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| Running in "clean air" allows for the best use of all of my areodynamic devices . |
Have you ever heard NASCAR commentators talk about how the air off one race car has a direct effect on another car?
Terms such as clean air, side drafting, drafting, taking the air off another car and aero push all have to do with how the air flows over a cars body and effects performance.
Many of the factors above have an influence on how our trucks perform as well. I once had an engineer accompany me along in my truck for a week. We talked about how I can distinguish if the vehicle passing me is a car, pick- up truck or another large truck. It’s quite easy for me as it greatly affects the fuel mileage indicator in the center of my gauge cluster. For example, if a large truck comes up from behind me and closes in on the rear of the trailer, my fuel mileage will increase. The reason for this is that the high pressure in front of their truck fills in the void behind my trailer. When the truck behind me turns out into the passing lane my fuel mileage decreases. If the truck should decide to pass, I’ll see a variation of dips and spikes in the fuel mileage. As the overtaking trucks front bumper gets next to my trailer tandem, the fuel mileage decreases. This occurs even more due to the wake of air off his front bumper which pushes in between the tandem axles of my trailer. As the overtaking truck continues to pass beside the trailer skirts, the fuel mileage begins to rise a bit. At this point the wake of air from the passing truck is hitting the flat sides of my trailer and side skirts. As the passing truck progresses forward, the mileage will dip once again as it approaches the tractor tandem and trailer gap. Once again, this is due to the wake of the overtaking trucks air being forced into the tractors tandem axles and trailer gap. Once the trailer gets next to your cab, you’ll feel the vacuum of air pulling your truck towards the overtaking trucks trailer. In NASCAR, this is called “side drafting.” If you have a fuel mileage indicator in the dash cluster, you’ll notice a rapid increase in fuel mileage. This is due to the fact that you are behind the wake on the leading edge of the overtaking vehicle which puts you in a vacuum. Once the truck and trailer do a complete pass, you will notice a mileage increase as this truck is now breaking the air for your vehicle.
Other observations in regards to air flow are that the more aerodynamic and smaller the vehicle overtaking you… the less effect you’ll see on your fuel mileage. A car carrier passing you causes you much more fuel mileage disruption than if you are passed by a small sports car. That same car carrier however is great to follow as they poke an enormous hole in the air. Your truck doesn’t even need to be in close proximity in order to reap the benefits of its air flow. In NASCAR, this is called “catching the draft.” Oddly enough, a vehicle that is much smaller yet pokes a big hole in the air is the large fifth wheel camper pulled behind a pick-up truck. Once again, from quite a distance back, you can still reap the benefits of its air flow.
There are many other examples which I could go into, however the lesson that I’ve learned over the years is put into consideration upon whether it’s advantageous to make the move to pass or not to pass the vehicle in front of me. The last thing you want is to get into a long drawn out pass with the vehicle beside of you. This is often referred to as a “turtle race.” My favorite condition is to be operating by 
myself in clean open air. This allows all of the aerodynamics on my truck/trailer to operate exactly as they were designed.
Lastly, please don’t tailgate in order to make any of these observations.