|
They DO work.....
Here's why....
At lower speeds, they force air down and keep dust, gravel, exhaust fumes away from the back of the vehicle. They were originally designed just for dust, but manufacturers in the 70's and 80's discovered that they also work on exhuast fumes. Stationwagons that had tailgate windows that could roll down would suck them in, so they were installed so that the occupants would not choke on exhaust fumes and potentially pass out from CO2 poisoning.
BUT, at higher speeds, the liberty (and any other large "flatbacked" vehicle) creates a vacuum with its passage through air on the back of the vehicle. Air goes around the vehicle, but swirls and cavitates in an effort to fill the empty space near the back of the window. Its a fruitless effort, and the volume of air that you disturb and tow along with you is three times as big as the liberty itself. The net effect of this is that the faster you go, the more air you "pull" along with you, and this decreases gas mileage exponentially. Think of it as a parachute.
What this thing does, however, is force fresh air down into this vacuum, effectively filling it with a large enough volume of air that the vacuum is neutralized. At speed, this creates a large self-replacing air pillow attached the back of the vehicle, in which air coming around the vehicle just slides off on all sides.
Mythbusters did this and proved that it is in fact "confirmed." Also, my physics professor did a similar experiment with a smoke chamber and the smoothness of airflow with it was phenomenal. The pitch (or angle) of the wing can be altered, but most manufacturers choose the angle to be most effective at highway speeds. The pitch the Mopar wing uses is most effective between 68-80 mph, right in the highway zone.
So yes, it does work great. Get one.
PS This is essentially the opposite of a spoiler. A spoiler on a rear drive car (like Nascar) forces air up in an attempt to create more "weight" or downforce on the back of the car for more traction. It does this because the pressure to displace air upward, when it wants to go down, produces downforce. What it also does is create a much larger vacuum in each vehicle, so when you hear the term "drafting", you will know that this means one car is getting into the vacuum of another car, and is being sucked forward along with it! The physics of 200mph, however, dictate that it is more beneficial to create drag and downforce, rather than lift and reducing vacuum drag.
This deflector does the opposite. It forces air down, filling the vacuum instead of making it bigger. The physics of highway speed dictate that an wind deflector would be more beneficial. Technically, it does reduce the weight on the tires, because the deflector is actually pulling up on the vehicle at speed. But at over two tons, I don't think she'll get airborne any time soon!
_________________
2003 Jeep Liberty Freedom Edition
3.7L 5-spd 4x4, Rusty's 2.5 in. coil lift
General Grabbers AT2's 245/75-16E on MOABS
EVIC installed, iPod wired, Hella 500's and Grilles
Mopar Bike Rack, Mopar Roof Rack, Black Widow Roof Basket w/ air deflector
Draw-Tite Hitch, Front Tint, Debadged on sides and front
|
Login
Register
FAQ
Search
