Technical Aero: 458 Italia vs Speciale

talk to the marketing committee

 

I'd give Ferrari credit, even if some of their styling details are marketing driven (eg. foglight on F12), they at least are functional.

I consider myself a function-over-form guy, while our 458 is a beautiful car, I really love it for the technical elements and how it drives. Candidly I find the 458VS to be a bit less pleasing to the eye but the technology works...same with the F12 aerobridge.

The moveable aero parts (458VS nose/diffuser, F12 brake ducts) are innovative, though pop- up wings have been around since the 1980's on 911's. I am interested in seeing how much one can feel the difference, especially the moveable diffuser (aka "upside down DRS").

 

Does anyone have any downforce numbers to compare?

 

Another forum member (Unotaz) posted this in May'13 which I thought was interesting and here is what he wrote:

This topic came across when I was reading the Sports Auto Supertest on the Ferrari 458. In Sports Auto Supertest, one of the testing criteria is the car's downforce (or lift). Sports Auto supertest uses Mercedes static wind tunnel to perform this test at 200km/h (or 124mph). In the case of the Ferrari 458, the downforce shown was shockingly low. It had 32kg of **gasp** LIFT in the front and 31kg of downforce in the rear. This result is very far off from Ferrari's own claim of 140kg of downforce at 200km/h and 360kg at 300km/h.

So I got curious and went onto Sport Auto's online database to look at the 12C and other cars: The Mclaren did ok and it showed that Mclaren does not lie when it comes to their factory numbers. Mclaren claims that the MP4-12C produces 120kg of downforce at 186mph. Sports Auto supertest showed a 2kg of downforce in the front and 62kg of downforce in the rear at 200km/h. Using Square's law, the 12C will produce 120kg of downforce at approximately 272.27km/h (or 170.17mph), based on Sports Auto's number at 200km/h.

Other notables were:
Lamborghini Aventador 28kg of lift (Front) and 73kg of downforce (Rear)
Porsche GT3RS (997 MK2) 2kg of lift (Front) and 10kg of downforce (Rear)
Mercedes SLS AMG 41kg of lift (Front) and 8kg of downforce (Rear)

After seeing these data, I guess producing any type of downforce over the front wheels is quite a challenge for auto makers!

 

The manufacturer shows us (maybe) just the positive downforce values.

I try to explain what I mean on the example of the F1 Ferrari F-1-2000.

This car reaches 100 percent (%) downforce with the following positive and negative downforce values:
Front wing 36,9% (downforce)
Rear wing 34,4% (downforce)
diffuser 41,3% (downforce)
front wheels -1,4% (up force)
rear wheels -2,3% (up force)
guide plate/winglets -0,8% (up force)
rest (car profile etc) -8% (up force)
-> Total downforce 100%

I guess it is clear that a car like a Ferrari 458 with his wing profile will produce a lot more negative downforce (up force) then a Formula 1 car.

The measured 32kg of **gasp** LIFT in the front and 31kg of downforce in the rear in your example is for sure the 100% downforce value. The numbers "140kg of downforce at 200km/h and 360kg at 300km/h" are maybe just the more impressive positive downforce values and the negative downforce values (up force) ​​are concealed in this marketing statement.

of course, these are only my 2 cents to this topic, I'm not sure if this is the practice...

 

These last posts are so amazingly interesting... Please keep on discussing!

 

+1

 

+1

 

Someone knows the correct answer for the 458 claimed downforces numbers vs the SportAutos test?
Like others members posted before,this thread is very interesting

 

Just explained different times.
Modern wind tunnel (Ferrari or Pininfarina) use G.E.S.S (Ground Effect Simulation System) allowing to put in rotation the wheels of the vehicle and to simulate the motion of the ground under the car.
Sport auto static tunnel does not.
Basically car with flat undertray tipically show a lift in the front because the air doesn't accelerate properly under the car.
The Sport Auto picture of the 458 in the static tunnel is emblematic.
Rear diffuser is not working at all
I don't know if ferrari numbers are a bit optmistic or not.
For the Ferrari Enzo I can say they were very optimistic

Luque
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I suspect Ferrari is working with calculated values (Computational Fluid Dynamics-System). They calculate an aerodynamic performance value of 1,09 about the parameters Cx 0,33 (drag coefficient in x-direction) and Cz 0,36 (lift coefficient in z-direction) which links to a total downforce amount of 140kg by 200km/h and 360 kg by Vmax.

There are no declarations about the assignment of the downforce between the front and the rear axle.

Important to know: more downforce would be no problem, but then suffers the aerodynamic efficiency (aerodynamic resistance) of the vehicle or the thermal property of the engine/drive unit.

Interesting such details like the front wings (or the new front system of the 458 Speciale): they don't optimize the downforce, they optimize the aerodynamics at high speed. By cars such as a 458, the driving stability and aerodynamic efficiency/resistance is more in focus as the pure downforce capabilities by a Formula 1 car.

Another interesting example are the movable flaps in the diffusor of the 458 Speciale: with these flaps the downforce can be canceled controlled, what leads to less downforce and a higher aerodynamic efficiency/resistance.

 

At the end of the day there is always the challenge of balancing down force with drag (resistance). Those who race cars know the challenge of making the car more stable when turning (for example) but at the same time not compromising straight line speed. The 458 and now the Speciale , continually work to minimize "resistance" primarily , but not exclusively depending upon enhanced aerodynamics. Best

 

Fascinating discussion. Just want to say thank you.

 

Well explained!

My considerations concerning stability at high speed: lets have a look to the two side wings from the Speciale, what kind of function do they have? There are basically two possibilities:
- more stability like the vertical tail of an airplane
- more efficient aerodynamic like the winglets of an airplane

I guess Ferrari is using both effects. Why?

The diffusor of the Speciale is bigger then the diffusor of the standard 458. That means the Speciale will produce more downforce, more downforce leads to higher resistance, higher resistance means less high speed. Thats bad!

Now lets have a look on the movable plates in the Speciale diffusor. Like written before, these moveable plates will interrupt controlled the downforce effect. I guess the system logic will produce controlled this effect if the Speciale is in a stable direction (straight ahead) to achieve a higher top speed (and of course to achieve also faster this high speed) and the system logic will not allow the downforce interrupt if the Speciale is in a curve or under braking.

To close the loop: the controlled interrupt of the downforce at the rear axel has the consequence that the stability of the car will a little bit suffer. To compensate this effect the Speciale has received these two beautiful wings!

And the reduction of disturbing air swirls is always appreciated.

Of course, these are only my 2 cents. How it really works only knows Ferrari

 

Admit I do not know much about the technical end, but at 140mph the 458 Spider is as steady as a rock. Better than the F355 GTS and 360 Spider.

 

I've heard it said that downforce aero aids are a free ride because though they may increase drag, who cares about top speeds that are not approachable anyway on almost all tracks. This is misleading because increased drag will reduce acceleration at all speeds, with its effect increasing rapidly with speed. So you have a tradeoff between downforce and acceleration whose optimum will depend on the track. And don't forget that downforce itself makes for increased rolling resistance, even if it is usually small compared to aero drag at high speeds. That is why the active devices that 'turn on' only when there is lateral accleration are so neat.

 

This has always been a topic of discussion regarding rear wing designs in our race cars - e.g. Curved vs straight wing, angle of attack, etc. in relation to downforce vs drag.

One question I had is if aero is so important with the 458S, why didn't they use a retractable rear wing and why not canards?

 

It's "Ferrari design philosophy" to don't use such aero appliances on a street car. You will find rear wings only on a F40 and F50, and there harmoniously integrated into the body design.

And imo they are right to do it on this way. Ferrari street cars are absolut stable enough also without such ironing-board's on the rear....

 

Coupe is good at 175 too!

 

Several modern Ferrari I have owned and driven always feel slightly nervous at extreme speeds above 180+ mph. I am comparing this experience objectively with my 12C.

Let's hope the improved active aerodynamics solutions will help stabilize and calm the latest super car with trick aero fins, vertical flaps, front glide vanes, turning vanes, dams/humps and active flap diffusers.

I am looking forward to spec mine ...

 

An "open" Mercedes S AMG 65 or a Porsche Panamera Turbo S is for sure also more stable above 180+ mph as a nervous racehorse.

It can be that the stability of a car is not only depending of the aerodynamic solutions...

 

Is that 458 too? I have driven mine at 175 and thought it felt great. Haven't driven 12 c that fast but my old gt3 rs did 200 and felt great par a few pesky vibrations!

 

Well, when I was driving at around 175 mph a few months ago, my 458 Spider did not feel totally at ease in the front. I still had lots of power left though ).

Without a rear wing, the degree of downforce you can provide with other design tricks will have its limits.

 

My Ford GT is the most stable car I have owned at speeds above 150. The aero on the GT is amazing. Next time you see a Ford GT look at the rear aero. Looks like an American Le Mans defuser.
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