Does the spoiler on the Gen III Prius actually improve mileage(such as by breaking the airflow free of the car at the rear so it doesn't get dragged along behind the car) or is it there just to look cool and actually reduces mpg? My understanding is that a rear spoiler is intended only to push down on the rear tires and improve traction. But that is only at race car speeds, which is antithetical to a Prius. Having spent all the effort to reduce drag on the Gen III from .26 to .25, I can't imagine they would put anything on it just to look cool or that was counterproductive to mpg. Also, why aren't the windshield wipers covered by the hood. Seems like they would create a lot of turbulence. Finally, is the Gen III hubcap actually aerodynamic, or does it create a lot of unnecessary drag. Perhaps a solid disc shape would not permit enough airflow to cool the brakes.
I believe the spoiler and the hubcaps are both there for aerodynamics, as are some other components, but I look forward to hearing from some of the experts in this forum.
I would not expect an increase in mpg by adding a spoiler to the prius. In fact you may get worse gas mileage because of the extra weight and drag that the spoiler would cause. Spoilers work well in high performance race cars travelling at fast speeds.
I expect there is nothing on the Prius that would significantly increase the cd. They have gone to a lot of trouble and expense, i.e. under body and under engine covers, plastic wheel covers over alloy wheels, etc, and it seems unlikely they would spoil the low cd with a spoiler that provides drag. I expect the spoiler on the hatch breaks up the air flow as it leaves the rear of the car and actually lowers aerodynamic drag. Granted, spoilers on race cars are frequently used to provide down force and to do so produce a lot of drag, their use in that respect is a trade off of cornering and braking forces vs a low cd. But there are some aero gadgets on race cars, where the rules permit their use, that enhance the air flow over certain parts of the car. Take a look at this: Formula 1 I doubt the spoiler on the Prius is functionally anything like the add on spoilers people bolt to the trunk lid of their Civic.
I have not ridden in a Gen III, but in a Gen II. the spoiler helps keep rain off the upper rear window. It almost never gets wet over 30 MPH. (I suspect it has other aerodynamic effects, but I like the clear rear window)
I supposed some could say that the spoiler is there to have a place to grab to close the hear hatch. I have no clue as to what the design engineers were thinking, but I could see how it effects aerodynamics and/or design.
+1 I can't remember or find where I read it now but the major factor contributing most to the Prii's low CD is the way it reduces the vacuum or drag at the rear of the car. That spoiler is a big piece of that. It went into a discussion about boat tail style bullets, etc. If you cut a boat tail bullet in half long ways it sort of looks like a Prius. I'll keep searching for it but it was an interesting read. Bugs me when my search foo is weak.
The term "spoiler" has multiple meanings. In its true form, a spoiler is a turbulence inducing strip that spoils the lift on an airfoil. They are used on aircraft to reduce lift when landing, and to control the stall characteristics of a wing. On a Prius, the spoiler serves the same purpose. It produces turbulence that spoils the airflow over the back of the car. This enhances the Kammback design of the Prius, helping it slip through the air. Smooth airflow over the back produces lift in the wrong direction, which adds to the drag. The turbulent bubble of air behind the car effectively produces a longer, more streamlined shape with lower drag. The other common use of the word "spoiler" is for an inverted wing used on race cars. This is not a spoiler in any sense of the word. It is an airfoil, and it trades drag for downward force, which is a good trade when you have excess power but not enough cornering friction. This use is completely unrelated to the Prius. Tom
The spoiler is part of the Kammback design, to enhance the Kamm effect. You need an abrupt cut off so the air flow continues to flow backwards cleanly, and that reduces surface drag & turbulence.
The others have mentioned it. It's more for managing air flow out the back of the car. The aerodynamic wheel covers are there to minimise turbulence around the wheel (Kinda of a compromise between the near full disc like the Civic Hybrid and a design with *some* style). As a by-product of that, it helps reduce weight as they can use less metal alloy and use lighter plastic to create the wheel design they want. Also, I believe the wipers are reasonably sheltered from the wind. Crouch down from the side and imagine air flowing over the hood. I suspect the wipers are out of the air flow due to the angle of the hood even though they're not as hidden as on some other cars.
I like the fact that it will block the headlights of cars following at night if the proper distance is maintained. Aloha, ED
