Selecting the right rear ratio

campfire7

Active Member
I Am looking at a 2015 F250 gasser 4x4 to pull my 30Ft. North Country TT, ( less than 10.000 lbs) But I am not sure which gear ratio to chose. One that will work well and provide the best fuel mileage. Any suggestions will be appreciated.

Non limited slip or Elect. locking

3.73 / 331 / 3.55 / 3.75 / 4.30
 

jnbhobe

Well-known member
I would go with the locker and 3.73 gears or 4.30's. I am pricing a F-350 DRW with 4.30's now.
 

JohnD

Moved on to the next thing...
The best gear ratio for towing and the best gas mileage don't necessarily go together.

The 4.30 will be the best for towing, but not the best for mileage.

However, if you are going to stick to the flat lands, then perhaps the 4.30 would be overkill.

We pull in the mountains, which is why I chose the 4.10 rear end in my new Chevy 2500HD . . . glad I did!
 

NWILSON

Kentucky Chapter Leaders - retired
There's a couple trains of thought here. Check the towing/loading charts and go with the best ratio (smallest number) that will keep you within the load limits for your truck/trailer combination. In theory this will give you the best mileage.

On the other hand if there is any remote chance that you'll be upgrading rigs you might want to go with a higher ratio to allow you to pull a heavier rig without having to buy another truck.

Not an easy decision!
 

Gaffer

Well-known member
Think about where your peak torque is at in RPMs in tow haul mode if you have one (not in overdrive) at towing speed. You may find that 3.73 will work for you. Take into consideration how often you will encounter 6% or greater grades.
 

Bob&Patty

Founders of SoCal Chapter
I would not go any higher than 3:73's. 4:10's might work...4:30's would be fine except for a high revving engine a highway speeds. 3:50 or 3:23's would be a power killer.
 

Bohemian

Well-known member
You also need to know the transmission ratios. Ram offers two different transmissions for the diesel trucks with differing transmission rations and thus different drive ratios. The 3.42 with one transmission has about the same 1st gear drive ration as the 4.10 with the other transmission. The 4th and 6th gears in both transmissions are the same. Thus the lower gear ration diff will be expected to get better fuel economy on the highway in 4th, 5th or 6th gear.

With Ford and GM you get no transmission choice, so pick which you want more. Fuel economy, or tow capacity.

When it comes to payload, the diff makes little difference. It's mostly about tow capacity.
 

JohnD

Moved on to the next thing...
I Am looking at a 2015 F250 gasser 4x4 to pull my 30Ft. North Country TT, ( less than 10.000 lbs) But I am not sure which gear ratio to chose. One that will work well and provide the best fuel mileage. Any suggestions will be appreciated.

Non limited slip or Elect. locking

3.73 / 331 / 3.55 / 3.75 / 4.30

So . . . what did you get?
 

fredwrichardson

Past New Mexico Chapter Leader
I Am looking at a 2015 F250 gasser 4x4 to pull my 30Ft. North Country TT, ( less than 10.000 lbs) But I am not sure which gear ratio to chose. One that will work well and provide the best fuel mileage. Any suggestions will be appreciated.

Non limited slip or Elect. locking

3.73 / 331 / 3.55 / 3.75 / 4.30

A gas truck that is a V8 is going to produce most of it's torque at a much higher RPM than a diesel. The fact you are choosing a gas engine means you will have to go to a higher gear ratio. I would do no less than 3.75 but if you want to be able to pull in the mountains then 4.3 is going to make more sense. If you are looking at Fords make sure you look at the eco-boost V6. It actually pulls more torque at a lower RPM than the V8. If you are looking at RAM then I would jump all over their new EcoDiesel. That engine has great MPG but also has the torque to easily pull your trailer.
 
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