Fuel Economy: 2wd vs. 4wd/awd

[82ColEd]

Someone please help me to understand this one:

I keep reading that AWD is worse for the fuel economy then 2WD. I am scratching my head on this one, as i cant figure out how that could be. The engine still has to move all 4 wheels, whether powered or not. I ran a comparison on the car i have that has the AWD (The Magnum) and the fuel economy is almost the same:

(From http://www-5.dodge.com/vehsuite/VehicleCompare.jsp)

R/T RWD
City: 17
Highway: 25

R/T AWD
City: 17
Highway: 24


(I picked the RT RWD vs the RT AWD to make it similar). So the AWD is 1 mpg off on highway mileage.. I keep reading magazines that are decrying the use of AWD if it's not needed (IE. dry roads, in the city etc).

So engineers, riddle me this: Are those magazines just blowing hot air or do they have a point ?


TIA!

-Stefan

[JohnZ]

The AWD system on the Magnum (and on the 300 and Charger) supplies 38% of engine torque to the front wheels at all times (and 62% to the rear); the 1-mpg reduction in highway fuel economy vs. RWD-only is probably related to a) The added weight of the AWD system (transfer case, differential, and axle shafts) and b) The parasitic/friction losses involved in turning all that AWD stuff full-time.

[82ColEd]

Thanks John,
that makes sense.. But then, with that said, there shouldnt be any case where it's really about fuel efficiency. Or are they just going after that 1mpg? Sorry, cant a link document to this, as it's in german.

Just baffles me how someone can say that AWD is ruiing the fuel efficiency of a vehicle.

[JohnZ]

Thanks John,
that makes sense.. But then, with that said, there shouldnt be any case where it's really about fuel efficiency. Or are they just going after that 1mpg? Sorry, cant a link document to this, as it's in german.

Just baffles me how someone can say that AWD is ruiing the fuel efficiency of a vehicle.

I wouldn't say it RUINS it, but it does reduce it slightly. However, if you look at it in a German context, they're paying about $6.00 - $7.00 a gallon, and fuel economy is a much more important consideration for them than it is for us.