Petevb

I don't know that I'd separate the two issues as you're trying to do, as they are entirely inter-related for two reasons. First, to generate total downforce you need to cancel out any lift that is created. Second, the angle and condition of the incoming airflow to the rear wing largely determines how difficult it is for the wing to create downforce.

A wing's job is to "turn" incoming airflow, redirecting its path- it must do this in order to create lift or downforce. However if the air is already turned, as on the back of the early 911, then the car is acting as a wing itself. The wing needs to "turn" the air back to cancel this out, which is difficult because it needs both a lot of redirection and because it's already quite turbulent before it gets to the wing, meaning the wing can't function efficiently. This is fake, but it's exactly why it's hard to make downforce on an early 911:



And why it's easy on a modern 991:


Hence I don't think you can talk about the difficulty in generating downforce on a 911 rear without discussing the rear rake, etc.

In reality it's actually not hard to make rear downforce in either case- put a big enough wing on the back and the rear is going down. Making downforce efficiently or at the front is a very different matter, however.

Nizer

Got it. Now when the rear wing snaps off my Cup going up through the esses at The Glen and I have an intimate encounter with the blue bushes I will blame it on a sudden and dramatic reduction in negative lift as opposed to a loss of downforce. Wait, crap! I think that's a redundant statement. Or am I just being pedantic? I'm confused.....

mgent

Isn't downforce generated by the flow of air of the underside of surfaces more than the top side, and management of flow on the top side generally to manage drag?

If that's correct, there could be fairly significant gains by changes on the underside of the car - splitter, floor, diffuser - that are not really visible on the test mules... I'm not smart enough to gauge the magnitude of any potential changes, but that could drive significant downforce resulting in the changed tire load rating..

That being said, I would expect the 918's clean sheet design to take advantage of more of these areas than a package on an existing car...

cbweaver1

Correct, more down force than on a 918 hence the higher sidewall ratings. Final design on rear air inlets with mesh a la the RSR will have a dual purpose: feed more into the motor than standard GT3 while an additional internal opening near the rear tires will create negative pressure reducing underside lift in order to generate more down force. The front vents are in place to do the exact same thing near the front tires to even out the balance. It is not on the Cup (for the moment) but it is not a gimmick either. There will be no one "killer" aero element as on previous GT3's (massive rear wing) to get massive down force but rather the sum of the parts, their design and specific location on the 991 RS which will separate it over the standard GT3 more so than any previous iteration before it.

How do I know this? The same little birdie that told me exactly what we are seeing and hearing on the test mule over a year ago while sipping on a cappuccino. They will sell every last one of them and at a premium.........

paver

Ask the little birdie when its debut is.

Petevb

It can be either. Generally the biggest improvements in lift to drag ratio can be found on a car's underside, if practicalities and rules allow changes there. Often they do not. The trend recently has been to do more with the underside.
They are certainly doing some of that, but there are always telltales when they do. The issue is that making downforce with the underside requires getting air that gets under the car out, so you look for the diffusers, vents, etc.

In this case a telltale is the fender vents- modern cars use variations of those to improve front downforce by removing air from behind the front wheel into a low pressure area. These vents take different forms- on the 918 there are multiple vents in the flank behind the front wheel:

Similar on the La Ferrari and P1, they remove air from under the front of the car to turn that into a low pressure area:

The fender vents on the RS will be performing a similar function- that's how they are getting air out under the front, so we can guess there is some trickery going on under there.

In back you would traditionally look for a diffuser, but as we've said there is a motor and exhaust in the way of anything large, blocking the direct exit path. Alternatives are behind the rear wheels, either with wheel arches cut away or with fender vents. Looking closely at the rear flanks of the red model's bumpers it does look like there could be quite a large vent in that location- if so that would do it. You can see a similar but less sculpted feature on the RSR in the location you'd be looking at:


And you can maybe see something like it below:

Petevb

Sounds very much like your source gave you good info...

<3mph

Thanks, everyone, for the really great info. I have learned so much from reading your posts! Please keep discussing!!

TRAKCAR

I want it Big *** Downforce.

Z356

I am with you, brother!

Saludos,
Eduardo
Carmel

.

Zucc

Definitely a Turbo!

0Q991

Not sure if posted already:

http://www.carmagazine.co.uk/Secret-...patent-photos/

Pretty clear look...

Nizer

Nope. Nice find!

Bill_C4S

+1 and thank you!

CAlexio

Among other things, I love how the rear deck is black all the way down past the glass, as well as the flaps" that are created at the sides of the rear bumper..

Ok, so the big question.. What should they/can they charge for this now over the gt3?