Andi76 wrote: ↑09 Mar 2023, 21:32
ing. wrote: ↑08 Mar 2023, 19:30
Are you saying that the rubber compound behaves like metal—applied loads to work harden the compound and heating to temper the compound? I’d be surprised if that’s the case but would be interesting to discover more. Specifically, how do you think this hardening and softening affect thermal degradation and grip?
I made a post last season about contact frequencies and temperatures that hopefully can answear your question:
The mechanism determining a tires actual compound softness when its in action is complex and is only partly to do with the base softness from its ingredients. Tire temperature and the contact frequency(rubbers frequency of contact with the track) are the two other main determiants. These work in opposite directions. As temperature rises the compound becomes softer(you can see this with plasticine). As contact frequencies rises the compound becomes harder. Getting to the point at which the tire achieves its ideal state (vitreous transition) is therefore a delicate balancing act. The higher the contact frequency, the more temperature you need to compensate in order to keep the tire at its intended compound softness. Contact frequency is about how the loads react uppon the rubber. Because rubber is s viscoelastic material, the way it reacts to loads is not consistent. Up to a point the rubber will accept the incoming energy and react against it, trying to spring back in the opposite direction to the load and thereby creating grip. Beyond that point the rubber cannot regain shape quickly enough to absorb the next input of load. This has the effect of stiffening and hardening the compound, breaking the process down and causing the tire to slide. When the compound is overwhelmed in this way its better to get to a harder base compound that will better stand up to the energy fed into it.
This is also the reason why F1 teams usually say - our car works better with the harder tire. Because it is then actually so that when the contact frequencies for the softer tire are too high, the harder tire is comparatively softer for them.
Many people completely underestimate the complexity of this issue and many things play into it. In today's cars, which you want to drive as low as possible on a permanent basis, especially the stiffness of the suspension.
As for hardening and softening in general - you have to know that racing tires are not fully cured. They would otherwise be too hard to have the corresponding performance. In use, the rubber sees mechanical working and time at elevated temperatures very similar to the processes it saw as it was manufactured, in different cycles. What ultimately happens here is nothing other than that the vulcanization process of the tire continues, he gets more cured and becomes harder. This is why the lap times of cars with high degradation also become worse, because the tire practically becomes harder after going through a heat cycle (high temperature in corner, lower temperature on the straight, for example). The so-called ideal operating temperature of a tire is also the temperature at which it does not cure or hardly cures, which in turn is also related to the temperatures during its manufacture and its compound. The described mechanism of hardening(contact frequencies too high) and softening(temperature rise) is also naturally subject to this. As soon as the temperature rises above a certain point (e.g. in a curve) and cools down again (e.g. on a straight line), the tire will become somewhat harder. Working with "more temperature" to make the tire softer only works if it is within the working window of the tire, which is usually 20 to 30 degrees. At higher temperatures, the tire will become harder in this heat cycle and that is ultimately what tire degradation is.
From that reason i m advocating that active suspension could level playing field even. Because all that knowledge big teams gathered in those tire wars, Pirelli blow-ups with those passive systems are invaluable. Some might even argue most important part of car design.
