When I first started driving I drove slow bc I thought it would save gas, then I started driving faster when a friend told me you use the same amount of gas whether you drive slow or fast (as long as it’s the same distance), you just would be driving fast for a shorter amt of time and driving slow for a longer amt of time, but at the end you burner thru the same amount of gas. Is this true?
In: 5
It’s very vehicle dependent. It’s related to engine efficiency at a given rpm, gearing, drivetrain efficiency, drivetrain harmonics, rolling resistance, aerodynamics, and how all of those interact. BUT. In general, your greatest efficiency will be at the lowest engine speed to provide enough power to keep you moving under light engine load in top gear. For most cars, that’s targeted at about 50-70 mph, depending mostly on gearing. This will vary depending on a number of factors. For instance, you can run a large displacement naturally aspirated engine at around 1800 rpm and make plenty of torque to keep the vehicle moving on the highway, so you can target that engine speed at that ground speed in top gear to theoretically yield greatest economy. Whereas you’d target a higher engine speed with a smaller engine where 1800 rpm is too low to provide adequate power to maintain speed. So in theory, slowish speed in highest gear is going to yield your best economy, as aerodynamic drag is the biggest factor, and it increases exponentially as speed increases. But you will get weird pockets of efficiency. For instance, I used to have a 2006 Mustang GT. It was definitely targeted to run about 65. That was about 1900 rpm in 5th gear. That would yield around 24 mpg highway. But if I ran it at 80, around 2300 rpm in 5th, it should have been worse due to higher engine speed and aerodynamic drag. But it ended up yielding 27-28 mpg consistently. Apparently the drivetrain harmonics were just happy and efficient there.
Latest Answers