Calculator: Determine Horsepower @ specific speed
 

I put this excel file together a while back after reading an article on Autospeed called Real World Measurement of Drag and Lift. He had a calculation to measure Cd. I was more interested in reversing the calculation to get horsepower at a specific speed, so I made a calculator. The downside is that it does not take into account rolling resistance.

To use it, you will need the Cd of your vehicle, length and width (or just frontal area), and input a speed.

Horsepower at Speed Calculator

Interesting.

Daox, here is something I got a couple years ago from an RV forum. It was made not necessarily for saving fuel, but for estimating if you had enough engine power to tow the trailer depending on expected grades, speed, and wind. Im not sure of the accuracy of any of it though, you would probably know better.

I just look at a dyno graph to see what it is at an rpm and translate that to the speed in 5th gear :) may be a little off, but it works for me.(i get the dyno from guys who have done it with the stock version of my car online)

dyno graphs are only for full throttle. You aren't using NEARLY that much power to cruise.