The Aero X package on my new Cascadia includes the wheel aerodynamics buillt by Flow Below and designed specifically for Freightliner. The system is designed to improve the aerodynamics of the new Cascadia. Flow Below boasts a 2.23% fuel mileage gain for their standard system. Their testing backs the claim. The system on my new Cascadia has a larger surface area than the standard system and may improve the mileage even more. I can not back the claim with my personal experience. I have not tested the system seperately from the rest of my truck. My MPG has been over 9.
The system makes sense. Think of it as a flow around system. The least aerodynamic parts of the tractor and trailer units are the undercarriages. The idea behind the system is to keep the air from getting benieath the units. The system guides the air around the units instead. By sliding the air around the units, the drag coefficient is improved. The cross members under the trainers are designed to hold a tremendous weight. They are not designed to be aerodynamic. The less air that hits the cross members, the better.
The idea that the system saves fuel is completely logical. What worried me was the durability. I do a lot of drop and hooks. So far they have held up as promised. The dark rubberized pieces are extremely pliable. I was worried about the fasteners. They have been perfect. I have made no effort to not drag the trailer across the frame. I knew that I would eventually forget the system and raise a low trailer with the frame. I was impressed with the flexibility of the main composite. The gray pice bent, but then went right back into place. It is similar to how a vomposite trailer skirt works. It is pliable to bend when rubbing against a hard object, but stiff enough to maintainaerodynamic rigidity in the wind.
The next question is - is it worth it? Visit the website www.flowbelow.com. They have a fuel savings calculator built in. It is a useful formula for calcualting fuel savings from other aero products, such as trailer skirts or tails. Plug in your numbers. The clacualtor provides an annualized savings. I prefer to work on a per mile basis. You can easily figure that out from the formula. You know your operation better than anyone. Do your own math. Make your own decsisons based on objective data.