Quote:
Originally Posted by Vwbeamer
I think the Cd on my truck is .32.
.32, down from .39 factory, with just a half tonneua cover and lowering.
Using the Aerodynamic and rolling resistance tool, I figure my Cd is .32
Here's the variables I used-
Vehicle weight: 1950.4 kg / 4300 lbs
Crr: .008
Cd: .32
A: 2.7 m2 / 29.5 ft2-Down from stock 29.75
Fuel energy density (Wh/US gal.): 33557
Engine efficiency: .26
Drivetrain efficiency: .97
Parasitic overhead (Watts): 0
rho: 1.225 kg/m3
Varables that I know to be true-
Truck weighs >4300 pounds with me in it
Frontal area stock is 29.75
advertised Cd stock is .39
I took a 762 mile round trip, using 10% ethanol, 87 octane gas traveling @ 70-73 mph ( measured by GPS) I got 27.14 mpg.
Does lowering the truck decrease frontal aera more than just .25 sq foot? I figured that by less tire tread being exposed, because it's now further in the wheeel well.
So is my Cd really .32 now or I'm I tripping.
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My best guess is that (in your words) you're tripping.
I think you can basically ignore all the calculations (BS in = BS out) and just look at the magnitude of changes required on real, properly-measured cars to see that change in Cd.