Should you drive below the maximum authorized speed to save money, or save time by driving as fast as possible?

We often point to the virtues of eco-driving, this practice which aims to limit the fuel consumption of your car as much as possible. Eco-driving requires constant attention and requires you to look as far as possible at all times, in particular to optimize the slowing down phases when approaching a red light, a bend or a roundabout. . On the motorway, eco-driving also encourages observing a relatively low average speed, in order to reduce aerodynamic friction which increases exponentially at high speed.

On a Marseille-Paris journey, for example, in principle, driving at 130 km / h on the motorway should be avoided to reduce fuel consumption as much as possible. So when Audi offers different crews to make this trip at the wheel of the new fourth generation A3, the conditions are perfectly ripe to organize an interesting experience: how much does it cost to drive “fast”?

Time or money?

We each set off with an Audi A3 TDI S-Tronic, equipped with a 150 horsepower 2.0-liter turbo four-cylinder diesel mated to a seven-speed automatic transmission. With a mixed consumption announced between 4.6 and 5.0 liters per 100 kilometers depending on the options according to the WLTP homologation standard (sold from 34,050 €). Very quickly, the other crews settled into a rhythm ideally calibrated to reduce consumption as much as possible: maximum 90 km / h, adaptive regulator deactivated to avoid any loss of efficiency during automatic braking. But not us, who remain at the maximum authorized speed limit (in GPS speed). Given the length of the journey (770 km) and the capacity of the tank (50 liters), it does not include any refueling but only a quick lunch break. We will logically arrive before the others, but will consume more.

16.5 € lost but two hours gained!

Leaving Marseille at 8:00 am, we arrive at our destination in Paris at 4:30 pm. The on-board computer indicates 5.0 liters per 100 km for the entire trip, or 38.5 liters of diesel. Our “competitors” who started at 90 km / h will arrive two hours later, with a very nice 3.4 l / 100 km displayed on their on-board computer. That is 26.18 liters of consumption for them on the same journey. The difference in consumption is 12.32 liters, a gain of € 16.5 with a diesel at € 1.34 per liter. This demonstration perfectly illustrates two things: a modern compact diesel remains unbeatable in terms of pure consumption on a long motorway journey, and eco-driving really makes it possible to save fuel by polluting less. But experience also reminds us that on a long journey of this kind, it has a very big influence on the duration. And it asks a fundamental question: are two hours of your day worth less than 16.5 €?