Drivers paying £150 a year more in petrol and diesel fuel for simple little-known error

Drivers could be spending an extra £150 per year on petrol and diesel due to an often overlooked tyre issue, according to a new study. Under-inflated rubber can increase rolling resistance, which forces an engine to work harder to keep moving.

However, the extent of the issue appears more serious than many would have believed, with a new WhatCar? study showing the horror facing drivers. The new report finds tyres under-inflated by just 1 bar (14.5psi) could cost motorists up to £150 every 12 months in lost petrol and diesel consumption. To investigate the issue, What Car? conducted lab tests of three identical new tyres inflated to different levels.

One compound was inflated to the recommended 36psi (2.5bar), with the second filled to only 22psi (1.5bar) and the third to 51psi (3.5bar). The study found that under-inflating rubber would lead to a 4.5% increase in rolling resistance, compared to usual levels.

Estimates suggest the car would use up around £1.50 worth of additional petrol for every 100 miles driven when fitted to the stock Audi A3 1.5 petrol vehicle used for WhatCar's experiment. Over the course of an annual mileage of 10,000, and drivers should expect to spend an additional £150 on fuel.

WhatCar? consumer editor Claire Evans warned there were also serious safety concerns if motorists were driving around with under-inflated tyres.

She said: "It’s good to know that you’ll save money on fuel if your car’s tyres aren’t over-inflated, but it’s the safety implications of driving with too little air in your tyres that make the most compelling argument for checking tyre pressures regularly.

"Our main tyre test also highlights the significant difference in the handling and braking abilities of different tyres.

"Poorer performing tyres can take up to three metres longer to stop than the best tyres, and that could be the difference between having a near miss or hitting another vehicle in an emergency situation."

Experts have previously warned of the serious consequences of under-inflated rubber on motorists' fuel tank. GT Radial, a motoring expert who carried out extensive testing, claimed fuel consumption rises by 10% when tyres are just 5psi under-inflated.

This would indicate that fuel consumption rises by around 2% for every psi below the recommended level.