Thursday, June 11, 2015

Tips for Getting Better Gas Mileage

Gas is back on the rise. (The subsidies ran out, it happens every year.) So I wanted to pass on a few driving tips to help you make the most out of your precious gallons.

Accelerate at a constant moderate pace, between 1500 and 3000 rpm is your target range. Your engine is more efficient under these loads and you will get better gas mileage if you acceleration is smooth and swift. After you go above 40mph or so, the air resistance generated by the vehicle is the greatest force influencing gas mileage. Think about running through a body of water, you are working significantly more to move yourself through. Is the resistance similar to when you stick your arm out the window at 70 mph? The air is a fluid just like water, albeit much less dense.

The problem is that the molecules of air are in the space in front of your vehicle. In order for your vehicle to move forward into that space you need to get all of the air in front of the vehicle to move as far as it needs to go, to get to the sides of the vehicle before you drive through it.

So at 70mph you have to move a lot of air really really fast, and that takes a lot of gas.

Next we need to think about newtons laws

1: An object in motion will remain in motion unless acted upon
(air molecules are easier to move when they are already moving)
2: Force=Mass x Acceleration
(the force it takes to move the air is equal to its mass times its acceleration)
3: For every action there is an equal and opposite reaction.
(When you push the air out of the way in front of you, a vacuum is created behind you as the air rushes back into the space behind your car)

When the air molecules in front of you are moving, it is easier to move them. Air has six cardinal directions that it can go. (Up, Down, Left, Right, Forward, and Backward) Everything but backward is beneficial to your gas mileage. So you have a one in two chance of getting a gas mileage benefit. (if the air is moving backwards and left, it is still pushing you back.

Think about the space behind your car after you move through the air. Because of the vacuum, air is rushing in from everywhere to fill the void. Because your vehicle is moving forward, the air rushing in rarely gets an opportunity to go backward. So when you are following behind someone, their air is rushing all around already moving pretty quickly from their car.

It takes much less energy to move the air around your car if it is already moving from their car.


That being said a safe distance to follow is two seconds at highway speeds.

Vehicles that take up more frontal/rear surface area (Vans, Box trailers, etc...) have to move more air, which means better gas mileage for the people behind them. If you drive in a chain with multiple cars you get better gas mileage. (Remember trucking convoys? They saved gas which would allow them to speed and get more dollars per hour for the same amount of fuel.)

So whenever you are out driving, get behind someone, or get someone behind you, or both! CONVOY!

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