Discussion
Taffy66 said:
.As Isaldiri points out the R's problem with instability arose from the front splitter reducing lift at the front which was out of kilter with the rear, hence why Porsche added a Gurney lip on the Touring's rear lid.
But it's not unstable which was my earlier point. SportAuto I believe found it to be +10kg front / -10kg rear at 200km/h. Which essentially is negligible. Downforce is usually targeted at being slightly rear biased as the effect is obviously greater the higher the speed and no one really wants to deal with high speed oversteer but that isn't the case with the R as the amounts are just too small. The gurney flap on the touring has cleaned up the overall airflow to produce a very small amount of df on the touring but it still overall is a bloody small amount in the grand scheme of things, especially in a 1500kg car.
SportAuto test of the 991.2 GT3 (with wing) reported (English courtesy Chrome translate)
"Due to the new aerodynamics of the 991.2 GT3 has more downforce at the rear than the 991 GT3. In the delivery status (rear wing position 5 degrees), the output is 19 at the front and 42 kg at the rear.
In the supertest was driven with the performance position of the rear wing (9 degrees). Result: more downforce.
Front axle at 200 km / h: 16 kg downforce
Rear axle at 200 km / h: 53 kg downforce"
The tests are run in a Mercedes moving floor wind tunnel at 200 kph
"Due to the new aerodynamics of the 991.2 GT3 has more downforce at the rear than the 991 GT3. In the delivery status (rear wing position 5 degrees), the output is 19 at the front and 42 kg at the rear.
In the supertest was driven with the performance position of the rear wing (9 degrees). Result: more downforce.
Front axle at 200 km / h: 16 kg downforce
Rear axle at 200 km / h: 53 kg downforce"
The tests are run in a Mercedes moving floor wind tunnel at 200 kph
gtsralph said:
Yellow491 said:
But look at the rear window.
we also ran more rake for a high speed track,think of the wedge effect to let air out faster underneath at the back than how it is coming in at the front,if you loose the wedge effect by rear compression you start to loose the effect and create lift the faster you go.
I wonder how many have experienced true down force,its amazing when working and can be a nightmare when it disapears with out notice!
isaldiri said:
Very much so. Downforce acts as a function of the weight of the car as well so for heavy road cars the effect of downforce on cornering speeds really isn't as much as marketing would like one to believe.
Fair enough but say 150kg of downforce is not like adding 150kg of weight to a car to benefit cornering at high speed..Downforce is merely an invisible force not subject to the laws of centripetal force..The best sports cars are always the lightest in terms of cornering irrespective of downforce, as adding weight to the car increases centripetal force, totally negating any perceived benefits from invisible downforce.
Taffy66 said:
Fair enough but say 150kg of downforce is not like adding 150kg of weight to a car to benefit cornering at high speed..Downforce is merely an invisible force not subject to the laws of centripetal force..
The best sports cars are always the lightest in terms of cornering irrespective of downforce, as adding weight to the car increases centripetal force, totally negating any perceived benefits from invisible downforce.
I rely on gravity :-) again in the wet light cars are pretty poor. The best sports cars are always the lightest in terms of cornering irrespective of downforce, as adding weight to the car increases centripetal force, totally negating any perceived benefits from invisible downforce.
Taffy66 said:
Fair enough but say 150kg of downforce is not like adding 150kg of weight to a car to benefit cornering at high speed..Downforce is merely an invisible force not subject to the laws of centripetal force..
Obviously adding 150kg of downforce isn't the same as adding 150kg of weight to a car. That's about as obvious as lift being well lift and downforce being negative lift I'd have thought.Taffy66 said:
The best sports cars are always the lightest in terms of cornering irrespective of downforce, as adding weight to the car increases centripetal force, totally negating any perceived benefits from invisible downforce.
That depends very much on the amounts of downforce involved relative to the weight of the car. A radical that is considerably heavier than a caterham might very well have greater cornering capability because of the downforce it generates.There is most certainly an aero effect above 120mph the characteristics of my Carrera 3 changed radically, and frighteningly, with the front "lifting" and the streering going decidedly light. It appears to me that most of the rear aero is to balance the front aero and to keep the car as neutral and consistent through its speed range as possible.
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