I've read the MPG thread but couldn't find exactly what I am looking for.
Can anyone give me any real world input on what difference in MPG you will get with 3.92 instead 3.55? Terrrain in my area is slightly hilly.

Thanks

 

Probably get a tad better with 3.92s.Takes less horsepower to move the vehicle.I get 20mpg at 70 to 72 mph.What I call in town never less then 14 to 15.

 

Just my 2 cents, and please understand I'm not picking at you at all.

It'd be really tough to get the information you're looking for. To get an accurate picture of the mileage difference between a truck with 3.55 gears and another with 3.92 gears, you'd have to run them back to back on the same routes, same speeds, same driver and filled up at the same place. Anything short of that is going to be pure guesswork. Everyone drives a little different. Some have 20 inch wheels, some 17's. Some have regular cabs, some have quad cabs, some have crew cabs. Some people carry stuff all the time, some don't. Some have tires with lower rolling resistance. Some run 87 octane, some 89 octane, some run the 10-15% ethanol blend, some don't. Some are in cold weather, some aren't. All I'm trying to say is that there are a truckload of variables that are going to affect the fuel economy just as much or more than the gearing. Dodge doesn't seem to differentiate between axle ratios on the fuel economy ratings on the window sticker...just whether or not the truck is 2X4 or 4X4 and which engine it has. That's likely because the differences are pretty small.

In theory the 3.55 gears should net slightly better fuel economy than 3.92 gears. Three key words in that sentence: theory, should and slightly. It's roughly a 200 rpm difference at the same highway speeds...not much at all. But more than likely, the best 1500 on gas would be a regular cab 2WD with 3.21 gears and 17 inch wheels, the worst would likely be a crew cab 4X4 with 20 inch wheels and 3.92 gears.

My thoughts: If it's at all possible, I try to get the lowest gearing available (highest numerically). The truck will feel snappier and be rated to tow more. But that's just me. I don't worry about the fuel economy in my truck...my VW TDI is the car I drive for good fuel economy. For you, go drive a truck you like with 3.55 gears, and drive another with 3.92 gears. Buy the one you like more and be happy.

 

I've had two Rams. One with the 3.92 and one with the 3.55. 3.55 can get you better mileage on the highway because you're not turning as many RPMs. 3.92 can get you better MPG driving in the city and I believe in the hills because it would take less to move the truck up the hill. Personally, I'm happy with the 3.55 I have now because I do more highway driving and I never tow more than 6000 pounds.

 

Do a "3.92" search on this forum and you will discover that some owners have swapped out 3.21's and 3.55's for 3.92's. If a poll were taken, the 3.92 would win hands down for both performance and economy.

I live in a "hilly" area and wish I had opted for the 3.92.