I remember we discussed this a while back and there was a little bit of confusion on what the actual force numbers of the spoiler were. I ran across this in a DC press release about the Crossfire:

I ran those numbers through a conversion calculator for those of us who don't speak metric and that works out to 80 lbs of downforce at 80.1 mph.

 

The confusion came from the service manual and other DC literature, which states that the spoiler creates 40 lbs. (356 N.) of downforce at 80 mph. Obviously, DC screwed up on the conversion.

 

just like the spoiler activation speeds, or the engine oil capacity

 

Bobs: Good info to have, thanks for the research. Now I can take that dead body out of the back of the car when I race...

 

Bobs, thanks for clearing that matter up. I'm guilty of posting that 40 lb. reading several times, simply because I read it somewhere. But when I went back and re-read the several different magazine road tests that I have on the XF, I couldn't find it. The only reason it stuck in my mind was because I thought it was a little low, as if the same thing could be accomplished by lugging a couple of adult sized bowling ***** around.
Now if we could just find out what the SRT-6's spoiler statistics are, we'd have grounds for an entirely new thread.

 

I will show my Physics-related stupidity here, but wouldn't 80 pounds of down force be very different from carrying an extra 80 pounds of weight. It seems to me that inertia and such would come into play - just not sure how...

 

If you are traveling at a constant speed of 80 mph, it would have the same effect on handling assuming you had the weight positioned correctly in the car. I don't think the added drag from the deployed spoiler would be enough to affect the handling. At any other speed, the spoiler will produce different amounts of downforce, so you'll get different handling results. As far as acceleration, you would get different results depending on how the added inertia of the weight compares to the added drag from the deployed spoiler.

 

I'm certainly not a physicist and I have no idea what effect the spoiler has on performance, other than it just looks cool, but I suspect the spoiler has a different effect on a coupe than a convertible. On the coupe the air flows over the roof, like a wing, when the spoiler is deployed it [like the flaps on a wing] extends the area of the roof which increases the drag, however when you extend the flaps on a wing it creates a greater low pressure area above the wing and increases lift. That's why you deploy them, you get greater control [lift] at slower speeds.

On the convertible [with the top down] you sit inside the area of low pressure, which is why the air is reasonably still in the drivers compartment at high speeds and when the spoiler is deployed it disrupts the airflow allowing a high pressure area to form immediately behind the car reducing drag.

I suspect that the spoiler may be more effective on the roadster than the coupe. Of coarse after trying to figure out how to explain this and reading how ridiculous this sounds, well - never mind...

 

Flaps extend the top area of the wing to provide increased lift. A spoiler is kind of like an "anti-flap". It is used to decrease or "spoil" the lift that a wing generates. It does that by popping-up and interrupting the high-speed airflow over the top of the wing. You can see this when an aircraft is landing. As soon as the wheels touch the runway the pilot will pop the spoilers up and activate the thrust reversers on the jet engines to kill lift and reduce speed as quickly as possible.

Our spoilers are angled just right to kill some of the lift that the body produces and also collect enough high pressure air on their top side to add some useable downforce without adding too much drag.

If you're interested, here is a link from NASA's Beginners Guide to Aerodynamics that shows what I'm talking about.