GMT 400s were the first truck to be desinged in a wind tunnel. That being said, I would think the valance was added because they were trying to prevent drag from the undercarriage, but that is just a guess.
Disclaimer: Links on this page pointing to Amazon, eBay and other sites may include affiliate code. If you click them and make a purchase, we may earn a small commission.
True enough, but they do well at speeds over 100 MPH. They don't float at high speed at all. I turned off my speed limiter (or set it to max,,228 MPH when I tuned my truck) , and have had mine well over 100 MPH more than once. Like I said, the valance has been off of mine for years, well before I reset the speed limiter. I was very surprised how well the truck handles at high speeds. After doing some research, I found out that these trucks were the first to be built in a wind tunnel.These trucks are fairly close to the aerodynamics of a brick. I'm not too worried about it
The valance has nothing to do with cooling the radiator. You are correct about the air moving across it, and what air the fan pull across the radiator at low speeds and when stopped. My valance has been off of my truck for years, and it never over heats, even in the hot south Louisiana summers.
the valance does indeed reduce the drag coefficient. at least on the stock height trucks....thereby helping with fuel economy. GM first introduced them on the 2nd generation face-lifted trucks in 1981(the "squares"). same "air deflector" was used through 1991......my 1986 had it and that promptly went in the dumpster.
i check my fuel economy every tank, yea i'm stupid like that....been like that forever.......anyway, when i got my new(to me) '98 it came to me with the lower valance.....after i removed it i found out i had kept loosing 1-1 1/2 highway mpg's thereafter........
i do know that if you put a roof roof rack with 4 Hella 220's on a Jeep Cherokee you'll loose the same 1-2 mpg on the highway.
on lifted trucks with larger tires, etc there's no difference.........gearing DOES play a roll, but all things equal, it's for fuel economy. tell your friend to stop spreading misinformation...........or you could slap him as others suggested.
nothing helps in city bumper to bumper traffic, but my long distance driving IS important to me so i'll be putting another air deflector back on, probable on with good fog lights in it......may as well make it useful too.