Guides to fuel consumption and running costs
Evidence-based answers to the most common questions about what a car really uses: real-world consumption, fuel choice, speed, load and ways to save. Every guide lists its sources.
How to work out your car’s real mpg
How to work out your car’s real mpg with the brim-to-brim method, UK and US gallons, and why it won’t match your trip computer or the official figure.
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Real-world vs official fuel economy (WLTP, NEDC and EPA)
Cars use on average 17–20% more fuel than their WLTP rating and 39% more than NEDC. EU and ICCT data, and how to correct for it when costing a trip.
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Air conditioning or windows down? Which uses more fuel
Air conditioning uses a near-constant amount per hour; open windows cost more the faster you go. ORNL and EMPA data for town, country roads and motorways.
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Roof boxes, roof racks and luggage: how much more fuel
A roof box raises fuel use by 10–25% on the motorway, and 100 kg of load by about 2–3%. Data from the US DOE, ADAC and ORNL, and how to reduce the impact.
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How to cut your commuting fuel costs
The drive to work is often the least efficient trip: town traffic, queues and air conditioning. What actually saves fuel, with data and a worked example.
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Campervan and motorhome fuel consumption
How much fuel a campervan or motorhome uses and why: body type, speed, real travelling weight and aerodynamics. With promobil and ADAC measurements.
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Petrol or diesel: which is cheaper for your annual mileage?
A diesel uses 17–26% less fuel but usually costs more to buy. How many kilometres a year it takes to win back the difference, at today’s fuel prices.
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Fuel consumption at 100, 110, 120 and 130 km/h: how much you save by easing off
Dropping from 120 to 100 km/h (75 to 62 mph) saves around 15% fuel and adds 10 minutes per 100 km. Data from ORNL and the ADAC, and what you save per hour.
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Tyre pressure: how much more fuel you use with under-inflated tyres
Tyres 0.4–0.5 bar (6–7 psi) below the recommended pressure raise fuel consumption by 1–5% and wear out sooner. Data from the ADAC and fueleconomy.gov.
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Toll motorway or free road: when is it worth paying?
A toll motorway doesn’t save fuel compared with a single-carriageway road: going faster uses more. What you pay for is time. Here’s what each hour saved costs.
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How to split fuel costs on a road trip with friends (and what each person pays)
Split the fuel there and back between everyone, driver included. What each person pays, what if someone gets out early, and what you can’t charge.
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Winter fuel consumption: why your car uses more in the cold
Cars use more fuel in the cold, especially on short trips: up to 33% lower mpg. Why it happens, what it costs and how to use less.
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Plug-in hybrids: real-world vs official fuel consumption
A plug-in hybrid is rated at 1–2 L/100 km, but private owners use about 4 and company cars 8. Why, and what it costs by how often you charge.
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Regular hybrids: where they really save fuel (town, country roads, motorway)
A hybrid uses about 30% less than the petrol version in town but only 5% less on the motorway. What it saves for your driving, and when it pays off.
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Towing, caravans and bike racks: how much more fuel
A caravan can more than double fuel use; bikes on the roof add 25–34% and on a tow-bar rack only 4–6%. Measured data, and how to use less.
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