michl420 wrote: ↑16 Feb 2023, 19:09
I have two specific questions.
For mercedes in special, there is a talk to lower the rear in straight line. For me this means automatic to rise the rear in corners. Why would someone rise the floor in a corner where i need the downforce from it?
The 2022 Red Bull front suspension setting with the lowered rear arms is discribted as "pro-dive".
Same question as above. Why run so high that there is a need to lower the front even more (and on top even more than the front dives in anyway under braking)?
From my understanding, this ground effect cars need to be as low as possible anytime and particularly in a corner, where the downforce is most important.
This "pro-dive" theory was something Scarbs brought up in early 2022 I believe. But he got away from it relatively quickly and generally such a lower positioning of the rear arm is an "anti-dive" geometry. Pro-dive would also make little sense, because generally with these cars you want them as close to the ground as possible. If you want the car as close to the ground as possible you have to increase the stiffness of the suspension (I suspect that inadequate stiffness is a problem with some teams, hence the high degradation), which is in contrast to wanting to save weight at all costs. On the other hand, a stiffer suspension also increases the contact frequency.
Contact frequency. Contact frequency is how the loads react upon the rubber. Because rubber is a viscoelastic material, the way it reacts to loads is not consistent. Up to a point, the rubber will accept the incoming load and react against it, trying to spring back to its original shape and produce grip. Beyond that point, the rubber can no longer regain shape quickly enough to absorb the next incoming load. This has the effect of hardening and stiffening the compound, which breaks this process and causes the tire to slide. Higher temperatures have the effect of softening the compound. Contact frequency and tire temperature therefore act in different directions. When the temperature increases the compound becomes harder, when the contact frequency increases the compound becomes harder. To bring this into the window where the tire has its ideal condition is therefore a delicate balancing act. The higher the contact frequency, the more temperature is needed to keep the tire at its intended compound softness. So you need the right stiffness of the suspension which has to be in line with how much energy you put into the tire.
But if you want to keep the car lower, you have to increase the stiffness of the suspension, which of course makes this an extremely difficult thing to do, which many people don't understand and think there's some trick to the Red Bull's suspension. A pullrod suspension is a second lever system whose characteristics are softer than those of a pullrod suspension. A softer suspension reduces the contact frequencies and therefore simplifies the problems and difficulties described, which is probably the main reason why Red Bull opted for this type of suspension.
But anyway - when the front lowers at speeds the characteristics of the second class-lever system stiffens as it is a rising spring rate. This supports the platform as are loads are introduced to the cars inputs, so "Pro-Dive" makes no sense. The Multilink Arrangement sees the trailing edge wishbone swept back and intersecting with the chassis significantly further back down the front one. Because of the sensitivity of the cars and its aerodynamics you want to keep the platform as stable as possible at constantly low ride heights. So this design is clearly "Anti-Dive", "Pro-Dive" makes no sense, especially with front-wings much less effective.
Anti-Dive Geometry diverts the forces transmitted under high aerodynamic and breaking loads away from the springs and dampers through the suspension links to minimise disruption to ride height. This limits the rear ride height increase and the loss of downforce it entails under breaking, what again shows why "Pro-Dive" just makes no sense.
Pullrod is slightly heavier than pushrod, and the RB18 and RB19 have a pushrod rear suspension. This is to provide stiffer and lighther mechanical installation to preserve platform control needed to support the ground effect aerodynamic regime. Pushrod also allows tighter packaging of the suspension, helping it free from encroaching on the diffuser area, which aids the efficiency of the ground effect floor and beamwing interaction. The long rear suspension travel allowed it to run low at high speeds, reducing drag. Despite having a greater static ride height (RB18 - RB19 has a different philosophy in that regard), combined with a relatively soft spring rate allowed the car to settle low in such a way as to enable hight straight line speed compared to the competition.
I'm sorry, but the "pro-dive" theory makes no sense, whereas the anti-dive geometry makes sense in every way and also explains Red Bull's choice of concepts. This suspension is clearly an "anti-dive" geometry. And especially in connection with the tires, it explains some of the advantages that the Red Bull has, because the design was precisely aimed at optimizing and exploiting the advantages of these concepts.
Of course, one has to mention that one could also analyze the design decisions of others regarding the suspension, because here too there are certain advantages that can be maximized and exploited, as for example a pullrod rear suspension allows for comparatively better traction at times of very stiff suspensions thanks to its inherently softer characteristics, but ultimately it was about Red Bull's front-suspension and "Pro-Dive", which just doesn't make sense in terms of the requirements.