Reclaiming MPGs on Lifted Expedition

[buffy]

So, I'm running LT275/60R20 Yokohama tires measuring 33.3". Factory fitment is around 32". I love the look, the LT construction and the minor lift. I don't like that the MPGs went from 16.5mpg to 14.5mpg. These tires are 10#s heavier, and of course, taller. So what caused the drop. Could be the weight, but I suspect air underneath the truck. Putting on our engineering cap and reading the interwebs, I confirmed how simple front airdam design works. So I didn't have any problem finding something I could add to the bottom to extend the factory one down.

I used this: Trim-Lok DD1201-25 EPDM Dual Durometer Rubber/Metal Carrier Flap Seal, Fits Edge 0.050" - 0.090", 0.925" Flap Length

This is made from a EDPM rubber. Super flexible. It can take a lick. Steel wire core.

You get 25' of it. It's expensive @ $64.20, so you might want to convince a few friends to give it a try with you. I used stainless #8 screws with painted black tops to secure them to the HDPE air dam. The seal goes on good and tight, but you need the screws to keep it on if you drag over something.

The results? 16.0mpg

I didn't get all of it back, but enough to make this worthwhile. Did I mention that I drive fast?

I made a little kit for a buddy of mine with a '13 Expedition.

 

[3tonsoffun]

So, I'm running LT275/60R20 Yokohama tires measuring 33.3". Factory fitment is around 32". I love the look, the LT construction and the minor lift. I don't like that the MPGs went from 16.5mpg to 14.5mpg. These tires are 10#s heavier, and of course, taller. So what caused the drop. Could be the weight, but I suspect air underneath the truck. Putting on our engineering cap and reading the interwebs, I confirmed how simple front airdam design works. So I didn't have any problem finding something I could add to the bottom to extend the factory one down.

I used this: Trim-Lok DD1201-25 EPDM Dual Durometer Rubber/Metal Carrier Flap Seal, Fits Edge 0.050" - 0.090", 0.925" Flap Length

This is made from a EDPM rubber. Super flexible. It can take a lick. Steel wire core.

You get 25' of it. It's expensive @ $64.20, so you might want to convince a few friends to give it a try with you. I used stainless #8 screws with painted black tops to secure them to the HDPE air dam. The seal goes on good and tight, but you need the screws to keep it on if you drag over something.

The results? 16.0mpg

I didn't get all of it back, but enough to make this worthwhile. Did I mention that I drive fast?

I made a little kit for a buddy of mine with a '13 Expedition.

Hate to tell you that adding 1/2” of rubber to an air dam isn’t going to get you 2mpg and your crazy if you think it is. Probably a difference in driving style and fuel quality for you to get that difference. For comparison, my 16 EL with 35s gets 18 and I removed my air dam completely so...

 

[3tonsoffun]

Oh and I’m running a 93 performance tune also so not too sure what’s going on with your set up

 

[mcloven]

or, maybe its because the gas stations should be changing over to summer blend gas and you will get better mpg with the summer blend and warmer temps. i usually get a full 1 mpg better over the winter blend

 

[07navi]

Not the air going under or the heavier tires but if you went to a more aggressive tread it's partly that and the larger diameter.
I do have a question; did it have a air dam originally? I just bought mine and there is none.

 

[Menard LaDouche]

Changing from 32 to 33.3 diameter is 4.1% different, quite close enough to your 5%. So keep in mind that 16.5 mpg with the old tires will read 15.8 mpg with the new tires. Same gas efficiency! Different odometer reading, by 4.1%. If you are now driving 14.5 mpg, it is because you are happy and accelerating with the new big tires. Try cruise control, you might just get it back (to 15.8).

 

[buffy]

God Bless everyone's opinion. I'm just collecting general data. I was at 16.5 before the tires. I was at 14.5 after the tires (for 2,000 miles). My driving habits are consistent. Tons of highway. I have a daily 60 mile commute. After the modification it went right back to 16.0. I've run it 4,000 miles like this. My decline in mileage was likely attributable to air getting under the vehicle and the added rotational mass of the tires. It was simple to experiment with the air getting under the vehicle. These are the results. Feel free to ignore it. There's a reason they put airdams on these things. Fluid dynamics are very counterintuitive on results at times and especially something as messy as the underside of a car. That's why engineers like to minimize the air getting underneath. It shouldn't shock anybody to see a surprising result there. Luckily, It doesn't take a rocket scientist to design efficient frontal airdams. It's air diverting structures at the back of vehicles that are hard to model. But if it makes you feel better, I have a decent degree in mechanical engineering. I'm not just stabbing in the dark.

 

[3tonsoffun]

God Bless everyone's opinion. I'm just collecting general data. I was at 16.5 before the tires. I was at 14.5 after the tires (for 2,000 miles). My driving habits are consistent. Tons of highway. I have a daily 60 mile commute. After the modification it went right back to 16.0. I've run it 4,000 miles like this. My decline in mileage was likely attributable to air getting under the vehicle and the added rotational mass of the tires. It was simple to experiment with the air getting under the vehicle. These are the results. Feel free to ignore it. There's a reason they put airdams on these things. Fluid dynamics are very counterintuitive on results at times and especially something as messy as the underside of a car. That's why engineers like to minimize the air getting underneath. It shouldn't shock anybody to see a surprising result there. Luckily, It doesn't take a rocket scientist to design efficient frontal airdams. It's air diverting structures at the back of vehicles that are hard to model. But if it makes you feel better, I have a decent degree in mechanical engineering. I'm not just stabbing in the dark.

Idc If your a mechanical engineer, a plastic air dam with 1/2” of rubber on it does not net you 2 mpg. Too many other variables go into mpg like air density, outside temp, wind speed and direction, fuel quality, driving habits, the list goes on. Stop spreading false info please

 

[joethefordguy]

Idc If your a mechanical engineer, a plastic air dam with 1/2” of rubber on it does not net you 2 mpg. Too many other variables go into mpg like air density, outside temp, wind speed and direction, fuel quality, driving habits, the list goes on. Stop spreading false info please

damn your experience, man! I know what I know! Don't confuse me with your real-world experience! Stop spreading false info about the real world!!!

 

[coupe11]

In college we had a very good professor. One so good that when the class schedules came out for the next semester you had to quickly run down to the sign up tables and sign up before his classes were full.

He had a plaque on his desk that read, "My mind is made up, so don't try to confuse me with the facts."

I always got a kick out of that, especially considering his knowledge and personality.

Airflow is a very misunderstood thing. Having spent 30 years in a couple of plants that used both fans and positive displacement blowers to convey material for up to several hundred yards into/out of rail cars, bunkers, trucks, bunkers of various sizes/locations I've seen some weird stuff and been told some real stinky BS by supposedly very knowledgeable experts who knew what they were doing/saying - right up to the time you showed them how the real world was treating their "beliefs." Sometimes it was funny to watch them get upset when the real world and their education, or computer models, didn't match up so well. Sometimes it was frustrating as hell to hear them keep repeating over and over that, "That can't happen." Even when they looked at it, they refused to believe it was happening.

I especially hated those somewhat routine inspections by FDA officials or EPA people. Seen some of them do some really stupid stuff that made me wonder what the injury rate is among government employees. I guess they figured that little badge/nametag made them immune from injury when they stuck their heads/hands some place they shouldn't.