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Old 09-19-2021, 10:04 AM   #1
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Dumb Question 4wd vs 2wd MPG

I have been going back and forth for years between a 4wd conversion or leaving my van 2wd. One consideration has been MPG because I assumed I would loose a lot with 4wd. Wondering now if most of the loss would just be the tire size increase?

Looking at using a MG kit (which I currently have) or going with a Weldtec 5” 2WD kit. Would use a 33” tire with the MG kit or 32 or 33” with the Weldtec kit. The MG set up would have 4.30 gear ratio and Weldtec would have 4.10 or 4.56.

What kind of mileage differences do you think there would be? Obviously the front axle would add some weight and reduce it a bit but would it be drastic?

For reference, it is a 04 5.4lL e350 30” street tire.Currently averaging a corrected 13.5 MPG over the last 5k miles of mixed driving.
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Old 09-19-2021, 10:18 AM   #2
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The two primary factors for MPG reductions are:

-Increased drag caused by higher ride-height
-effective gearing from taller tires changes which can put overdrive below the the power curve, requiring frequent downshifting. Or conversely, putting in too low of gears (numerically higher) causing your engine to spin faster than it needs to when cruising.

The difference between the same lift 2wd and 4wd is negligible.

Unrelated to lift and drive-train…. Those fancy racks have an MPG impact too. Especially the ones with front overhangs and giant light arrays at the top of the windshield.

Anyways…. Most 4x4s average about 10. You might a little better being 5.4L.
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Old 09-19-2021, 10:21 AM   #3
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Oh, and don’t forget about cruising speed. If I keep it to 60 MPH I average 9.5 MPG pulling my 38’ 13,000 pound trailer. That’s barely worse than non towing except when I don’t have the trailer I’m usually going quite a bit faster.
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Old 09-19-2021, 10:23 AM   #4
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2008 5.4L 4WD 3.73 gearing 285/70-17s gets 11-12 mpg depending on speed.
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Old 09-19-2021, 10:26 AM   #5
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Thank you for that! Very much along the lines of what I was thinking.

School has given me a recent kick for spread sheets. Running through numbers of 4wd vs fancy 2wd kit has made me realize that they are not miles apart in price, especially considering I already have the MG Kit, transfer case, and a lead on some nice 4.30 axles with an e-locker. Both axles are cheaper than regearing and adding an ARB to my current 2wd axle.

Fuel mileage was one of the question marks renaming. Thank you for the reply and info!

Joe
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Old 09-19-2021, 10:30 AM   #6
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Originally Posted by boywonder View Post
2008 5.4L 4WD 3.73 gearing 285/70-17s gets 11-12 mpg depending on speed.
That’s interesting! Never thought I could get away with 3.73’s and 33” tires with the 5.4! I also have a set of 2014 axles for the conversion but they are open diff 3.73s so I never even considered them (everything for 4wd was bought together in one big package).

Still think I would enjoy lower gearing but glad to hear this is a possibility! Thanks!
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Old 09-19-2021, 10:35 AM   #7
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That’s interesting! Never thought I could get away with 3.73’s and 33” tires with the 5.4! I also have a set of 2014 axles for the conversion but they are open diff 3.73s so I never even considered them (everything for 4wd was bought together in one big package).

Still think I would enjoy lower gearing but glad to hear this is a possibility! Thanks!

It struggles on grades....I'm presently re-gearing to 4.10s. Front is Done, need to do rear.
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Old 09-19-2021, 10:43 AM   #8
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Ah gotcha. That’s why I wasn’t even going to mess with these current 3.73 axles and try to sell them to someone with a diesel. I don’t trust myself to do a regear and shops charge an arm and a leg to do it around here. Was a lot cheaper for me to go with factory 4.30 axles if going 4wd.
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Old 09-19-2021, 12:58 PM   #9
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If you're doing a $ comparison.... you'll get your money back on 4x4 and then some if you ever sell. Not the case with a 2WD lift. In some areas, it might even sell for less than a stock 2WD, because it's not any more capable in mud and snow, but it can imply some hard dessert-driving may have happened.
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Old 09-19-2021, 01:58 PM   #10
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If you're doing a $ comparison.... you'll get your money back and then some if you ever sell. Not the case with a 2WD lift. In some areas, it might even sell for less than a stock 2WD, because it's not any more capable in mud and snow, but it can imply some hard dessert-driving may have happened.
That was the biggest “aha” I recently came too. Return on investment would be a lot higher with 4wd. I am such a hard core cheap butt that I often have trouble remembering that spending a little more now may equal much more in the future.

Thank you very much for reinforcing that!
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