As many of you know, I started a project called 70+/10. The goal of this endeavor is to work towards averaging double-digit fuel economy averages, and travel at the posted speed limit up to 75 mph where safe, legal, and applicable.
Of course, many of you will ask “Why limit yourself to 75 mph when there are speed limits in excess of this number?”. The reason I chose 75 mph as the high-end limit, is because the weakest link in this scenario is the tire. Most tires are only rated for 75 mph and in fact, you’d be surprised by the number of tires that have a 60 mph rating.
This project started over 500,000 miles ago with my 2017 Cascadia which we called “New Blue”. New Blue is a Cascadia AeroX powered by a Detroit DD15 400HP/1750 FPT @ 975 RPM DT12 direct drive automated manual transmission, Detroit rear axles with 2.16 rear axle ratio, along with active lube management. There were many times that our 2017 model attained double-digit fuel economy numbers at speeds up to 72 mph. The lifetime average for New Blue was 9.5 mpg, and for the duration of this project was 9.2 mpg. Early in New Blue's career, I had pretty much limited her speed to 65 mph and had exceeded the 10 mpg mark. In itself, that was quite an accomplishment.
Now, here we are today with our 2022 Freightliner Cascadia “Celeste”. This truck is equipped with all of the latest aerodynamic enhancements offered by Freightliner, along with a Detroit DD15 455/1850 FPT @ 900 RPM, followed by a Detroit DT12 .78 overdrive automated manual transmission coupled to a Detroit 2.61 rear axle ratio, and active lube management. This truck is also a 6x2 with a Hendrickson OPTIMAAX liftable pusher axle. For this truck with the overdrive transmission and the 2.61 rear axle ratio, the overall ratio equates to 2.03.
We built this truck to be versatile and handle a wide variety of loads. This is why I employ a lift axle on the truck, as well as on the trailer. When lighter loads permit, it only makes sense to not have more axles on the ground than necessary. By doing this, it promotes better fuel mileage, more even tire wear, and in some places, reduced tolls.
Let's get on to the results so far. Our first load with this truck weighed in at 78,500 GCVW, which didn’t allow us to take advantage of lifting axles. The only advantage this system enjoyed, was the fact that it was a 6x2, which takes the parasitic loss of a differential and power divider out of the equation. Our first trip yielded 8.8 mpg with a heavy load in Christmas holiday traffic. Since then, we’ve had many loads where we’ve been able to take advantage of the lift axle on the truck, or on the trailer, and both in some cases. To date, with 18,500 miles on the odometer, the lifetime average is 9.951mpg, with the highest mileage for a tankful coming in at 11.091 mpg, and the lowest at 8.862 mpg. All of this was achieved by cruising at speeds up to 75 mph. In most cases, 75 mph is posted as a large portion of our normal route.
I’m very pleased with the versatility I’ve experienced with the Detroit Powertrain, along with the enhancements that the Hendrickson OPTIMAAX liftable pusher axle offers to our operation.