Which is the best gear to go with 4.11 or 4.56 with 37" tires?

[klandgraf]

I have a 2004. 5 Dodge Ram 2500 4X4 Cummins automatic with the 48RE and 3. 73 gears. I had 34. 5" tires and I was running 70 mph @ 1750 rpm empty and getting 18 mpg hand calculated. I recently put on 37 13. 50 20 Toyo mt's and now I am getting 12 mpg and running 1600 rpm at 70 mph. I do mostly highway driving of 70 mph and above with very limited towing. I bought this truck with the 34. 5" tires so I don't know what the stock tires and the higher rpm does for mileage. Does anyone know? According to the charts with the 4. 11 gears I would be @ 1800 rpm @ 70 mph and with the 4. 56 I would be @ 2000 rpm @ 70 mph. I have plenty of power for the tires and I have gps and the smarty for tire correction and speed. I like the lower rpm but I don't know if it's enough to get me close to what I was with the 34. 5" tires. Any suggestions would be greatly appreciated? Thanks

 

[Bob4x4]

The 4. 10s are good enough for hiway cruising but not so good for towing unless you have a very aero trailer like mine and don't do much mountain towing or are ok with towing out of od.
The 37" toyo's cost me some mileage from the 35's so swapping gears will not give you all the mileage back

 

[LNaugle]

I usually swap out to 4. 10s for most people, did do 4. 56s in a mega cab dually that had 37s and always had a welding machine in the back and he loved it.

 

[p-Bar]

The 4. 10s are good enough for hiway cruising but not so good for towing unless you have a very aero trailer like mine and don't do much mountain towing or are ok with towing out of od.
The 37" toyo's cost me some mileage from the 35's so swapping gears will not give you all the mileage back

So Bob I was thinking of going to 4:10's but it sounds like it may be a mistake pulling my 14k trailer?

 

[klandgraf]

I usually swap out to 4. 10s for most people, did do 4. 56s in a mega cab dually that had 37s and always had a welding machine in the back and he loved it.

Do you know what they are getting for mpg with the 4. 10 and 4. 56 gears with 37" tires on the highway not towing? What do you think should be the best highway rpm for mileage and not towing?

 

[klandgraf]

The 4. 10s are good enough for hiway cruising but not so good for towing unless you have a very aero trailer like mine and don't do much mountain towing or are ok with towing out of od.
The 37" toyo's cost me some mileage from the 35's so swapping gears will not give you all the mileage back

What setup are you running and what mileage are you seeing not towing? What highway rpm do you get the best mileage not towing? With my 3. 73 going 70 and running 1600 sounds like it's lugging alittle but it never downshifts and if I hit the pedal it takes right off, but I think it would be alot better if I could get the rpm's up to at least 1800 at 70 mph. Thanks

 

[AEdelheit]

I have 4. 10's and 355/75/18 Toyo A/T, equals a 37x14. The 4. 10 are good for daily driving and freeway by my truck doesn't tow that well. The biggest problem IMO is the 48RE ratio between 3rd and OD is way to much, when towing its very annoying. I use OD on the freeway and if the trailers about 5k or less. The nice thing about 3. 73 for towing was that In 3rd gear the rpm was good for towing on the highway, with 4. 10 it's a bit high and 4. 56 you would need OD.

 

[Bob4x4]

So Bob I was thinking of going to 4:10's but it sounds like it may be a mistake pulling my 14k trailer?

Not sure what size tire you are running,Bone stock engine and tires my 4. 10s were perfect for towing,first trip out with it was the Sierras and the notorious sherwin grade. The brand new stocker ate it up- I think I had enough to pull it at any speed I chose.

 

[Bob4x4]

What setup are you running and what mileage are you seeing not towing? What highway rpm do you get the best mileage not towing? With my 3. 73 going 70 and running 1600 sounds like it's lugging alittle but it never downshifts and if I hit the pedal it takes right off, but I think it would be alot better if I could get the rpm's up to at least 1800 at 70 mph. Thanks

To start I guess I should admit I have all the upgrade for added air short of a cam and no ported head yet,and I can vary the amount of fueling,
I prefer to tow at about 375 hp to the ground. It is a good compromise between power and not too hard on the drivetrain.
The 4. 10s and 35" tire combo works out to about the same rpm as a stock tire and 3. 73's
My trailer is only about 6k and being an airstream it does not push a lot of air. I get anywhere between 13 and 17mpg while towing depending on road speed and how many grades. I have tried 3 different turbos and so far none are ideal in all situations.
Like Aaron said the 4spd auto is less than ideal for having a good rpm for all driving situations. The 6 spd would be a huge upgrade for towing heavy.
I can hover around the 2o mpg neighborhood empty at 65-70 driving easy. Throw the 37's on and I loose about 1. 5-2mpg
Both my trucks like 17-1800rpm cruise rpm empty. Since I am usually towing with people that are not. My truck has to be more flexible to stay with the convoy

 

[TCDiesel]

If you want the correct sweet spot for mileage Just Speed/RPM are 2 out of 5 You need to know, the 5 are TPS or APPS,RPM,Engine Load,Boost,Grade. Speed is just a touch-tone and and most cases faster means more fuel consumption. Boost is the key factor higher the boost the more fuel consumed. Example you could be traveling @ 0 grade @ 70 MPH, with RPMs at 1800 with boost @ 8PSI = XX Mileage,Now the check it at 68 MPH the Boost will drop to 4PSI @ the engine load will drop 5/10% that will equal better mileage. Now when changing gear(s) (Axle) the RPM will increase and with most conditions the Boost will drop, In general More Boost =More Fuel, Higher RPMs adds More HP with less Boost,its finding the best combination to +/- Mileage, if You own The Banks IQ you can view Grade,Added Power,TPS or APPS,EGT,Boost,load ALL at once, Every Drop of Fuel is measured and account for on My personal trucks (Auxiliary tank) ,I travel form MN to the Rockies 3-4 times a year Pulling My 4 place Snowmobile Trailer ,the sweet spot for Mileage continely changes do to conditions, ALL My company and Personal Truck have 4:10s, the times I had 3:73 gears I did not like (I want to be Quick) NOT fast, I generally drive 65-70 MPH,the 4:10s will net better mileage for city driving, and if you tow 3:73 and 4 Speed AT just *****.

 

[Bob4x4]

Well said Todd

 

[LNaugle]

I agree with Todd... Also why my 96 has 4. 10s and a nv5600 swap. I'm able to pull Vail and Eisenhauer Pass (which are in the top10) running in the fast lane. Its all about your combination.

 

[HBarlow]

IMO 4. 10 gears (with stock tire/wheels) are the preferred and only gear choice for towing or performance. I learned that lesson with my first Dodge-Cummins. It was an '01 HO/six speed and I specified 3. 54 gears. The 3. 54 gear worked fine towing a relatively light 8,000 lb. Airstream and 8,500 lb. Avion. Later when I moved on to a 14,000 lb. fifthwheel the 3. 54 gears became a poor choice.

Since then I have specified only 4. 10 gears. 4. 10s work great with the 48RE because it has a tall overdrive and work even better with the new MOPAR or Aisin six speed automatics which have two overdrive ratios.

 

[Wingate]

im from the old school thought. . give me all the gear I can get. . I want pulling power!. If fuel mileage suffers, so be it... I HATE running out of truck!. Usually the mileage difference isnt significant enough that it cant be overcome by adjusting driving habits.