Lower Valance

Well my wife finally decided today (own her own) that the lower valance on the front bumper needed to go. Needless to say I did not argue and it looks so much better.

I still don’t understand why they put these on in the first place. To me it looks like it will cause wind drag.




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I believe its an air skirt, it directs the air flow for better hwy mileage.

Correct, it helps minimize the turbulence under the truck. This equates to a more stable ride and improved gas mileage at highway speeds.

They are believed to be quite effective, and I have heard rumors of a 1 mpg or more difference at highway speeds. It is probably exponential, so the faster you go, the more mileage you will lose. TTBOMK, the FX4 has a more truncated version. I do not know the degree of one vs. the other, but eventually I will remove mine, and add it for longer highway trips.

I just don’t see how they are fuel efficient. It would be different if they curved back some instead of being a flat wall, plus it just looks stupid on the front.


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Gas mileage.

dlcorbett said:

I believe its an air skirt, it directs the air flow for better hwy mileage.

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This is false. IF there is a loss it’s about .001 mpg stop telling lies please

Robert McMillan said:

This is false. IF there is a loss it’s about .001 mpg stop telling lies please

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Where is your 4th gen much less data proving this random number you pulled out of your ass? You accuse others of lies to insert your assumption? C'mon...

It's definitely not for esthetics.

The extensive wind tunnel and real world scientific testing by auto manufacturers necessitated the need for it to maximize airflow for better efficiency. All vehicles, going back decades, have some variation.

I personally hate how it looks.

Removing it will have some minor effects on gas mileage. Just like disabling the engine auto-stop/start feature.

Every little bit helps the auto companies meet EPA standards. It's a balancing act. Multiply small gains in MPG over thousands of vehicles and there's the main reason.

Robert will deny and argue like crazy, but it’s a fact and just plain engineering. References are all over the place, same reason a lift decreases mileage. Ask any engineer or plug some info into a wind tunnel software or better yet a real wind tunnel. Dave is correct that it’s exponential the faster you go, or if you have a strong headwind. It could be upwards of 1 mpg at 70+ mpg, but I don’t have specific data on the Expedition nor access to the software personally. References below should be good enough, the Expedition would see higher gains that these examples. Either way, question is does it matter to you. I’ll be pulling mine off soon, debatable if I’ll install it for long trips.


https://www.verus-engineering.com/blog/cfd-cases-4/post/air-dam-or-splitter-a-closer-look-12

http://www.grandmarq.net/blaze/Blaze_Pics/AE 507 lect 7 Aero Drag of Autos.pdf
Reference page 17-19. On a VW Rabbit, air dam equates to .02 Cd.

https://commons.lib.jmu.edu/cgi/viewcontent.cgi?article=1271&context=honors201019
Reference page 44. 06 Range Rover Sport with a Cd of .68. I believe the Expedition is around .39? Front air dam only decreased drag 14.5% or .1 Cd. That’s a substantial decrease