Specs for otr flatbed

OD 13 or direct? 3.70-3.90 depending on target speed with OD, 2.70-2.90 ish direct also depending

 

Depends on what the 13 speed is.
You have to look at what the combined ratios for the transmission and the differential are. Have run 3:70, 3:55 and 3:42 diffs with a 13 speed transmission. All had slightly different characteristics.

 

Good points. Expected terrain also changes the equation

 

In my opinion 3.73 or 3.90 if your planning to load heavy(above 85K) to off pavement points (construction sites etc) or mountainous terrain.
Between 3.55 and 3.08 if limited off pavement type work or light loads.

 

All a 13 speed is, is a 9 speed overdrive transmission that can split the top gears. Basically overdrive on or off.