Why does 4 wheel drive affect MPG?

The simple answer is weight, all the extra components, axle, transfer case and driveshafts add up, plus larger tires and usually lower gearing to make the 4wd pull harder effect mileage even when a 4 wheel drive system is dissengaged. Now a full time 4 wheel drive system keeps both front and rear axle locked in all the time causing drag. Even most modern all wheel drive systems with computer controls and clutches and actuators to control the system still can't match the mileage a 2wd can accomplish.

this is true. here's why.

1. a 4wd vehicle weighs more. typically 3-500 lbs b/c of the added gears, axles and housings required. weight = fuel economy.

2. a 4wd vehicle has more friction. you are pushing the gears around, they have more friction than just the set of bearings that would be in those wheels otherwise.

weight and friction combined mean lower fuel economy. if the 4wd is turned on, there is even more friction which is why you get lower fuel economy with it on than off.

AWD means all the wheels have power all the time. 4 wd means that two wheels have power and two can be turned on by the operator if you need them.

It is true. all wheel drive adds components which weigh more than zero and it causes friction greater than zero.

There is not a technical difference between 4wd and awd. Rather, it's an advertising difference. If the system is fully automatic and has no low range, the advertising guys will usually call it "all wheel drive".

4 wheel drive lowers fuel economy because the engine has to turn all 4 wheels, this creates more drag.

if you have a vehicle that can select 2 wheel drive and 4 wheel drive, you will get better economy if you select 2 wheel drive.

all wheel drive is permamently in 4 wheel drive.

but with 4 wheel drive, you can select either 2 wheel drive or 4 wheel drive.

because Four wheel drive is more drag on the engine and its also more friction to over come.

4wd vehicles are carrying more weight than 2wd vehicles.

sophisticated factor. do a search into the search engines. that may help!

Weight and drag - it's not rocket science...

It probably used more power, and using up more gas