Most fuel-saving advice is recycled folklore with no numbers attached. Here’s the same advice ranked by what it’s actually worth per year for a typical driver (say 12,000 km a year in a car using around 8 L/100 km, roughly $1,700 of petrol at recent prices).

Fuel-saving habits ranked by yearly dollar value, grouped by tier Tier 1: worth real money Buy at the right time and place up to a few hundred dollars a year Drive smoothly $150–300 a year for aggressive drivers Tier 2: worth a modest amount Remove roof racks & cargo boxes up to $50–100 a year if used constantly Keep tyres at the right pressure around $20–40 a year Clear out the boot a dollar or two a month Tier 3: mostly folklore Morning fills, air-con, idling myths no measurable yearly saving
Bars are calibrated to the guide's printed dollar ranges. Buying at the right time and place, and the Tier 3 folklore habits, aren't quantified in the guide, so those rows carry no bar; rank order and the quoted phrase carry their value instead.

Tier 1: worth real money

Buy at the right time and place: up to a few hundred dollars a year. Nothing you do behind the wheel comes close to this. Sydney’s price cycle swings 25–35 cents a litre, and stations a few minutes apart routinely differ by 20 cents. Timing plus station choice can cut 10–15% off the yearly bill without changing how you drive. The price-cycle guide explains the timing; the finder shows the cheap stations now.

Drive smoothly: up to $150–300 a year for aggressive drivers. Hard acceleration and late braking are the biggest on-road fuel wasters; government fuel-economy guidance puts the penalty for aggressive driving anywhere from 10% to 30%+ in stop-start traffic. If you already drive calmly, there’s nothing left to claim here.

Tier 2: worth a modest amount

Remove roof racks and cargo boxes when not in use: up to $50–100 a year if you drive with them constantly. Aerodynamic drag is real money at highway speeds; an empty roof box can add several percent to consumption. Fitted once a year for a trip, it’s irrelevant.

Keep tyres at the recommended pressure: around $20–40 a year. Underinflated tyres add roughly 1–2% to fuel use, and they wear faster and grip worse, so this one pays even beyond fuel.

Ditch the boot clutter: small. Weight matters, but the 20 kg of stuff in a typical boot costs a dollar or two a month. Clean it out for space, not for savings.

Tier 3: mostly folklore

“Fill in the morning when fuel is denser.” Underground tanks hold a stable temperature; the difference is negligible. Fill whenever the price is right.

“Air-con off, windows down saves fuel.” At city speeds it’s roughly a wash; at highway speeds open windows can cost as much drag as the air-con costs power. Use whichever keeps you comfortable.

“Premium fuel gives better economy.” Only if your car requires it. We’ve done that maths separately.

Idling myths. Modern engines don’t need warm-up idling; driving gently from cold is the warm-up. Long idles (waiting with the engine running) do burn measurable fuel. Switch off if you’re stopped for more than a minute or two.

The takeaway

The two habits that matter are the boring ones: buy fuel at the right time and place, and drive smoothly. Everything else combined is worth less than either one alone.