NormalCalculation of Vehicle Drag Coefficient and Coefficient of
Rolling ResistanceTrials in Direction 1Trials in Direction
2timeV1V2V3V4V5V6V
avgseckphkphkphkphkphkphkph070707070707070.01kph=0.2777777778m/s1061606060616060.31mph=0.4444444444m/s2052525151525151.53044444343434443.540373738373737.537.350323232.53232.1602727.52727.2702222.522.3rho1.22kg/m^3density
of air (adjust for your altitude)g9.81m/s^2gravitational
constantA2.3m^2frontal areaM1000kgmass of vehicle plus
occupantstimeV actualV
modelFaError^2secm/sm/sNewtonsm/s^2019.4419.44299.80207292720.29980207290.00000517.9454340798270.73216273090.27073216271016.7616.5917732662246.48381925740.24648381930.028051515.3593541699226.06034573280.22606034572014.3114.2290524412208.71428069950.20871428070.005852513.1854810377193.87584804910.1938758483012.0812.2161017975181.10441901510.1811044190.017633511.3105797024170.05486561510.17005486564010.3510.4603053743160.45378420190.16045378420.01279459.6580364533152.0824023630.1520824024508.928.8976244415144.76409920540.14476409920.00068558.1738039455138.35516611660.1383551661607.557.4820281149132.73788008420.13273788010.00413656.8183387145127.81525160440.1278152516706.186.1792624564123.50700166640.12350700170.00000Sum
of Error^2 (minimise by changing Cd and Crr)0.06913Drag
coefficientCd =0.3696811693Coefficient of rolling resistanceCrr
=0.0105711271
What should be the velocity now based on the acceleration 5
seconds ago?
Normal
ActualModelTime [sec]Velocity [m/s]Vehicle Velocity vs Time
How to use this spreadsheet:1. In Cell B6, specify whether your
data will be in "kph" or "mph".
2. In Cells B7 through G14, enter the vehicle speed you recorded
at 10 second intervals as the vehicle decelerated in neutral.
Always start the clock (t=0) at the same speed (ex 70 kph). Do 3
trials in each direction on a flat stretch of road (Columns V1
through V6). Don't worry if you can't fill in the lower speeds on
some trials due to traffic. An average will be calculated based on
the available data.
3. In Cell B18, enter you best estimate of your vehicle's
frontal area in m^2.
4. In Cell B19, enter your vehicle's mass including occupants in
kg.
5. Using Solver (Tools/Solver...) set Cell F39 to a minimum by
changing cells F41 and F42.
6. Confirm that the "Model" line matches the "Actual" datapoints
in the graph.
7. Cells F41 and F42 now give the drag coefficient and
coefficient of rolling resistance for your vehicle.
8. Make modifications to your vehicle and repeat the test to see
if you improved things.
