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Fuel Economy on 2WD vs. 4WD

Posted by cheerful1 (My Page) on
Wed, May 4, 05 at 8:53

I was on the website www.fueleconomy.gov to compare mileage on my car and my truck. There's different mileage for my truck based on 2WD and 4WD. My truck can go either way. If I drive in good weather, and am just in 2WD, do I follow the fuel economy for 2WD?


Follow-Up Postings:

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RE: Fuel Economy on 2WD vs. 4WD

I think the fuel economy differences are for trucks without 4WD at all (2WD) and for trucks with 4WD.

I don't believe, under normal driving conditions, you are supposed to be using 4WD at all...and the EPA likely wouldn't have tested the truck with 4WD on.

So you'd get the fuel economy of a 4WD truck, even when it's in 2WD mode.


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RE: Fuel Economy on 2WD vs. 4WD

Right, if you have a 4WD truck, you have to use the published economy figures for the 4WD, not the 2WD, even if you're not using 4WD.

With a 4WD truck, the fuel economy is lower than the 2WD version for a lot of different reasons, even when the 4WD system is off. For instance, a lot of 4WDs sit up higher and are less aerodynamic as a result, they carry around a lot of extra weight that the 2WD vehicles don't have (transfer case, front half-shafts, etc.), and they may be geared lower to allow for better pulling and off-road use.


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RE: Fuel Economy on 2WD vs. 4WD

4 wheel drives have extra weight to haul around and a little more loss in the drive train. On my Jeep, I have an additional differential and axle assembly up front, a drive shaft running from the tansfer case to the front differential, two U-joints for the drive shaft, and 2 more U-joints for the front wheels, plus the transfer case itself. That's got to be 200 more pounds or more.

When in 2 wheel mode, its only the center differential (in the transfer case) that is disconnected, and the front differential is unloaded, but all these front drive parts are moving and there are some losses from these even when unloaded. This amounts to about 1 to 2 miles per gallon penality during trip driving. I have both modes, part time and full time. With full time mode engaged, the mileage penality is 2 miles per gallon or less.

Part time mode should not be used on paved or dry surfaces; It may be used only on surfaces where the wheels can slip relative to each other.


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