Section 5 - Vehicle & Chassis Performance

The total force required to push a vehicle at speed is the sum of the aerodynamic drag and the rolling resistence.  The power required is the total force times the velocity. 

             FTotal =  FDrag + F Rolling Resistence

             PTotal =  FDrag•v + F Rolling Resistence•v

             P = (ref p•A•Cd•v2)•v + r0•v

where;             FA = Air drag in Newtons, (force)

            p = Density of air = 1.23 kg/m3

            A = Frontal area in square meters

            Cd = Drag coefficient

            v = velocity in meters/second

For the GM Impact, power, as a function of velocity, is:

      P =  ½•(1.23 kg/m3)•(1.58 m2)•(.19)•v3 + (9,790 N • 0.0048)•v 

At 60 mph or 100 kph;

       P = 4,052.8 + 1,315.8 = 5,368.6 N•m/s = 5.368 Kw

The power require as a function of velocity goes up with the cube of the velocity.  This graph illustates this fact for the GM Impact.

The energy consumed for a vehicle to travel is a function of the power being consumed over a period of time or the force over a distance. 

                        Energy = power•time = force•distence

From the information above, the GM Impact require 5.368 kilowatts at 97 kph (60 mph).  In one hour the Impact would consume 5.368 kilowatt•hours, kwh.  Also, the Impact requires a force of 193.65 Newtons to travel at 97 kph.  In one hour the vehicle will travel 97 km.  The energy consumed is 97,000m•193.65N = 18,784,050 N•m or 5.218 kwh.  So, whether the energy is determined by power and time or force and distence, the results can be very close.

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