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Ideal Gearing — Performance or Fuel Economy?

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April 30, 2014 by Minuteman Trucks

When looking at geared engine speed, it is important to understand your preference for performance and fuel economy. A higher numeric rear end ratio achieves better low end performance. Conversely, a lower numeric gear end ratio decreases engine speed at cruise and provides better fuel economy. Rules of thumb within the industry are:

  • Heavy Duty: every 50 RPM = 1% fuel economy
  • Medium: every 100 RPM = 1% fuel economy

 

Four key attributes determine the engine speed at cruise and may be adjusted to optimize performance and fuel efficiency:

  1. Top Gear Cruising Speed
  2. Transmission Top Gear Ratio
  3. Rear Axle Ratio
  4. Tire Size (revs/mile)

 

The engine speed at top gear cruising speed is critical to fuel economy. Best practice is to gear for fuel economy at top gear cruising speed and adjust the axle ratio numerically upwards to meet the performance requirements. International® has developed the following recommended engine speed ranges, by engine type and application, for typical vehicle cruise speeds:

INTERNATIONAL RECOMMENDED ENGINE CRUISE SPEEDS

GearedEngineWhitePaper_InternationalRecommendedEngineCruiseSpeeds

See table below for examples of how to fine-tune engine cruising speed:

GearedEngineWhitePaper_HowToFineTuneEngineCrusingSpeed

Work with one of our Sales Representative to assist in determining the ideal gearing and engine speed for your application.

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