What's gears are best for pulling

It's not as simple as that,first we need know what type of freight you are going to haul and what region you plan on running IE: upper/lower east coast,mid west,upper/lower west coast?
It all depends on weather you will pulling light or heavy loads down flat or hilly terrain...

 

What size tires, what transmission, what is the max rpm of the engine, are you going to run on mostly 55 MPH roads?

This will determine what will work the best.

If you are thinking about the Freightliner with the 425 Cat, then the truck probably has 11R24.5 tires, a 15 speed direct transmission, and the engine will turn 2100-2200, as that is what it is designed to do.

With the 3.90 rears and the above specs, the truck will run 68 MPH at 2100. With 4.33s the top speed will be 61 MPH at 2100. 4.11s will put you at 65 MPH.

With a deep reduction 15 spd the 3.90 will do fine.

 

There used to be a graph on Eaton Fullers web page where you could type in your tire size, transmission, and differential gears and it would display a graph that would would tell excactly what your rpms would be for a given speed and gear. If you look around on thier website you might be able to find it, it's a pretty neat thing to play around with.

 

Try this:

http://www.roadranger.com/ecm/groups/public/@pub/@eaton/@roadranger/documents/content/ct_062746.swf


I just did the calculations on another site and it says that 3.90s will be around 70.5 MPH with 11R24.5 tires.

I like 4.11, but they have always had a drawback. With an engine that has an operating range of 1700-2100, which the engine your looking at has, if you are in a 55 MPH zone the engine is running wide open in 9th gear, and lugging to death in 10th.

I have owned and driven several 4.11 geared trucks. In the 55 MPH days I got more tickets in trucks geared 4.11 by trying to keep the rpms up so as to not be constantly changing gears.

At least with the 3.90 you can run in 9th in a 55 and not overspeed the engine so much.