I cracked open my copy of Race Car Vehicle Dynamics (R146) by Milliken and found something very similar to the example I made in my article Aerodynamic Coefficients: Lift. Let’s take the data from Milliken’s example and see if my method gets the same outcome.

In his book he states the Chaparral 2J has:

Tire Friction Coefficient: 1.3

Weight: 2500lb

His example is simpler than mine so I can start halfway through my earlier example.

$F=m a=(2500*.4536)*(1.7*9.81)=18,912N$

$F=\mu N$

$18,912=1.3*N$

${NormalForce Required}=14,548N$

${Downforce}=N-W=14,548-11121=3427N=770.4lb$

His book says the downforce was 770lb. Looks like it works!