims can reduce overall resistance at higher speeds, requiring less fuel to maintain momentum.
Furthermore, lightweight rims made from alloys or other lightweight materials can mitigate the negative impact on fuel consumption. These rims weigh less than standard rims, reducing the overall weight of the vehicle and minimising resistance. However, opting for lightweight rims may limit the types of tyres that can be used, and wider tyres may still be necessary, partially offsetting the fuel efficiency gains.
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Cars with the best gas mileage
When shopping for a new car, one of the most important factors to consider is the vehicle's efficiency. While most modern vehicles are far more efficient than older models, some cars outperform others. Here are some of the best cars with the best gas mileage:
2024 Toyota Prius Prime
The Toyota Prius Prime is a highly fuel-efficient car, delivering a combined average of 127 mpg for electric and gas driving and 52 mpg in Hybrid mode in the entry-level SE trim. Its all-electric driving range is 45 miles. The 2024 model has improved fuel economy and driving dynamics, offering up to 196 horsepower.
2024 Hyundai Elantra
The Hyundai Elantra is a stylish and pragmatic choice, offering good fuel economy and an array of standard tech features. Among the non-hybrid Elantras, the base SE model with a 147-hp, 2.0-litre four-cylinder engine, and a continuously variable automatic transmission (CVT) is the most fuel-efficient, achieving 32/41/36 mpg.
2024 Mitsubishi Mirage
The Mitsubishi Mirage is the most fuel-efficient gas-powered car currently available and is also the most affordable, with a starting price below $18,000. The Mirage hatchback is rated at 36/43/39 mpg (city/highway/combined), while the Mirage G4 sedan achieves 35/41/37 mpg.
2024 Honda Civic
The Honda Civic offers both sedan and hatchback body styles, with the mid-level EX model being the most fuel-efficient. It is rated at 33/42/36 mpg and is powered by a 1.5-litre four-cylinder engine with a CVT.
Lexus ES
The Lexus ES is a reasonably priced mid-size luxury sedan that offers a smooth driving experience, a plush interior, and numerous safety features.
It is worth noting that factors such as driving conditions, weather, car occupancy, and traffic congestion can affect a vehicle's fuel economy. Additionally, the Worldwide Harmonised Light Vehicles Test Procedure (WLTP) provides a range of MPG figures (Low, Medium, High, and Extra High) to reflect different driving conditions.
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Fuel economy ratings
While MPG is a useful metric, fuel costs are calculated per litre in the UK, making it necessary to convert gallons into litres for cost calculations. A gallon is approximately 4.5 litres (4.546 litres to be precise), so if fuel costs £1.50 per litre, it costs £6.80 per gallon.
Previously, manufacturers would list three different MPG figures: Urban, Extra-Urban, and Combined (the average of Urban and Extra-Urban). However, thanks to the WLTP (Worldwide Harmonised Light Vehicles Test Procedure) test, a broader range of MPG figures are now provided under Low, Medium, High, and Extra High. These categories represent driving conditions in different areas, with vehicles tested at 35mph, 47mph, 60mph, and 81mph to simulate city, suburban, main road, and motorway driving, respectively.
Despite improvements, the WLTP test is still conducted in a laboratory setting and cannot account for real-world variables such as weather, the number of passengers, and traffic congestion, all of which impact fuel economy. To address this, HonestJohn.co.uk introduced the Real MPG feature, which provides real-world data from actual drivers, helping owners and buyers understand the vehicle's on-road fuel consumption more accurately.
Additionally, several online tools and calculators are available to help drivers calculate and manage their car's fuel economy and associated costs, such as Spritmonitor.de and FuelEconomy.gov, the official US government source for fuel economy information.
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Frequently asked questions
You can calculate your car's real fuel consumption by filling your tank to the brim, recording the mileage, then filling up again and recording how much fuel you've used. Convert the litres into gallons, subtract the starting mileage from the current mileage, and then divide the miles covered by the gallons of fuel used.
You can improve your car's fuel economy by changing up to a higher gear earlier and avoiding hard acceleration. You can also reduce weight by clearing out the boot and closing your windows.
MPG stands for miles per gallon. It's the number of miles a car can cover on a gallon of petrol or diesel.
The most efficient cars on sale today average around 60mpg, but anything over 50mpg is impressive.
On average, manufacturer fuel consumption figures are 15-20% lower than actual consumption. This is because real-world fuel consumption is affected by factors such as traffic, weather conditions, and driving style.
