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This article is from the Motorsport FAQ, by A H Henry bspahh@midge.bath.ac.uk with numerous contributions by others.

31 Aerodynamics (1994 IndyCar Specifications)

Andy Brown from Galmer gave Racecar Engineering the following figures
for the Galmer G92, the car which won the 1992 Indy 500.

                Downforce  Drag      L/D    Cd    Speed for measurements
Short Oval      3460 lbs   1310 lbs  2.64  1.397  165 mph
Street Circuit  3040 lbs   1070 lbs  2.84  1.141  165 mph
Speedway        2835 lbs    972 lbs  2.92  0.669  220 mph

Fuel consumption is higher on a street circuit such as Long Beach
than on a short oval such as Phoenix: consequently the car has to be
set up so that it pulls less drag.
By way of comparison, in the days before cab roof fairings, a Cd
figure of 1.0 was typical for a high-drag truck. These days trucks
are down to the region of Cd = 0.6 The figures quoted for the 1991
Indy 500 winning Penske PC20 in speedway trim were 3010 lbs downforce
at 220 mph with 1075 lbs drag (Load/Downforce, L/D, = 2.80)
Brown commented: `I'm always a little cautious of comparing figures
from different wind tunnels because experience has shown them all to
vary slightly. The L/D figure is usually close though, and I'm
pleased to see that ours is better than that quoted for the PC20.
Provided we're both telling the truth, that is !'
Note: The downforce is approximately double the weight of the car,
so the car could drive upside-down with a suitable bit of road.

 

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