Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - 4x4 mech drag - transfer cases (esp double), manual vs auto hubs, axles, etc.

stillsearching · 08-24-2014, 11:53 AM

Does anyone have any kind of specific figures for the amount of mechanical drag added by a 4x4 system? For those of us that need 4x4 ability i'm curious how to minimize the drag as close to 2wd levels as possible/I don't understand why there should have to be a 10% or more MPG difference...

For instance i've heard that 100% manual hubs on the front are worth about a 1/2 mpg difference. (some have claimed 1mpg but I don't think i've seen any documentation, yet even 1/2mpg adds up especially on a lower mpg vehicle) Apparently because even with the transfer case disconnected the front axle still freewheels and such causing drag. I would be very curious if this is still the case with modern trucks with the endless chase for MPG out there - whether this has improved and if something like swapping on modern hubs to an older pickup would maintain auto hub functionality, or if even modern ones have an MPG penalty for convenience.

I've heard that solid axle front suspensions exhibit worse mpg than independant ones due to the unsprung weight. I'm not sure why this is, increased drag on the front tires over bumps I could understand but highway should be pretty smooth normally?

The transfer cases themselves and range boxes i'm curious how much drag they add. Especially for things like doubler transfer cases if they make a big difference or not. (as I was hoping to look at steeper axles like 3.07's minimum or 2-something if I could get it made, then use a double rangebox to make it more driveable at other times... but if it adds alot of drag it may not work as well) Or certain models vs other models.

I know different axles have different amounts of drag, although I rarely see specific figures, outside of a Ford 9 inch is often the worst and anything by Dana usually the best due to something involving pinion position.

I've no clue how much would be eaten by different driveshaft or U-joint options. :)

I'm trying to figure out how much % of the total drag comes from different parts, seeking to optimize or change things around, and how to minimize the total system drag added by 4wd at all if I can. Maybe the ultimate answer is just adding FWD electric motors for on demand traction though. :)

08-24-2014, 11:53 AM	#1 (permalink)
stillsearching EcoModding Apprentice Join Date: Dec 2011 Location: Minnesota Posts: 201 Thanks: 45 Thanked 8 Times in 7 Posts	4x4 mech drag - transfer cases (esp double), manual vs auto hubs, axles, etc. Does anyone have any kind of specific figures for the amount of mechanical drag added by a 4x4 system? For those of us that need 4x4 ability i'm curious how to minimize the drag as close to 2wd levels as possible/I don't understand why there should have to be a 10% or more MPG difference... For instance i've heard that 100% manual hubs on the front are worth about a 1/2 mpg difference. (some have claimed 1mpg but I don't think i've seen any documentation, yet even 1/2mpg adds up especially on a lower mpg vehicle) Apparently because even with the transfer case disconnected the front axle still freewheels and such causing drag. I would be very curious if this is still the case with modern trucks with the endless chase for MPG out there - whether this has improved and if something like swapping on modern hubs to an older pickup would maintain auto hub functionality, or if even modern ones have an MPG penalty for convenience. I've heard that solid axle front suspensions exhibit worse mpg than independant ones due to the unsprung weight. I'm not sure why this is, increased drag on the front tires over bumps I could understand but highway should be pretty smooth normally? The transfer cases themselves and range boxes i'm curious how much drag they add. Especially for things like doubler transfer cases if they make a big difference or not. (as I was hoping to look at steeper axles like 3.07's minimum or 2-something if I could get it made, then use a double rangebox to make it more driveable at other times... but if it adds alot of drag it may not work as well) Or certain models vs other models. I know different axles have different amounts of drag, although I rarely see specific figures, outside of a Ford 9 inch is often the worst and anything by Dana usually the best due to something involving pinion position. I've no clue how much would be eaten by different driveshaft or U-joint options. :) I'm trying to figure out how much % of the total drag comes from different parts, seeking to optimize or change things around, and how to minimize the total system drag added by 4wd at all if I can. Maybe the ultimate answer is just adding FWD electric motors for on demand traction though. :)