Well I don't mean to be flippant, but isn't that almost immaterial?
While there is probably a slight difference between the two, it would be due to some extra weight and a slightly higher drag caused by the fact that the front end is not completely free turning as a 2wd would be. Possibly your mileage concerns might be based on some vehicles with full time 4wd versus 2wd, that would be more of a difference. The initial attempts at simplifying the 4wd concept produced some trucks where the front end was not free turning at all in order to simplify the operation of the system.
That's not the case with the new GM diesel trucks. There is another thread on mileage of the Duramax trucks, which I spotted thanks to another post I just saw, that might answer your questions:
I like to compare 4wd to air conditioning. Being old enough to remember when most cars did not have it, once you bought a vehicle with air conditioning, you'd never buy one with out it again. For me, it's been over thirty years since I've bought a vehicle that did not have 4wd.....
A guy I work with has a truck like mine - same year, cab/bed and options except color, he's got rear window defroster and his is 4wd versus my 2wd. We've checked our empty mileages, and there seems to be a 1 mpg or less advantage to my truck. We haven't been able to fairly compare towing, since I pull a 5 ton fifth wheel and he pulls a 3 ton travel trailer or a 2 ton utility trailer. Edited by: bluenote
I know that this has been discussed before and I don't think there is a huge difference between the two. Most importantly is how you will use the truck if you think you might want the 4WD I would defininetly get it. IMHO Why get the truck you want and not get a very useful function? I know that several people that tow trailers have been glad they had 4WD in some slippery conditions w/trailer. I think that the biggest diff in milage is automatic vs. manual trans. No matter what you decide these are fantastic trucks. Good luck with your decision.
If you change trucks fairly often, you may want to get a 4wd simply for resale value. I tend to latch onto a vehicle and drive it for a long time, so this is not an issue for me, but I also refuse to ever buy another vehicle that I can't have both ends pulling if I want.(2-wheeled vehicles are the only exception to this!
) I do know that 4wd makes a vehicle easier to sell/trade and worth more when that time comes.
My impression from reading this and other sites is that the inherent mileage difference between two and four wheel drive is probably less than the differences resulting form production variability among trucks of the same configuration.
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