992 Wing Riser FEA

"Are they strong enough?"

"Are they safe?"

"Where have these wing risers been all my life?" 

All logical questions one might ask when considering our modular 992 wing riser setup. In order to address any concerns about the strength of our modular wing risers, we've employed industry-standard FEA (Finite Element Analysis) techniques to characterize the behavior of our wing risers under extreme loading conditions.

To set up the test, it's first necessary to know the level of downforce produced by the 992 GT3's wing. Reports are somewhat mixed online, though the consensus seems to be that the whole car, with its rear wing set to maximum angle-of-attack, produces about 385kg of downforce. While the body of the car, front aero elements, etc. also contribute to this total, for the sake of our testing, we assumed the worst case- the full 385kg applied at the rear wing.

It's also important to note that RSNV wing risers are machined from billet 6061-T6 aluminum, as opposed to the stock risers' cast aluminum construction, bringing us nicely on to the concept of yield stress. Put simply, it's the load at which a given metal is expected to bend beyond repair.

In our FEA, the stress result is reported as "Von Mises Stress". Von Mises stress is a way to predict when a material will start to deform or fail under complex loading conditions. Imagine a piece of material being stretched, squished, and twisted in different directions all at once. Instead of looking at each of these forces separately, Von Mises Stress combines them into a single number that tells us how close the material is to breaking, or permanently bending.

If the von Mises stress is lower than the material's yield stress, it's typically safe; if it's higher, the material could be at risk of bending or breaking. Below is a table of yield stresses for some common metals.



In order to run the analysis, the geometry of the wing riser assembly had to be slightly simplified, as complex geometries require exponentially more time to apply the required "mesh" to the body, and to perform the FEA calculations. Some of the more complex features of the base were smoothed out, and the screws connecting the upper and lower riser were modeled as solid cylinders bridging the gap between the two parts.

Given the known downforce figure of 385kg, we can assume a load of 385/4, or 96.25kg at each of the mounting bolts. The three mounting points in the lower riser (secured to the chassis with hefty 13mm bolts) are modeled as fixed points which cannot move. After applying a mesh to this geometry, the resulting Von Mises Stress and deflection in the part can be modeled.


At these extreme loading conditions, the highest Von Mises Stress experienced at any point in the aluminum structure of the riser was about 80 MPa- approximately 30% of the stress required for 6061-T6 aluminum to yield. This can also be expressed as a "safety factor", as commonly used in engineering analyses. It's calculated by dividing the yield stress by the actual stress experienced by the part- in this case, 275/80, or a safety factor of 3.4. This goes well beyond the typical safety factor of 2-3 used widely in the automotive industry!

Digging deeper into the results, we do see that there's a tiny sliver of the assembly experiencing Von Mises Stress as high as 190 MPa. As expected, this is localized to one of the six bolted joints connecting the upper and lower riser. Fortunately, the supplied bolts are constructed from A2-70 Stainless Steel, with a yield stress of 450 MPa, and this load is spread across six bolts.

It's also interesting to see that at this absolute maximum loading condition, the peak deflection in the riser is only about 1.3mm at its rear. But given that the riser is rigidly bolted to the wing, in the real world, the actual deflection would likely be even less.

And if all the computer-aided analysis in the world isn't enough to convince you, our prototype 992 wing risers have already been tested by early adopters at speeds up to 150mph on the street and track. We're 100% confident that these risers are strong enough to handle any abuse you can throw at them- even maximum attack on the track.