Does extra weight and roof racks reduce a car’s mileage?
Roof racks increase aerodynamic drag, cutting mileage by up to 25 per cent at high speeds. Extra weight also forces engines to work harder. Removing unused racks and clearing your boot can significantly reduce daily fuel costs.
Aerodynamic drag
Roof racks and boxes disrupt the smooth flow of air over your vehicle. The Energy Saving Trust notes that this increased wind resistance, known as drag, makes the engine burn significantly more fuel to maintain highway speeds.
The 25 per cent fuel penalty
Carrying a loaded roof box can be incredibly expensive. According to the RAC, a large roof box can reduce your car's fuel efficiency by up to 25 per cent when driving at 70 mph due to the massive air resistance.
Empty racks still waste fuel
Even an empty roof rack is a silent fuel drain. Motoring experts at the AA confirm that an unused rack can reduce your mileage by roughly 10 per cent because it still creates unnecessary turbulence and drag.
The cost of extra weight
Every extra kilogramme requires more energy to move. The US Department of Energy states that for every 50 kilogrammes of unnecessary weight added to your car, your fuel economy can drop by roughly 1 to 2 per cent.
Impact on stop-start traffic
Extra weight is particularly damaging in city driving. Transport analysts explain that constantly accelerating a heavy vehicle from red lights requires more engine power and fuel compared to a lighter car.
Rolling resistance and tyres
A heavier car puts more pressure on the tyres. Automotive engineers warn that this increases rolling resistance against the road surface, forcing the engine to consume more petrol or diesel just to keep the wheels turning.
Easy ways to save
Removing roof racks and clearing out the boot provides instant savings. The Energy Saving Trust recommends taking off external carriers immediately after use to restore your vehicle's aerodynamic profile and improve daily mileage.
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