How to cut your fuel bill
Most fuel-saving advice is a long list of small things. Two or three of them account for nearly all of the saving, and they are not the ones usually listed first.
1. Choose the forecourt, not the moment
The single largest saving available to most drivers is simply not filling up at an expensive site out of habit. The spread within one town is routinely 10p a litre or more, which on a 55-litre tank is over £5 a fill — repeated every fortnight, that is well over £100 a year for no change in behaviour beyond looking first.
This dwarfs every driving technique on this page, and it takes about ten seconds.
2. Slow down on the motorway
Aerodynamic drag rises with the square of speed, so the fuel needed to overcome it rises sharply. Driving at 80 mph rather than 60 typically uses around a quarter more fuel over the same distance.
On a 200-mile journey in a 45 mpg car, that is roughly 5 extra litres — about £8 at current prices, to arrive perhaps twenty minutes sooner.
3. Take the roof box off
An empty roof box or roof bars left on all year is one of the most expensive habits in motoring. At motorway speeds a roof box can add 10-20% to fuel consumption, and cyclists' racks are not much better.
It costs nothing to remove and takes minutes. If it lives on the car between trips, it is quietly costing more than most of the other measures here save.
4. Check your tyres
Under-inflated tyres increase rolling resistance. Running 10 psi low typically costs around 2-3% in economy, and it wears the tyres faster and lengthens braking distances, so the case does not rest on fuel alone.
Check them cold, monthly, against the figure on the door pillar rather than the number moulded into the tyre — that is the tyre's maximum, not your car's recommendation.
5. Lose the weight you are not using
Extra mass costs fuel mainly in acceleration, so it matters more in town than on a motorway. The effect is real but modest: roughly 1-2% per 50 kg.
Worth clearing out genuinely heavy items you are carrying pointlessly. Not worth agonising over.
What does not work
Fuel-saving devices sold as magnets, vortex generators or fuel-line gadgets have no credible independent evidence behind them. Neither does filling up at a particular time of day.
Air conditioning is a smaller factor than folklore suggests: at motorway speeds, running the air conditioning generally costs less than driving with the windows open, because open windows spoil the airflow over the car.
Common questions
What saves the most fuel?
Choosing a cheaper forecourt. The price spread within a single town is often 10p a litre or more, which is a larger saving than any driving technique and requires no change in how you drive.
Does driving slower really save fuel?
Yes, substantially at speed. Drag rises with the square of velocity, so 80 mph typically uses around 25% more fuel than 60 mph over the same distance.
Do fuel-saving devices work?
There is no credible independent evidence for magnets, vortex generators or similar fuel-line gadgets. The measures that work are unglamorous: where you buy, how fast you drive, and what you are carrying.