Engine/Transmission (1998.5 - 2002) Cummins PowerSpec Software

[RobertMiller1]

In calculating the ideal gearing, it comes up as 4. 56 with stock (265x75-16) tire diameters.

Wasn't expecting that. with 70mph as cruise speed, where Cummins specifies 2150 rpm as ideal for efficiency in this engine.



Heck, I am now running 285x75x16 tires. I was contemplating changing to 4. 10's but was surprised by the 4. 56 recommendation.

 

[McDowra]

interesting, with stock tire size and 4. 56 gears i don't think a truck would have enough rpms to run much over 70.