The 3.43 Rear end

AlaskanHillBilly wrote:
I have a 07 Dodge and have a 3.73 rear end. I am thinking of trading it for a 2013/14 and have been told that I would get better gas mileage with the 3.43 rear end. I am towing a 14,000 lb 5th wheel. Does anyone know if that is true.

Hey there. I did a bit of research on this topic as well. Here is my opinion:

Given that the torque curve of the new 850 ft-lb Cummins is not flat anymore, and that it peaks out at 1700 rpm rather than 1500 rpm like previous engines, it seems strange to me to have a 3.42 axle ratio. On the other hand, having 4.10 axle ratio, putting the engine way above peak torque, would not be wise either. With the new Cummins/Aisin combination 3.73 would be the best match by far in my opinion. For 2013 you can only get 3.73s in a dually, not sure about 2014s though. (I should note that IF my truck was going to be a daily driver/commuter and would only pull hard a few times a year I might try 3.42s anyway, even if they weren't the best combo for towing)

Peak torque of 850 Cummins = 1700 rpm
RPM at 70mph with 3.73 = 1750 rpm
RPM at 70mph with 3.42 = 1590 rpm