Do I need a front Splitter if I get a functional Spoiler?

[JAS550]

Except for those of use who have the CS. We have a bigger splitter than the pp but don't get the same belly pan as the pp.

Oh yeah, forgot about the CS splitter.

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[Sal33n]

What's nice about the CS splitter is you can use it on a non pp car.

 

[GTP]

From what I understand (engineering degrees but not a formal aerodynamicist), as a car reaches high speeds, a high pressure "bubble" forms in front of the windshield, and thus shifts the aero balance forward. By quite a lot.

What scares me is the scenario of jamming on the brakes above 130mph. I imagine the car wanting to swap ends. Look at a Corvette with its tall rear air dam. More drag but it balances the aero.

In summary, I think that the downforce of a true rear wing greatly exceeds that from a front splitter. And that makes it a highly desirable and functional add-on.

My question is: Does a Roush spoiler add much rear down force at all?

 

[ghostnote]

From what I understand (engineering degrees but not a formal aerodynamicist), as a car reaches high speeds, a high pressure "bubble" forms in front of the windshield, and thus shifts the aero balance forward. By quite a lot.

What scares me is the scenario of jamming on the brakes above 130mph. I imagine the car wanting to swap ends. Look at a Corvette with its tall rear air dam. More drag but it balances the aero.

In summary, I think that the downforce of a true rear wing greatly exceeds that from a front splitter. And that makes it a highly desirable and functional add-on.

My question is: Does a Roush spoiler add much rear down force at all?

No spoiler adds down force. It reduces lift. The net effect of it, though, is equivalent to added downforce. But you'll never get positive downforce at the rear end. For that you need an airfoil, like the GT350R's wing. Something that lets air go up and under.

These might seem like disjointed statements. A simple example should clear it up. At zero speed, you have zero force on the rear end. At 80, on the car without a wing, you have a flat surface on the bottom and a curved surface on top. The air going over the car will follow the curve and, at the end, it will turn downwards. For every force, there's an equal and opposite force applied. This is lift.

So how to get rid of lift? You add a spoiler, which functions as a dam preventing the air from following the curve down the trunk. (Insert very complicated fluid dynamics arguments here, including references to the navier-stokes equations and technical stuff like "vortices," etc.). At best, you're back to zero force. No lift. Which in the end, is equivalent to some downforce when you consider that the lift is canceled.

Now with a wing, you can actually redirect some of that air upwards - and this is actual downforce.

Now, with regard to the whole point of this post: if the car is balanced at low speeds, you don't need a splitter to go with a spoiler. It may actually make the car front-biased at higher speeds (say 130+ mph) - because you'll be making downforce up front, but not at the back. So the balance will change.

Now, if you have aero aids at front and back, the downforce available will change as you go faster. If you have your setup right, the car should feel the same (if not stickier) at higher speeds.

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