I found this interesting question from HowStuffWorks.com, as it tried to explain how to figure this part of owning a Hybrid out.
It forms part of the motivation and value-proposition of hybrid vehicles and might help you make up your mind if it is for you or not.
One of the tips to increase gas mileage is to travel at a constant speed.
The question is, what is that magical speed that will give you the most out of your fuel.
To explain this we must know how much power it takes to push a car down the road. The power required is explained by the following equation:
road load power = av + bv2 + cv3
The letter v represents the velocity of the car, and the letters a, b and c represent three different constants:
* The a component comes mostly from the rolling resistance of the tires, and friction in the car's components, like drag from the brake pads, or friction in the wheel bearings.
* The b component also comes from friction in components, and from the rolling resistance in the tires.
But it also comes from the power used by the various pumps in the car.
* The c component comes mostly from things that affect aerodynamic drag like the frontal area, drag coefficient and density of the air.
This equation says that if you double your speed, you will increase the power required by much more than double.
A hypothetical medium sized SUV that requires 20 at 50 mph might require 100 horsepower at 100 mph.
By plugging some speeds into the equation we can see how a 1 mph increase from 2 to 3 mph compares with a 1 mph increase from 50 to 51 mph. To make things easy we'll assume a, b and c are all equal to 1
Speed
|
Equation
|
Result
|
3 mph
|
3+32+33
|
39
|
2 mph
|
2+22+23
|
14
|
Power Increase
|
25
|
|
51 mph
|
51+512+513
|
135,303
|
50 mph
|
50+502+503
|
127,550
|
Power Increase
|
7,753
|
|
If this is a major concern of yours when selecting or opting to buy a Hybrid, bear in mind that purchasing is only half the equation. Using and maintaining the vehicle and on-going responsibility. Driving it as such to get the maximum benefit from the hybrid technology also important.