Consolidated 991RS thread
#1171
The unanswered question is whether the 991 RS will make more downforce than the 918, thus mandating a higher load rating tire. Even with all the refinements and aero tweaks over the years, I'm somewhat skeptical given the 918 is a clean-sheet design whereas the basic 911 shape is 50 years old. And let's not forget that the 991 RS will on the order of 600lbs lighter than the 918; an approximate 15% static weight savings
We at least know enough from the 991 Cup to safely assume the 991 RS will make more aero than the 997.2 RS.
We at least know enough from the 991 Cup to safely assume the 991 RS will make more aero than the 997.2 RS.
High downforce isn't difficult to achieve if you're willing to take a drag penalty- see the RSR or the aforementioned Viper ACR, quoted at 1200 lbs at 150 mph, though in practice almost certainly less. Bolt on big wings and you'll make downforce, it's just mileage and top speed that will suffer. I now expect the RS to have lower top speed than the GT3, have a worse lift to drag ratio than the 918, but make boatloads of downforce. I could easily be wrong- we don't even know if the tire numbers are accurate- but that's where I'd put my money.
As far as the design, aerodynamically the current 991 generation has about as much in common with the original 911 as a bird does with a brick.
#1172
Rennlist Member
Pete. Ive been asking around an although most of my PAG contacts have been quiet since the "GT3 Action Group" time, its been confirmed to me that the picture below of the Minichamps 1:43 model is indeed 100% cosmetically accurate to the final customer cars we will see shortly launched to the public. To get the type of down-force you refer to I would have thought perhaps front dive planes would be required? the 991 GT3RS is clearly wider at the front and rear axles than the 991 GT3 with conforming bodywork. The wheels on the model are clearly staggered sizes and again confirm what I have been told which is that the wheel design is identical in style to the existing GT3.
I think downforce and grip will definitely be increased significantly. It will be fun to finally find out!
I think downforce and grip will definitely be increased significantly. It will be fun to finally find out!
#1173
Three Wheelin'
The RS has tire load ratings 10% higher than the 918 despite being 15% lighter, so yes, I think it will have much more downforce.
High downforce isn't difficult to achieve if you're willing to take a drag penalty- see the RSR or the aforementioned Viper ACR, quoted at 1200 lbs at 150 mph, though in practice almost certainly less. Bolt on big wings and you'll make downforce, it's just mileage and top speed that will suffer. I now expect the RS to have lower top speed than the GT3, have a worse lift to drag ratio than the 918, but make boatloads of downforce. I could easily be wrong- we don't even know if the tire numbers are accurate- but that's where I'd put my money.
As far as the design, aerodynamically the current 991 generation has about as much in common with the original 911 as a bird does with a brick.
High downforce isn't difficult to achieve if you're willing to take a drag penalty- see the RSR or the aforementioned Viper ACR, quoted at 1200 lbs at 150 mph, though in practice almost certainly less. Bolt on big wings and you'll make downforce, it's just mileage and top speed that will suffer. I now expect the RS to have lower top speed than the GT3, have a worse lift to drag ratio than the 918, but make boatloads of downforce. I could easily be wrong- we don't even know if the tire numbers are accurate- but that's where I'd put my money.
As far as the design, aerodynamically the current 991 generation has about as much in common with the original 911 as a bird does with a brick.
Just guessing here: Perhaps Porsche has finally figured out how to add aero downforce with diffuser technology?? The rake of the wing on the 991 RS videos is not that great. By using the side scoops to run air into the engine compartment, and exiting out the rear low, maybe they have finally figured out how to keep engine airflow adequate, and use efficient downforce methods to not increase drag? just thinking outside the box, as the overall design of what we have seen so far is not that much different than the gt3, besides the air scoops.
#1174
Macca,
Dive planes were on the most recent test mules. I think they are likely to be added to the final design. Porsche is probably just trying to finalize the aero.
I can't wait for this thing. If the 918 seats are available for the US cars (as seen in the model above), then I doubt I'll be able to resist.
Dive planes were on the most recent test mules. I think they are likely to be added to the final design. Porsche is probably just trying to finalize the aero.
I can't wait for this thing. If the 918 seats are available for the US cars (as seen in the model above), then I doubt I'll be able to resist.
#1175
Rennlist Member
Jon. You are right., That is a very recent addition to the testing mules. I wonder indeed if it will make it into production. I guess the design team have had a little more time on their hands for the RS than is typical this time around...
#1176
Rennlist Member
It does look very close to production ready this recent mule doesnt it...just ear away the camo over the roof and front fender vents and you are basically there...
What we see here is a 90% finished proto. The cover over the hood is a red herring I feel and no hood treatment exists (although the hood itself may be composite). There are vents above the front wheels on the fenders both sides of the car which are clearly covered with camo. The roof is double bubble likely composite. The rear spoiler isnt a production ready item but in this example the wheels look to be. The dteering wheel will feature a yellow centring strip before presentation and teh car will feature light weight one piece bucket seats in nomex fabric at least for ROW supply. Door cars will be simplified and lighter. Brakes will be steel (possibly 410mm) with PCCB as an option. The front dive planes are new and may or may not make the production variant. The hard formed panels on this mule including front and rear bumpers look to be final items sans camo IMO....
What we see here is a 90% finished proto. The cover over the hood is a red herring I feel and no hood treatment exists (although the hood itself may be composite). There are vents above the front wheels on the fenders both sides of the car which are clearly covered with camo. The roof is double bubble likely composite. The rear spoiler isnt a production ready item but in this example the wheels look to be. The dteering wheel will feature a yellow centring strip before presentation and teh car will feature light weight one piece bucket seats in nomex fabric at least for ROW supply. Door cars will be simplified and lighter. Brakes will be steel (possibly 410mm) with PCCB as an option. The front dive planes are new and may or may not make the production variant. The hard formed panels on this mule including front and rear bumpers look to be final items sans camo IMO....
#1178
Pete. Ive been asking around an although most of my PAG contacts have been quiet since the "GT3 Action Group" time, its been confirmed to me that the picture below of the Minichamps 1:43 model is indeed 100% cosmetically accurate to the final customer cars we will see shortly launched to the public. To get the type of down-force you refer to I would have thought perhaps front dive planes would be required? the 991 GT3RS is clearly wider at the front and rear axles than the 991 GT3 with conforming bodywork. The wheels on the model are clearly staggered sizes and again confirm what I have been told which is that the wheel design is identical in style to the existing GT3.
The 911 has it relatively easy vs most cars, as you're generally limited by front downforce, and the 911 needs to make relatively less as it has less weight forward. This means it can make higher total downforce vs something like a Vette for a given setup. The front is significantly more aggressive than the GT3, so downforce is well up, but it's hard to say how much...
Assuming the louvers are covered, the front dive planes might be temporary, making up for lost front downforce so the car can be tested with correct aero balance.
Last edited by Petevb; 07-30-2014 at 09:14 PM.
#1179
The RS has tire load ratings 10% higher than the 918 despite being 15% lighter, so yes, I think it will have much more downforce.
High downforce isn't difficult to achieve if you're willing to take a drag penalty- see the RSR or the aforementioned Viper ACR, quoted at 1200 lbs at 150 mph, though in practice almost certainly less. Bolt on big wings and you'll make downforce, it's just mileage and top speed that will suffer. I now expect the RS to have lower top speed than the GT3, have a worse lift to drag ratio than the 918, but make boatloads of downforce. I could easily be wrong- we don't even know if the tire numbers are accurate- but that's where I'd put my money.
As far as the design, aerodynamically the current 991 generation has about as much in common with the original 911 as a bird does with a brick.
High downforce isn't difficult to achieve if you're willing to take a drag penalty- see the RSR or the aforementioned Viper ACR, quoted at 1200 lbs at 150 mph, though in practice almost certainly less. Bolt on big wings and you'll make downforce, it's just mileage and top speed that will suffer. I now expect the RS to have lower top speed than the GT3, have a worse lift to drag ratio than the 918, but make boatloads of downforce. I could easily be wrong- we don't even know if the tire numbers are accurate- but that's where I'd put my money.
As far as the design, aerodynamically the current 991 generation has about as much in common with the original 911 as a bird does with a brick.
#1180
Could a higher load rating be as a precaution, expecting these cars to see longer periods of track time, adding to the life of the tire (not specifically tread life) and ability to withstand more abuse or higher temperatures?
A question I want to research: with other cars, even other manufactures, do load ranges change from base model to the most powerful model?
A question I want to research: with other cars, even other manufactures, do load ranges change from base model to the most powerful model?
#1181
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997.2 GT3 F: 91 R:102
997.2 RS F: 93 R: 105
991 GT3 F: 91 R: 103
991 RS F: 99 R: 108
What's interesting here - remember these numbers are preliminary and could be full of inaccuracies - is the relatively even front/rear load rating increase (+2/+3) for the 997 RS over the 997 GT3 vs the relatively larger jump in front load rating for the 991 RS over the 991 GT3 (+8/+5). Comparing RS to RS the increase is +8/+3 front/rear. This suggests that if these factors are related to aero gain then there's more happening at the front than the rear for the new RS over the base model. This makes sense given the visible changes, with the rear wing very similar to that on the 997 RS, albeit a bit wider, while changes at the front include a deeper spoiler, fender vents, and potentially dive planes.
Another interesting thing to note, again assuming these numbers are accurate, is that the 997 GT3 front tire carried the same load rating as the 991 GT3. One would think that if these load factor changes were purely aero driven then the wider front end of the 991 GT3 would require a higher load rating tire vs the 997 GT3, all else equal.
As for bricks and birds, I haven't done much work with either so I can't speak to the comp. My point on the 911 shape vs clean sheet is that the basic 911 shape of downward sloping tail - still present today, albeit highly massaged and modified - is not inherently good at generating downforce. Hence the reason why all modern RS models and modern 911 racers sport monster wings where many of their competitors not married/handcuffed to the basic 911 shape can generate adequate downforce without them. That same relatively unchanged shape also limits the ability to incorporate underbody aero such as venturi or diffusers effectively. But I suspect you know all this
#1182
Three Wheelin'
Pete. Ive been asking around an although most of my PAG contacts have been quiet since the "GT3 Action Group" time, its been confirmed to me that the picture below of the Minichamps 1:43 model is indeed 100% cosmetically accurate to the final customer cars we will see shortly launched to the public. To get the type of down-force you refer to I would have thought perhaps front dive planes would be required? the 991 GT3RS is clearly wider at the front and rear axles than the 991 GT3 with conforming bodywork. The wheels on the model are clearly staggered sizes and again confirm what I have been told which is that the wheel design is identical in style to the existing GT3.
I think downforce and grip will definitely be increased significantly. It will be fun to finally find out!
I think downforce and grip will definitely be increased significantly. It will be fun to finally find out!
#1183
I'm fairly sure the model is accurate.
#1184
Load ratings were increased on prior RS per Michelin (https://www.michelinapex.com/message...email.thread):
997.2 GT3 F: 91 R:102
997.2 RS F: 93 R: 105
997.2 GT3 F: 91 R:102
997.2 RS F: 93 R: 105
When you look at the OEM fitment Pilot Sport Cup N spec that was specifically developed for 997, you get much lower load ratings:
997.2 GT3 F: 87 R:102
997.2 RS F: 89 R:101
At least according to Tire Rack. Where the PSC2s for the 918 and GT3 RS look OEM developed for those specific models, as is normally the case.
As for bricks and birds, I haven't done much work with either so I can't speak to the comp. My point on the 911 shape vs clean sheet is that the basic 911 shape of downward sloping tail - still present today, albeit highly massaged and modified - is not inherently good at generating downforce.
So the visual cues have largely been maintained, but the lift from the sloping tail has virtually, though not entirely, been eliminated through evolutionary design addressing this area.
The biggest aero drawback I see for the 911 is the underbody- the motor is right where you'd really like to put a diffuser/ tunnels.
#1185
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The original 1966 911 had a drag coefficient of around .38 to .39, and that's including its skinny little tires. A modern normal 991 is quoted as .27-.29 for the normal model depending on test. Airflow now remains attached over the back, and not only has downward slope on the tail been reduced by about 10 degrees, from 28 to 18, but with the standard spoiler the angle of the airflow is actually reduced further to something less than 12 degrees.
So the visual cues have largely been maintained, but the lift from the sloping tail has virtually, though not entirely, been eliminated through evolutionary design addressing this area.
So the visual cues have largely been maintained, but the lift from the sloping tail has virtually, though not entirely, been eliminated through evolutionary design addressing this area.