does driving at a constant speed (pressing the accelerator constantly but with varying amounts) give better gas mileage or does getting to a certain speed and coasting for a while before pressing the accelerator do better? Why?

Question

I feel like the first one should do better, but I don’t get why, and while I’m driving I keep thinking the second version will somehow end up better – but how do hills affect this?

In: 3

Answer 1

Staying constant is going to be the best bet all other things removed.

In an automatic vehicle, Losses in the drivetrain and increased engine load make coasting and accelerating less efficient.

In a standard, slowing down causes the engine to lug, forcing the computer to put more fuel into the engine to keep it going. If you shift into a lower gear, you negate any winnings you may have got by going slow at the time.

Alternatively you can accelerate up to a speed, shift into neutral, and coast for a while with the engine at idle. Some jurisdictions have made operating a vehicle not engaged in a gear illegal, as it is unsafe and may make a vehicle less manoeuvrable. IANAL your gas mileage may vary.

Generally you save the most fuel by accelerating normally and evenly and keeping a constant speed. Not by floring it everywhere.