For aerodynamic fuel economy, the Cascadia is a leader. Plus it offers maintenance ease, comfort, power and durability.
Since the introduction of Kenworth’s T600 in the 1980s, manufacturers have been refining the aerodynamics of the conventional tractor. A wind-cheating design has become critically important given that at speeds above 50 mph, the effort in pushing the wind aside is the major contributor to marginal fuel use.
To develop the Freightliner Cascadia, Daimler Trucks designed its own wind tunnel in Portland, Ore. More than 2,500 hours were spent testing and redesigning using full-size models to create the new tractor. Since then, the Cascadia has been back in the wind tunnel to make it possibly the most aerodynamic truck ever on America’s highways.
The extension of the fender line into the doors is no styling exercise, though it does make the Cascadia distinctive from the side. More importantly, flowing lines help manage the airflow along the cab and sleeper. Lately, the visor is back as an option, though it performs a useful function in helping move the air over the rooftop. Side extenders have grown a little to keep the air flowing smoothly onto the trailer sides.
From the front, with that huge grille accommodating a 1,625-square-inch radiator, you can’t miss a Cascadia. Form and function are at one: The big opening draws in as much air as possible to minimize fan-on time, in turn reducing parasitic draw on the engine and boosting fuel economy.
The Freightliner I tested featured the Detroit DD15 at 475 hp and 1,650 lb.-ft. of torque. It was backed up by an Eaton FRO-16210C 10-speed transmission.
It came from Los Angeles Freightliner in Fontana, Calif., on Valley Boulevard. Valley has to be one of the worst pieces of pavement anywhere, so the first surprise was how comfortable the ride was as I bobtailed to pick up a new Utility reefer. I continued to be impressed with the smooth ride as the Cascadia coped with rough concrete when I headed out I-10 westbound and then to I-15 toward the high desert.
Another excellent feature was the sporty shifter Freightliner engineered for the 10-speed. It had a close gate with short throws, but it was not in the least heavy. It was as good as a Kenworth’s, and that says a lot. Good throttle modulation meant little difficulty with the gears, whether clutching or float-shifting the transmission.
As with all modern truck diesels, the DD15 has excellent clutch engagement torque and needs no throttle to get the truck moving. Then almost no foot-feed is necessary to get to speed. Going through low range, 900 rpm was all that was needed. Flicking the range-change up, and pulling the shift lever left and back to pick up high range, no more than 1,400 rpm was necessary to get to freeway speed.
The two-turbo design of the DD15 is not unique to American big-bore diesels, where series turbocharging has become almost commonplace. The difference with the Detroit, though, is that downstream turbo actually provides power to the flywheel through a reduction gear. The upstream turbo provides the air for the engine by way of a charge cooler. Since the downstream turbo-compound power requires its own backpressure, the engine turbocharger needs no complex variable geometry to recirculate the exhaust.
The contribution of the turbo-compounding makes an additional peak 50 hp available and the result is a real kick in the pants when you press the accelerator: The DD15 builds torque far faster than any comparable big diesel. It feels more like a 550- or 600-hp engine when you initially mash the throttle.
This also makes the DD15 a good engine for freeway overpasses that can pull down speed as you need it. With the Detroit, the response is immediate and speed is maintained.
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