Need some help

[mtbiker278]

Looking through the archives I found SVOboy's borrowed equation for calculating the rolling resistance and coefficient of drag, etc. The equation seems fairly simple enough and measuring the decceleration appears to be easy enough, but I still have some issues to resolve.

1) Finding a reliable Cd number for my car!
The civic hybrid has a Cd of .28, but my car is the coupe which has a steeper windshield rake (21 rather than 23) and is shorter by 2 inches. Plus the body panels are quite different so I'm sure that has some affect.

2) Finding the frontal area of my car
I'm not exactly sure what frontal area entails. The front most part of the car? (front bumper, headlights front part of the hood) or something different.

My ultimate goal is to have a giant spread sheet with speed, rolling resistance, drag and whatever other properties (air density, temp, ect) so I can figure out at what general speed my car is the most efficient.

I have a 2006 civic coupe ex auto. Gas mileage numbers are going up slowly as the car breaks in. I'm at around 4.5k miles so far after buying it in Feb.

On a side note, does anyone know what incriments the newer honda ecus modify the fuel map by RPMs. The reason I ask is currently I cruise at 55mph @ 1750rpm, but increasing to 60mph @1950rpm isn't that much higher.

So help would be awesome, thanks!

[thisisntjared]

those numbers are somewhat fudge-able the front area is around 2.2-2.5 square meters. i bet the cd is between .27 and .29 so use both of those as your upper and lower bounds.

the incriments in rpms for adjusting the fuel are continuous in newer hondas and self-adjusting(over time) to 20% depending on o2 sensor readings.

[MetroMPG]

Originally Posted by mtbiker278

I'm not exactly sure what frontal area entails. The front most part of the car? (front bumper, headlights front part of the hood) or something different.

it's the "projected" area of the car. back your car against a theoretical wall which is perpendicular to the setting sun. when the sun reaches the horizon, trace (quickly) the outline of your car's shadow on the wall. that's its frontal area. (actually doesn't matter whether you back against that wall, or drive up to it - identical shadow.)

or, there's a quick'n'dirty method for calculating it, which is height x width x .8 (not sure if that's width with mirrors or without though).

[mtbiker278]

Thanks for the info. I'll probably end up buying a scan guage eventually, but this should help for the time being. Gas just hit 2.95 in my area and is like 3.15 down in DC. Feelin the hurt!

[SVOboy]

Go for the scangauge, instant FE numbers rock my world!