Fuel Economy: What Genuinely Changes It

Speed

Aerodynamic drag rises with the square of speed, so the fuel required rises steeply above roughly seventy kilometres per hour.

Reducing motorway cruising speed modestly produces one of the largest single improvements available, typically well into double-digit percentages.

It also costs time, which is a real trade-off rather than a free saving.

Tyre pressure

Under-inflated tyres increase rolling resistance and fuel consumption measurably, as well as wearing faster and handling worse.

Check monthly when cold, using the vehicle's specified pressures, which differ between front and rear and between load conditions.

The pressures are on a door pillar or fuel flap label, not on the tyre itself, which shows a maximum rather than a recommendation.

Weight and drag

Roof boxes and bars carry a substantial aerodynamic penalty even when empty. Remove them when not in use.

Unnecessary weight in the boot matters more in urban driving with frequent acceleration than at steady speed.

Open windows at high speed increase drag; air conditioning costs fuel at low speed. The crossover is around town-to-motorway transition.

Driving technique

Anticipating and coasting to a stop rather than accelerating toward a red light.

Smooth acceleration in a moderate rev range, and shifting up earlier in a manual.

Avoiding idling, since modern engines use less fuel restarting than idling beyond a short period.

Journey patterns

Short journeys from cold are disproportionately expensive, since the engine spends most of the trip below efficient operating temperature.

Combining errands into one longer trip is more efficient than several short ones.

This also reduces engine wear and the oil contamination that short trips cause.

What matters less

Fuel additives, which rarely produce measurable improvement in a healthy engine.

Premium fuel in a vehicle not designed for it, which usually offers no benefit.

Filling up at particular times of day, which makes no practical difference.

Measuring it properly

The trip computer is an estimate and is frequently optimistic. Calculating from brim-to-brim fill-ups over several tanks gives the real figure.

Record the distance travelled and the fuel added, and average across at least three tanks to smooth out variation in how the pump cuts off.

Knowing your actual consumption is what allows you to tell whether a change made a difference or simply felt like one.

When economy drops suddenly

A noticeable fall usually indicates a fault rather than a change in driving.

Common causes include a sticking brake caliper, a failing sensor, a blocked air filter, or under-inflated tyres.