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Theory Of Testing
Volume 2, 9/10/04
Section 8 - Page 11
8.5.1.2 STP
The STP (also called STD) standard is another power correction standard determined by the SAE.
This standard has been stable for a long time and is widely used in the performance industry.
Power is corrected to reference conditions of 29.92 InHg
[101.3 kPa] of dry air and 60 F [15.5 C] .
Because the reference conditions include higher pressure and cooler air than the SAE standard,
these corrected power numbers will always be about 4% higher than the SAE power numbers.
This is the default correction used on AutoDyns.
8.5.1.3 ECE
The ECE standard is based on the European Directives. Power is corrected to reference
conditions of 99 kPa [
29.23 InHg ] and 25 C [ 77 F ].
8.5.1.4 DIN
The DIN standard is determined by the German automotive industry. Power is corrected to
reference conditions of 101.3 kPa [
29.33 InHg ] of dry air and 20 C [ 68 F ]. With the advent of
European legislation and standards, national standards such as the DIN (formerly widely used) are
now less significant.
8.6 Aerodynamic Power
FAxCd (Frontal Area x Coefficient of Drag, Channel 78), of the standard CycleDyn and AutoDyn
configuration files is used in the Road Load automated test to simulate aerodynamic drag at any
road speed up to the maximum speed of the vehicle. The charts below are provided to help you
determine the proper value to enter in this Specification channel. There is a chart for US units and
one for Metric units.
The easiest way to use the chart is to have a maximum corrected wheel power number for your
vehicle.
Wheel power can of course be obtained easily by performing a power run on the dynamometer.
The maximum speed the vehicle can reach on the road can be estimated or assumed (for
unmodified vehicles, the manufacturer’s rated top speed can be used).
On the chart, power is on the Y-axis (left), and speed is on the X-axis (bottom). The graphs
themselves represent the power needed to reach a given speed for a given aerodynamic drag
(FAxCd).
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