how to actually improve your fuel economy

most fuel economy advice is either obvious or nonsense. here is what genuinely moves the number, roughly in order of how much difference it makes.

things that matter a lot

how you drive. hard acceleration and hard braking is the single biggest factor, and it can account for twenty percent or more. looking further ahead and coasting to lights is worth more than everything else on this list combined.

speed. air resistance rises with the square of speed. 120 km/h uses substantially more fuel than 100 km/h for the same trip, and saves you a few minutes.

tire pressure. under-inflated tires cost real fuel, and it is free to fix. check monthly, cold, against the door jamb sticker.

cold, short trips. an engine uses far more fuel until it warms up, so a five kilometre commute is expensive per kilometre no matter what you do. this is also why winter economy is worse: it is mostly warm-up, not the fuel blend.

things that matter some

weight. only if it is real weight. the roof rack you never use costs more than the contents of your boot, because it is aerodynamic drag rather than mass.

air conditioning, a little, mostly at low speed. at highway speed, open windows cost about as much in drag as the compressor costs, so use whichever is comfortable.

maintenance that was already due. a failing O2 sensor, a badly worn spark plug, dragging brakes or an alignment problem all cost fuel. fixing them restores what you had rather than improving on it.

things that do nothing

fuel additives sold as economy improvers. premium fuel in an engine that does not require it. most bolt-on devices marketed on fuel savings.

if any of it worked reliably, the manufacturers would already be fitting it, and they are the ones with the fuel economy regulations to meet.