Question Optimum cruising RPM

[Joe Hogan]

The Cummins diesel engine in a 2024 DutchStar, K2 Chassis, it appears to be 1700-1750 rpm. The Coach runs with enough power to top most hills without loosing speed. Gets reasonable fuel economy and paces traffic well.
Able to avoid pacing trucks that are governed at 65 mph.

Seems overall a good choice for the Coach, Of coarse depending on road and conditions.

 

[Crazydog]

In my 2017 Ram Cummins powered pickup it seems to like 1900 rpm which in 5th gear is good for 65mph. That is also my self imposed speed limit when towing a trailer.
It take smost highway climbs without needing to downshift at all.

 

[RVThereYet]

My 2022 F250 Diesel seems at 1700 RPM in 10th gear and 65MPH is very comfortable. Depending on hills, wind, it normally gets 10-12MPG pulling our 5er. I'm very happy with that!

 

[MemoriesByTheMile]

In our 2014 Renegade with the Cummins ISX600/15 coupled with the 6 speed Allison, RPMs right around 1350-1400 seems to be the sweet spot for torque and fuel economy. This RPM with our Allison 6 speed results in a cruising speed of roughly 64-66.
It actually gets better fuel economy at this speed/RPM than it does if we travel at 60mph. At 60 mph there is much more lugging and slow down on the hills.

 

[sheridany]

What I have learned, either with Newmar or Prevost, is that the sweet spot is 14-18 on flat or slight hills, and the higher you run your rpm, not exceeding 2100 (on a Prevost), the cooler it actually runs because the fans kick on, etc. You will see the temp gauge drop as you downshift to push up the RPM's higher.