From Pat Symonds' tech column in F1 Racing magazine:
Pat Symonds wrote:When engineers refer to points of downforce, what do they mean?
When we discuss downforce or drag, we try to normalise results so that ambient conditions are irrelevant. If we simply talked about how many newtons of downforce were produced at, say, 200mph, this would vary between a hot day when air density is low, and a cool day when air density is high. Aircraft pilots know about this and adjust take-off speeds depending on ambient conditions as the lift their craft experiences also varies with temperature and air pressure.
To eliminate this ambiguity, we express downforce by means of a term we name the "lift coefficient." Of course, since it is downforce we are interested in, the number is negative. This coefficient is a number that, when multiplied by air density and the square of the speed as well as a reference area, will tell us the actual downforce. The reference area is generally the frontal area of the car but, although many teams express this as 1.5 square metres, there is no hard and fast rule and so the way one team expresses the lift coefficient may be slightly different to another.
Let's say a car has a lift coefficient of -3.50. The gains made in the windtunnel will often be of a magnitude shown only by the second decimal place of that coefficient and, for convenience, aerodynamicsists talk about this being a point. Therefore if we improved our downforce by one point we would increase the coefficient from -3.50 to -3.51. In fact, downforce gains are so hard to come by that we often use the third decimal place as well and this increment is termed a "unit."
So a point is really nothing?
It's true that it is a small percentage and the effect of a gain of one point will vary from circuit to circuit, but, as a rule of thumb, a gain of three points will represent a lap-time improvement of 0.1 seconds. Given how close racing is these days, that can be very significant.
