I know that MPG is in the sticky but alot of people didnt put the rearend gear ratio. My truck is a 4.7 QCSB w/ 3.55 gears w/ 33" tires. I am considering doing 4.10 gears just not sure how this will effect gas mileage. Also does anyone know how to tell if the truck has the tow package?? It has factory hitch just sure. Thanks any and all help is appreciated.

 

i just bought a r&p from randys r&p my truck has the 3.90 and i am going to the 4.56 i have no power it will be in tue. so if you wait a week or so then i can tell you how it go's.
i have a 05 dodge ram quad cab 4x4 4.7 with 305 tires my gas milage sucks but i cant even pull my truck down the road with out it going in and out of overdrive and that was before i got the bigger tires.

 

3.92 to 4.56 gear swap got meabout 1.5 mpg better around town, about the same on around town highways (45-55mph), about 1mpg less when cruising 60-70mph down to about 2 mpg less when cruise controlling at 85 on the Interstates.
and a whole lot more pull with 35" tires!

 

I have the 4.7, 4WD, Quad Cab and all bone stock, except for these upgrades:

Extra Transmission Cooler with Fan
Transmission Temp. Gauge (in a pillar pod)
Fog Lights (added the factory setup just this week)
4.56 gears (upgraded from 3.55s about 8 months ago)

The difference between my stock gearing and the 4.56s is well worth the money it cost to do both axles. I pull a travel trailer (about 4000# loaded) and have seen an increase in towingmileage of about 2 MPG. Towing, I used to get 10 MPG. I am now getting a fairly solid 12 MPG under the same towing conditions.

Around town, I got about 10.5 before the gear change. I am now getting 11.8 long term average - a little over 1 MPG.

Running empty on the highway, I was struggling to get 15.5 while doing an average of 65-70. Now I am getting around 17.5 - another 2 MPG gain. I have not run sustained speeds above about 70 (the max. in our state.

So overall I have gained MPG in every category.

Remember that this is with the 4.7 liter engine. This engine does not have a lot of torque and I personally think that it is underpowered for the size and weight of the truck - at least with the stock gearing. Lowering the gears increases torque at the rear wheels by the factor of gear reduction (if you are interested in the math, let me know and I'll run through it for you). Going to a 4.56 gear took quite a load off of the engine, saving wear and tear - and gas - especially when towing.

I don't know if the mileage figures would be the same for the Hemi. I seriously doubt it however. The Hemi has a lot of torque and HP to begin with, so no need to compensate with gears. I used to have an '01 with the V-10 and 3.55 gears. Great setup, but that engine put out a peak 450 lb.ft. of torque at a fairly low RPM. Going to a shorter gear in that truck would have been a disaster! That may be true with the Hemi - I don't know. Someone else may be able to chip in here that has changed gears in their Hemi.

 

Well I have a stock 06 MDS Ram with 40k. Right now i get a pretty constant 18 mpg(calculated not computer)on the Highway, but sucks around town like 11 to 13 mpg..
thinking on leveling the front, and changing to 33" tires. any ideas on what kinda mpg loss i should expect to see.

 

I'm glad there is a lot of talk about gearing because I am thinking about upgrading my gears, especially since most of my driving is city and not highway.

 

To avoid confusion
it is always a good thing
to stop talking about differential gear ratios
and tire diameters
and instead work out
how many MPH your vehicle is running for each thousand RPM.

For example, if your tach shows 2000 rpm at 70 mph
your drivetrain is 70 mph divided by 2 = 35 MPG/1000 rpm

In city driving MPG is almost entirely linked to how fast you try to make the truck accelerate...especially if you press the accelerator pedal past 80% down and get into the very wasteful 'fuel enrichment' part of the vehicle's computer programming.

There can be a 'psych' part to city driving.
If your truck is very noisy and if you are hearing a lot of 'gear whine' you might unconciously drive a bit slower. This is because most people drive partly by ear.
The reverse can also be true.
Ever driven a friend's very quiet luxury car for the first time...and suddenly found yourself way over the speed limit when you look down at the dashboard?

For highway driving at 60 mph to 80 mph
with a "lightly loaded" truck
the best drivetrain for a V8 or V10 gasoline engine pickup
is at least 37 mph/1000 rpm
and the MPG will get better up to 45 mph/1000 rpm
{but the truck will downshift to pass or to climb hills}

But if the tires chosen are 'high rolling resistance'
you will get poor MPG despite the drivetrain or speed.
Blocky mud style 'sticky' tread on tires are almost always hard to roll.

As you put a load on a pickup either with
weight in the cargo box
or towing a trailer
or climbing long hills,
the MPG is always going to go down as horsepower used is increased,
but the
'best of the worst'
fuel economy in these loaded situations
is when the engine has a powertrain mph/1000 rpm
that allows it to run with a vacuum in the 7-10 range.
This is the same as having a MAP in the 22 to 25 range.

Small displacement engines (like having a 4.7 instead of a 5.7)
or engine with shorter crankshaft strokes (like Chevy 5.3)
need slightly higher
MPH per 1000 rpm drivetran set ups.

Sound complicated?

Rather look at a picture that explains this?

Look on page 336
of the Bosch Automotive Handbook
which you can read for free from your local library loan
or online at Google books if you have a gmail account: