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Discussion Starter · #1 · (Edited)
So any time someone asks about gas mileage in their TJ, someone inevitably replies with the "you have a brick on wheels" comment. This got me thinking, "How does a TJ actually compare to your run of the mill masonry brick when it comes to aerodynamic drag?"

Well I did some research and then some math and the results were interesting. Please take into consideration this was done for fun and I made assumptions when I needed to.

First I found the formula for aerodynamic drag. Which is:

F(d) = -.5pv(^2)AC(d)

Where

F(d) = Force of drag in Newtons
p = density of air in kg/m(^3)
v = velocity of the object in m/s
A = Area of the face of the object
C(d) = drag coefficient (typically determined experimentally)

I determined the density of air and the velocity would be constants

p = 1.168 kg/m(^3) (which I found here)
v = 65 mph or 29.0576 m/s (using this conversion calculator)

Then I needed to determine the Area of the front of a TJ as well as its drag coefficient. Luckily, I found both here.
A(Jeep) = 2.58 m(^2)
C(d)(Jeep) = .58

For the brick, I realized I needed to scale things up considering a standard brick is much much smaller than a TJ. I compared the width of the TJ to that of the brick and used that as the scale and simply multiplied from there. So...

A(Brick) = .965 m(^2)
C(d)(Brick) = 2.1 (found here)

So after that it was just some simple multiplication.

F(d)(Jeep) = -.5(1.168)(29.0576^2)(2.58)(.58)
F(d)(Jeep) = -631.738 Newtons (at 65 mph)

F(d)(Brick) = -.5(1.168)(29.0576^2)(.965)(2.1)
F(d)(Brick) = -999.261 Newtons (at 65 mph)

So... technically, a TJ is a more efficient than a brick, but not by much. So while, there is obviously some exaggeration in saying the TJ is a brick with wheels, it's not that far off.

This was a fun little exercise. My wife thinks I'm even more of a geek now, but hey, it beats watching reality TV. :D

Edit: Realized I forgot to square the velocities in the original calculations.
 

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:laugh: :laugh: :laugh: :rtft: :rofl: :rofl: :rofl:

i couldnt stop laughing when i read this good stuff though. i like that now i can use this simple explanartion when i am trying to convince someone new to the jeep world, this will help us out now that we know it is better than a brick on wheels. maybe we can get more new owners here.:D
 

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What!?!

You need a hobby, a girlfriend or something!!!:laugh: :rofl:
 

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:laugh: :rofl: :D :brickwall
 

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That's something I should do for Physics class as an extra credit assignment...too bad I'm done with physics. :D

good reading, makes me feel a little odd thinking I drive a large-scale near-equivalent to something that a house is made of. At least I feel safe in it....:p
 

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I always compare my TJ to a filing cabinet with the drawers hanging open...
 

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:laugh: Geek...Just kidding :laugh: . I knew someone was going to do that someday.:wave:
 
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