Owner's Manual

1110
Differences in Metric
There are many detail differences
between the US and Metric modes. We’ll
review the differences here.
•
Speed is measured in kph.
•
Vehicle weight is measured in kg, and the
default weight is 1600 kg. You can adjust this in
the setup mode. (See pages 24-30 in the Owner’s
Manual).
•
The braking test is from 100kph to 0. To perform
a braking test, start a timed run as usual, then
accelerate to at least 105 kph (but no more than
130 kph), then immediately perform a braking
test. The results will be included as additional
items added to the standard acceleration run data.
•
Rollout distances for the timed runs are measured
in cm, and adjustable from 0 to 65cm using the
setup mode. (See page 29 of the Owner’s Manual
for a definition and detailed discussion of rollout).
•
Aerodynamic drag CDA is measured in square
meters. You’ll need to enter this value in the setup
mode in order to calculate horsepower for your
vehicle.
See the following section for details.
3
Calculate your vehicle’s CDA
You can determine the correct CDA number by using a
“coastdown” test.
• On a flat road, on a day with no wind, accelerate
to slightly above 100 kph.
• Put your car in neutral (whether your car has an
automatic or manual transmission, it is important
to put the car in neutral).
• Measure the time it takes your car to decelerate
from
exactly 100 kph to exactly 80 kph.
• Perform this test at least three times in each
direction, to make sure your results are relatively
consistent.
• Average your times, then use the table to the right
to determine the CDA factor.
• Multiply your car’s weight times the CDA factor
from the table to determine your car’s CDA.
EXAMPLE: Find the CDA of a 1800 kg car that takes
20.5 seconds on average to coast from 100 to 80 mph.
Look at the table. For 20.5 seconds, the factor is .000382.
Multiply that times 1800 kg to get the car’s CDA.
1800 x .000382 = .69
.69 is the car’s approximate CDA.
Multiply your
car’s weight by
this number to
calculate your
CDA.
13.0 .000798
13.5 .000756
14.0 .000717
14.5 .000681
15.0 .000647
15.5 .000615
16.0 .000585
16.5 .000557
17.0 .000531
17.5 .000506
18.0 .000482
18.5 .000460
19.0 .000439
19.5 .000419
20.0 .000400
20.5 .000382
21.0 .000365
21.5 .000348
22.0 .000333
22.5 .000318
23.0 .000303
The average time
it takes your car
to coast from
100 kph to 80 kph
(in seconds)
To determine the metric CDA of your car:
There are three ways to determine your car’s CDA:
• Find specifications for your car’s CDA
• Estimate your car’s CDA
• Calculate your car’s CDA using a coastdown test
Details on each method follow.
1 Manufacturer’s specifications or other research
Very rarely do manufacturers list the aerodynamic
qualities of their cars, unless they are exceptional. Try
searching the internet for the terms “drag coefficient”
or “frontal area” and the make of your car.
Note: If you find specifications for US cars they
list frontal area in square feet. Divide those figures by
10.76 to convert to square meters.
2
Estimate your vehicle’s CDA
Use these examples to estimate your car’s CDA.
Honda Insight .25 CD x 1.90 M
2
= .48 CDA
Corvette C5 .29 CD x 1.98 M
2
= .57 CDA
Porsche 911 .32 CD x 1.80 M
2
= .58 CDA
Audi S4 .31 CD x 2.04 M
2
= .63 CDA
Honda Civic .34 CD x 1.95 M
2
= .66 CDA
Minivan or SUV .40 CD x 2.80 M
2
= 1.12 CDA
Pickup or van .45 CD x 3.25 M
2
= 1.46 CDA
Modern passenger car CDs are usually .30 to .35.
Van, SUV and truck CDs are usually .35 to .45.