Quote:
Originally Posted by htvfd460
On a 2.3% grade was my test. I gues I should have worded a bit differently. Terminal velocity is what I am looking for. (my T.V. Went up a little over 15 MPH. From 65 to over 80, with the cops in NY I didn't want to go further and get another ticket)
I did a 4" frront and 5" rear drop. Later because of chewing threw fender wells I added a 1.25" rubber isolated from a Superduty (with modifications). I went from stock avg 16-17 mpg all the way up to 20-23 mpg. (also tuned and k&n air filter) from about 300 miles per tank to over 400 miles per tank. My wallet gives me little kisses every night.
With the overall ride height I don't remember what the exact numbers were but with in a range of +- .25". I only really paid attention to the ride height while experimenting with + and - sized tires. Then back to stock. (it's nice having other vehicles to use for swapping rims and tires.)
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On a constant 2.3% grade it would be the vertical vector component of the gravitational constant ( 32.3 ft/sec/sec ( 9.81 m/sec/sec)),factoring the vehicle mass and rolling-resistance,along with the air drag providing all the force to just balance the force due to gravity.
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* By lowering the truck you've altered the frontal area a bit and you could calculate the difference by subtracting the amount of tire face which is now shielded within the body due to the drop.
* You haven't altered the mass so that's a constant.
* the grade is the same so the push from gravity can be taken as a constant.
* The tires need to remain unchanged for at least one back-to-back data set or it will enter another variable into the mix.
* Total weight needs to remain constant.Same gear on board each time.Maybe a full tank each time as each gallon is about 6-pounds and directly affects momentum/inertia( the heavier truck will have a higher TV).
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*( from Hucho ) For top speed,velocity will vary at 10% additional velocity per 30% drag reduction.
If say your new TV is 80 mph vs 65 mph for that particular gradient,then 80/65= 1.23,or,a 23% velocity increase at 'fixed-power'.
23%/10% per 30% drag reduction = 2.3X 30= 69% drag reduction.So this suggests that only 31% of the original drag remains.
If the Ranger started at say Cd 0.45,the formula suggests that the drag was cut to Cd 0.139,if frontal area was unchanged.That's pretty low!
That's a very simplistic look at the Ranger.
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I hope you have a baseline for mpg without mods.If you'll track your fuel use maybe we can back-engineer your change.
10% delta-Cd = 5% delta-mpg @ 55 mph
10% delta-Cd = 6% delta- mpg @ 70 mph.
