Getting the best fuel economy is easy.
Use the road speed calculator below and start by entering your desired engine RPM at cruising speed.
Todays class 8 truck engines have an RPM "Sweet Spot" between 1450rpm and 1550rpm. The best fuel mileage will be seen in this range.
Truck manufacturer's will tell you it's between 1250rpm and 1500rpm but this is not true. If you run your truck at 1350rpm during cruise, you will lose approx. 10% of your potential fuel mileage.
After selecting optimum engine RPM, select tire size and finally transmission ratio, hit the calculate button and choose your Cruising speed and select the proper rear-end gearing ratio to run at the given speed.
How to Spec any truck with an Eaton Transmission; Select Desired RPM, Select Tire size and finally choose transmission gear ratio, 0.73 seems most popular. Hit "Calculate" and choose your ground speed, look to the left of the graph to see the corresponding rear-end gear ratio.
