The Heavy Cost of Clutter
If you treat your car's boot or your ute's tray like a mobile storage centre, you are paying for it at the bowser. For every 45 kilograms of extra weight you carry, your vehicle's fuel economy drops by roughly 1 to 2 per cent. If you spend $200 a month on petrol, lugging around unnecessary tools, golf clubs, or camping gear could be adding up to $48 a year to your fuel bill.
The Physics of Fuel and Freight
The science is straightforward: heavier vehicles require more energy to accelerate and overcome inertia, especially in stop-start freeway traffic. While automotive studies consistently show this 1 to 2 per cent penalty per 45 kilograms, the impact varies depending on what you drive. A small hatchback will feel the strain of a heavy load much more than a large diesel 4x4, but the extra fuel burn happens regardless of your vehicle's size. Changing your driving behaviour and removing roof racks when they aren't in use will also improve your vehicle's aerodynamics, helping you squeeze more kilometres out of every tank.
How Current Fuel Prices Amplify the Cost
With fuel prices fluctuating across the country in July 2026, those small percentage drops in efficiency can quickly add up. Nationally, Unleaded 91 averages 169.7 cpl, with station prices ranging from 155.9 cpl to 185 cpl (a difference of 18.7 per cent).
If you are looking for the most affordable servos, the top 3 cheapest capital cities for Unleaded 91 are currently Geelong (181.06 cpl), Sydney (182.54 cpl), and Melbourne (182.58 cpl). Meanwhile, drivers in Darwin are paying a premium, where Unleaded 91 prices are 6.8 per cent higher at 193.38 cpl compared to Geelong.
For tradies hauling heavy tools in diesel utes, the weight penalty is just as relevant. Diesel sits 5 per cent higher in Darwin (230.98 cpl) than in Geelong (219.94 cpl). Depending on where you live, you might also find savings by switching fuel types. For instance, Brisbane motorists can save 1.2 per cent by choosing E10 (183.61 cpl) over Unleaded 91 (185.85 cpl).
Your Next Step for Better Mileage
Take 10 minutes this weekend to clear out any heavy, unnecessary items from your boot or tray. Once you have lightened the load, ensure your tyres are pumped to the correct pressure for your daily commute. Finally, before you next fill up, check the FuelRadar map on our iOS or Android app. We report fuel prices Australia-wide, helping you find the cheapest fuel nearby to offset any efficiency losses. A lighter car and a smarter fuel stop are the easiest ways to keep your running costs down.
