On level ground and for a given power, the maximum speed is usually set by the drag produced by the air flowing past the car. This is given by
where v is its speed, A its frontal cross-section area.
is the density of air (), and
is a coefficient that measures how
slippery the car is. Typically, .
In these calculations, we've assumed that the maximum power is delivered at any speed we like. In part II, we'll see that the power produced by the engine in fact depends on how fast it spins, so these calculations only work if we choose the ideal set of gear ratios to match the maxium speed and engine revs.
F1 racing cars tend to have very high values of , because they use spoilers to push the car down onto the track and increase its cornering speed. We'll cover cornering speed in Part IV.