Quote:
Originally Posted by thecheese429
The coastdown tests did not show improvement, oddly enough. I lost 9 mph in the first 10 seconds instead of the 6 from last night. I did not record the temperatures yesterday/tonight, so I am sure that is the problem. Or not. Whatcha think?
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How low is the front air dam? If I understand 'this all' correctly it only needs to be slightly lower than the lowest protruding part underneath your truck.
What could've probably happened with the side-skirts added, was that the pressure under the truck became much lower than pre side-skirts when air could leak in again from the side even though you had the front air-dam.
With just he front skirt, it helped clean up what happens at the front but still allowed for the lower pressure to be re-filled. Thus the low pressure at the back of the truck that will occur normally at speed was just about the same as normal.
With the side-skirts added however, you might actually have helped create a much lower pressure [and bigger vacuum area] at the back than it would normally be and this actually put you back to square one [kind of]. I could be wrong about the cause, BUT I also agree that air temp will definitely affect the readings.
I will add that you must remember not to add to the total frontal area and hence increase the air you need to displace. I think the problem with [some] pick-ups are that many times all the blocking and smoothing and covering that needs to happen underneath to get it car-like might be good for Cd, but bad for Frontal Area and finding the balance for what happens under the truck becomes much harder than for a car with an underbelly that's almost flush already.
-like I said, if I understand this all correctly.