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Downspeeding and Gearing for Fuel Economy with the 2013 ISX15

Gearing recommendations are changing for the 2013 ISX15, to provide better fuel economy for your customers while maintaining safe and driver-pleasing performance. This process, called downspeeding, will enable trucks to run 65 mph at a lower rpm, and may result in additional fuel-economy savings.

Maximum fuel economy will be achieved with 2013 ISX15 engines with ratings from 400 hp to 450 hp (298-336 kW). Vehicles running fully loaded with 80,000 GVW at 65 mph should be geared in the range of 1260 rpm to 1280 rpm. This gearing works best for trucks that spend a high percentage of time in top gear in interstate highway operation.

For a general fleet spec with operations running regional routes in mixed driving conditions, including both highways and two-lane roads, Cummins recommends that 2013 ISX15 engines from 400 hp to 450 hp (298-336 kW) be geared at 1370 rpm to 1400 rpm.

For fuel-conscious fleets that spec engines from 475 hp to 600 hp (354-447 kW), 1400 rpm to 1435 rpm is ideal.

Be sure to visit to get the latest gearing recommendations and electronic parameter settings for Cummins engines. As always, consult your Cummins distributor for assistance with gearing your ISX15-powered truck.

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