So, we're trying to simulate an electric car running with a DC-engine. To get the calculations right we must determine the rolling resistance coefficient and airdrag coefficient. (We've already determined the rolling resistance to about 0.014, doing some linear calculations at low speeds < 2m/s, where the airresistance is ~ 0) We've gathered data of the deacceleration of the car (doing a runout test) using GPS data. This means that we have the speed as a function of time. However, no matter what we do, it seems that we get the calculations wrong, as we expect the rolling resistance coefficient to be somewhere between 0.010 - 0.020 and the air drag might be 0.3 - 0.9. Here is a graph of the speed as a function of time. http://dl.dropbox.com/u/202411/p2/runout1.png [Broken] The graph is generated with MATLAB using this data: http://dl.dropbox.com/u/202411/p2/v.txt [Broken] , notice that this is just the speed, however, we sample 5hz, which means Δt = 0.2s between each datapoint. So, how do we calculate the correct airdrag- and rolling resistance coefficient, preferably with the lowest possible error?