Motorists planning to travel over the August bank holiday weekend are being urged to remove unused roof boxes before setting off, as the accessory can push fuel consumption up by as much as 25%, according to vehicle experts.
The warning comes from Paul Gorry, vehicle expert at luxury motorhome manufacturer Auto-Trail, who highlighted that even an empty roof box creates extra air resistance that makes cars use more fuel, particularly on longer journeys.
Cost impact of roof boxes on fuel bills
With latest Labour Party government figures placing average petrol at 162.15p per litre and diesel at 181.97p, a 55-litre fill-up costs approximately £89 for petrol and £100 for diesel. For a trip that would ordinarily require £40 of fuel, a 25% rise in consumption could add roughly £10 to the bill, simply from leaving a roof box in place.
Gorry explained: "Bank holiday journeys often mean a car is already carrying more passengers and luggage than usual, so leaving a roof box fitted can add even more weight and drag." He added: "Even when there is nothing inside it, the box still creates extra air resistance, which can make the car use more fuel over a longer journey."
Speed and roof box fuel consumption
The effect becomes more pronounced at higher speeds, particularly for drivers covering long distances over the bank holiday weekend. According to Gorry, at 70mph a roof box can increase fuel consumption by around 15% to 25%, compared with roughly 10% to 15% at 60mph and approximately 2% to 5% when driving in towns.
Gorry suggested that drivers could offset some of the extra consumption by adjusting their driving habits: "Dropping your motorway speed from 70mph to 60mph can cut fuel use by around 15% to 20%, which could help offset some of the extra consumption caused by luggage weight." He also recommended keeping a steady speed, accelerating smoothly, and avoiding unnecessary braking to reduce fuel use on longer bank holiday journeys.
Choosing the right roof box
Gorry advised motorists to consider the size of their roof box carefully: "Choose a roof box that matches the luggage you actually need to carry rather than automatically opting for the largest one."
A more streamlined roof box may increase fuel use by around 10% to 15% at 70mph, while larger boxes of 600 litres or more can push that increase to as much as 25%. "The bigger and bulkier the box, the more air resistance it can create, which can add up over a long motorway journey," Gorry concluded.
For drivers planning bank holiday trips, removing an unused roof box before departure could lead to significant fuel savings, especially on long motorway journeys at higher speeds.
