N14 PLUS GEARING RECOMMENDATIONS

On-Highway 80,000 lb GCW Applications:

The gearing recommendations for an N14 Plus engine hauling up to 80,000 lb GCW are:

1. For maximum fuel economy (mpg): Select a gearing combination (transmission ratio, tire revs/mile, drive axle ratio) that will result in approximately 1450 rpm at a 65-mph checkpoint.
2. For vehicles that will operate at or above 65 mph: Select a gearing combination (transmission ratio, tire revs/mile, drive axle ratio) that will result in approximately 1450 rpm at a 65-mph checkpoint.
3. For vehicles that will operate below 65 mph and maximum fuel economy is not required: Select a gearing combination (transmission ratio, tire revs/mile, drive axle ratio) that will result in approximately 1550 rpm at a 65-mph checkpoint.

The formula for determining engine speed (rpm) at the 65-mph checkpoint for a selected gearing combination is:

It is important to utilize actual ratio and tire rev/mile information in selecting gearing combinations. A qualified truck salesman or a Cummins distributor can provide information on available transmission top-gear and drive axle ratios in addition to the actual tire revolutions per mile for a specific tire to be used on the drive axle.

Note: Lower numeric (faster) axle ratios are sometimes considered to obtain higher maximum vehicle speeds and lower engine rpm at the vehicle's normal cruise speed. When considering these combinations, one should be aware that: (a) the increase in maximum vehicle speed will be minimal, (b) the fuel economy benefit associated with lower cruise rpms is difficult to measure, and (c) most important, vehicle grade-climbing capability will be adversely affected resulting in increased gear shifts. To understand the relative differences among various gearing combinations, one should consult an authorized Cummins representative and request a Vehicle Mission Simulation™! (VMS).

Heavy-Haul Applications (greater than 80,000 lb GCW):

Performance of heavy-haul vehicles is application dependent. When selecting gearing for an N14 Plus engine hauling over 80,000 lb GCW, one should consult an authorized Cummins representative.