Dodge ram 4x4, cleaning the underbody airflow...
 

I have a 2005 Dodge Ram 2500 diesel 4x4, 3" lift, 285-75-17's (34"). I'm looking for input on a few ideas I have for cleaning up the airflow under the truck. I know dropping it back down will get me about 1~1.5 mpg back that was lost when I leveled it so that is a possiblility later on down the road. For now, I'm looking to be able to get up into the 20mpg range with the existing suspension & tires.

With that said... ideas I have seen other trucks (ford f150's) with a 2nd air dam behind the 1st one that extends down another inch or two. One of the ideas I have is to build a secondary air dam similar to what they have and set it up so it mounts to where the steering stabilizer mounts (this mounts under the swaybar mount and supports the sector shaft on the steering box). I'm thinking of taking a long straight rod and extending it from the bottom of the existing air dam down to the axle and find out how much I could drop it down without impacting the front approach angle too much.

Second idea is to put a small air dam in front of the tires, front & back (front airdam does not cover enough I think....) I've seen this done on the underside of cars and think it may have a benefit to the ram. I'd also considered putting a couple farther forward that would be angled some, similar to what the big rig trailers are now doing but not as obnoxious.

Lastly I'm wondering how well airtabs would do on the underside of the rear bumper and on the frame. I realize they need to be spaced @ 4/ft and there probably isnt a whole lot of room on the back bumper and or hitch and obviously I could only get 1 across on the frame rail.

One of the goals here is to make it so it is not overly obvious all of the mods are on there.

Feedback?

Oh yeah, great forum!
Also, before it is said, I already have a tonneau cover which drops my mpg. I have another that is a rollup canister type that I plan on putting on and will be adding the rear tailgate spoiler at some point down the road. I also have engine compartment mods I plan on but that discussion is for another forum thread :D

also, I'm at about 17.5 mpg before putting on the current wheels & tires, they dropped the rotating mass by 9#/wheel and tire height was increased by 1"

Ram
 

Since it's a Dodge,you might look at the 2013 Ram 1500 for ideas.This new 1500 has the lowest Cd (0.36) of any production pickup.They do use active,air suspension to lower the truck for highway duty but you might see some cleanup tricks they did.
Having the front airdam as low as your lowest undercarriage components will help shield oncoming air from colliding with those bits and pieces and also all the tire faces.
If you could do rocker panel extensions or 'running boards' as low as the airdam,flush with the outsides of the tires,it would provide a surface to hold the air alongside without turbulence.
And these would net you some of the benefit of a full belly pan.
Closing up all the gaps around the wheels are a source of drag reduction as well as full wheel covers.I realize it doesn't 'fit' the 'image' of a 4X4,but it does cut drag.
Wheel skirts can also be part of your under-body flow management recipe.
Also,cooling and air conditioning air dump into the under body region,so some grille blocking could be part of the drag reducing equation as well.The grille opening on my truck represents only 1/12th of the radiator's surface area.

thanks for the feedback... I looked at the front end and there is room for improvement. The bumper has about a .5-.75" gap that is open and probably causing a problem. I noticed that around the headlights there is a seal that preents air from getting past it. I would take that as an example on what to do with the bumper. I believe should be able to push the bumper up a bit to close off that gap. Looking at other rams I think mine is a bit lower than what it should be. I had the bumper of years back for a tow hook install.

so you think the 2nd air dam is a waste? I also looked at the possibility of the smaller deflectors off the frame and that should be do-able...

2nd dam
 

If you had the front airdam done,and the rocker panel bottoms matched that of the airdam,you'd be dragging an inverted pool of dead air around under the truck,with energetic flow down beneath it.
The 2nd dam would be entrained within the dead air mass and not really in a position to to affect the flow.In a crosswind,the air would 'see' the outside edges of the second dam,and unless it had generous outer edge radii,it could trigger flow separation which otherwise would not exist,aggravating the wake.
If it were me,I'd be looking at a belly pan.Trucks have the worst under bodies and respond the best to paneling.

Bump

Not so much a bump as a resurrection.

... I saw a full-sized pickup truck passing me on the freeway yesterday (I was doing 5 over the limit) with his tailgate down, likely to get better fuel economy. The guy is going out of his way to reduce fuel economy.

So he’ll re-read what Phil wrote.

The top of the 2nd air dam is in line with the bottom of the OEM one. Slowmover one of the things I'd considered trying was to take that V2 of the air dam and change the ends some to control how the air flows off of it. I think that is part of the reason that one created more drag vs the V1 of the air dam.

Freebeard that v1 air dam is just a flat piece mounted under the swaybar. Its currently angled to direct flow towards the ground at a decent angle. Before the front grill block it was probably generating a slight lift.