How much is gained from the standard spoiler

[luxury1]

The automatically rising spoiler is a really cool function of the box and definitely makes the car unique but how useful is it especially at lower speeds? I could see that there might be some lift over 100 mph but at 75 it seems a little unnecessary. Does it rise at these somewhat lower speeds to actually combat lift? Just curious...

[MNBoxster]

Originally Posted by luxury1

The automatically rising spoiler is a really cool function of the box and definitely makes the car unique but how useful is it especially at lower speeds? I could see that there might be some lift over 100 mph but at 75 it seems a little unnecessary. Does it rise at these somewhat lower speeds to actually combat lift? Just curious...

Hi,

The Boxster actually gets pretty light at around 75MPH, something like 110lbs. in the rear.

The Spoiler is actually a true spoiler and unlike a Wing, does not create any downforce to control lift. The difference is subtle, but distinct. The Wing counteracts lift, while a Spoiler prevents it.

Lift happens because of the Pressure Differential between the Air flowing over the Top and the Air flowing under the Bottom surfaces of the Car. Air pressure under the Car is increased as the Air slows, piling into itself, trying to flow between the Car's underside and the Ground. The Air over the Top on the other hand moves much faster and so has lowered pressure relative to the Air trying to flow underneath. The difference between these two pressures is what causes lift.

By extending the Spoiler, the airflow on Top is literally Spoiled, that is, it is blocked and slowed down and it's pressure rises to come into equilibrium with the Air flowing underneath, consequently, no lift is created. Wings on the other hand, exert a downforce to counteract the lift created by this Pressure Differential rather than preventing it.

Wings are, at a point, more efficient than Spoilers and so these are preferred for truly high speeds, such as a race Car. Hope this helps...

Happy Motoring!... Jim'99

[Brucelee]

Jim,

Is this theory or have you seen lab data on the Boxster wing? Frankly, to me, it look like a POS up and not effective at all.

And, I have no data on it either.

[MNBoxster]

Originally Posted by Brucelee

Jim,

Is this theory or have you seen lab data on the Boxster wing? Frankly, to me, it look like a POS up and not effective at all.

And, I have no data on it either.

Hi,

I have seen such data, but I cannot remember the source, I may be able to locate it in a day or two, I do remember that the Rear experienced lift in excess of 100 lbs. though.

Be careful about using the word Wing to describe the Spoiler, because that's what it is a Spoiler, these are two distinct things and perform very different functions, the terms are not interchangeable. A Wing is really an inverted Airfoil which generates Negative Lift (DownForce) while a Spoiler slows down the Airflow (or Spoils it) by disrupting it and consequently increases it's pressure. Although the end result - increased Rear-End stability, is the same, it is arrived at using two entirely different methods.

One need only disable the Spoiler and run up to high speed to feel the lightness which the Car's Rear experiences. I do not advocate doing this in Traffic as the Car does become quite unstable. Anyone interested in such an experiment should do so on a Track or at least a deserted stretch of Road...

Happy Motoring!... Jim'99

[Ronzi]

Info I have seen in Brian Long's book "Porsche Boxster" says the spoiler is capable of "Reducing rear lift by up to 30 percent ...".

[mach schnell]

i'll post a thread later today about a 300 mile loop I did yesterday that included a zip through the soCal desert (Coachella Valley) where the cross winds across the open desert are significant - I'll post about my impressions of the car at high speed including potential difference in feel prior to 75 mph and above 75mph. Sorry for the tease, but gotta go do some other things right now. The thread will be up by early evening PST.