The habits that actually improve mileage.
Every fuel-saving list says "drive smoothly". Useless. Here they are ranked by real effect size — with the physics that decides the ranking, and the myths that don't survive it. Then the only test that matters: your own trend line.
Ranked by effect size
- 1. Highway speed. The big one. Aerodynamic drag rises with the square of speed — the jump from 100 to 120 km/h costs far more per kilometer than 80 to 100. Dropping your cruising speed a notch is the single largest saving most drivers can make.
- 2. The right foot. Hard acceleration and last-moment braking burn fuel warming the brakes. Anticipate, lift early, keep it smooth — the classic advice, and it's true.
- 3. Tyre pressure. A few PSI down drags mileage measurably and wears tyres unevenly. Free to fix, needs doing monthly. This is also the first thing to check when mileage drops (see reading your trend).
- 4. Weight and drag. Roof boxes, bike racks and a boot full of "eventually" — every extra kilo costs, and anything on the roof costs double. A full tank vs half tank, by contrast, barely registers (see full tank vs fill-by-value).
- 5. Trip planning. Cold starts are expensive; an engine at temperature is efficient. Five short trips cost more than one combined loop doing the same errands.
- 6. Air conditioning. Real, but the smallest lever on this list — and more nuanced than the myths suggest (below).
The myths, sorted
"Coast in neutral to save fuel." Backwards for modern cars. Fuel injection cuts fuel to nearly zero when you decelerate in gear; in neutral the engine must idle on injected fuel. Keep it in gear, lift early.
"Premium fuel gives better mileage." No. Octane resists knock; it isn't more energy. Run exactly what the manual specifies — premium in a regular-tuned engine buys nothing but the sticker price.
"AC off, windows down, always." Half right. In slow city driving, windows win. At highway speed, open windows spoil the aerodynamics enough that AC is roughly the cheaper choice.
"Fill up in the morning — cold fuel is denser." Fuel is stored underground at fairly stable temperature. The difference is unmeasurable at the pump meter.
The only judge is your own trend
General advice gets you the averages; your car, routes and right foot are not average. Change one habit, drive a month of normal life, and watch the mileage trend — not any single fill, which swings with traffic and partial fills. That's the entire argument for tracking: the chart converts "I think I'm driving better" into a number.
Common questions
Does driving slower really save fuel?
Yes, up to a point — drag rises with the square of speed, so the 100–120 km/h band is the expensive one. Below highway speeds, other factors dominate.
AC or open windows?
Windows in the city, AC on the highway. At speed, disturbed aerodynamics cost about as much as the compressor.
How do I know a fuel-saving habit is working?
Watch the mileage trend over a few weeks of logging, not single fill-ups. FuelCap charts the trend from your normal fill-ups — free on every plan.