Tire temperature model

Discussion in 'Car Modding' started by Yoann56, Jul 24, 2020.

  1. Yoann56

    Yoann56 Registered

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    I don't have the same evolution of the tires temperature compared to the reality and I need your help.

    In reality, I adjusted the tire pressure at 1.3bars (tire at ambiant temperature 25°C). And after 3 laps, we checked the pressure and we are between 1.9 and 2.0bars. Michelin told us that we are at the optimal pressure and don't pass over 2.0bars otherwise the performance will drop.

    But in rF2, I need to put 1.7bars in the garage to obtain between 1.9 and 2.0bars after 3 laps. And when I put 1.3bars in the garage, I've 1.6bars after 3 laps.

    So how I can increase the speed of temperature rise ? And keep the optimal pressure at 1.9 and 2.0bars after 3 laps.

    Thanks
     
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  2. Yoann56

    Yoann56 Registered

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    Start at 1.3bars
    upload_2020-7-24_22-21-13.png

    Start at 1.7bars
    upload_2020-7-24_22-22-21.png
     
  3. mantasisg

    mantasisg Registered

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    You can try increasing thermal depth and decreasing ground conductance in [realtime] section of tgm file, I am not completely sure but I suppose it would influence inner temperatures too and eventually heat and expand air in the tire.

    There are also parameters like:
    InternalGasSpecificHeatAtConstantVolume
    DampingHeatEnergy
    InternalGasHeatTransfer
    ExternalGasHeatTransfer

    But I am not used to those.

    Anyway... in rF2 optimum pressures seems to be the lowest pressures.
     
  4. Raintyre

    Raintyre Registered

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    >>>>So how I can increase the speed of temperature rise ? And keep the optimal pressure at 1.9 and 2.0bars after 3 laps.

    Typical RF2 tyres are very slow to stabilize pressures, you can drive for 7 or 10 laps until they reach maximum. Why? I don't know exactly. It's a result of many things. Is this realistic? I don't think so.
    The good new is that we still can change some thermodynamic properties to obtain something closer to the real thing.

    Normally, the tyres are accumulating heat slower because the overall "specific heat" is too high. Specific heat is like the inertia for temperature speed. That means the tyre accumulates heat slowly, due to damping heat energy introducing energy constantly and also cornering friction, of course. Internal conductivities are probably also slow and external refrigeration is not enough. Try setting a faster conductivity and lower specific heat rates for materials at each node.
    Those parameters can be changed without regeneration of the tyre.
    After that, depending on result, you can rebalance the model using the rest of thermodynamic parameters.

    Apart from those that Mantasisg said, don't forget this one, it can help a lot:
    DryTerrainEffect=( , , x) /// multiplier for cornering friction heating rate

    Also, conductivity and specific heat rates can be set for different temperatures. This means that you might be interested in applying a low specific heat when the tyre is cold (so that it heats up fast) and a high specific heat rate when the tyre is hot (so that it doesn't heat up so easily when it is already hot)

    TreadMaterial=(273.15, , , , , 850, 0.251) /// for 0ºC
    TreadMaterial=(373.15, , , , , 6750, 0.241) /// for 100ºC

    The goal is not to use realistic specific heat numbers, of course, this is not important at all, don't mind using unrealistic values ten millions bigger than realistic. The priority is achieving a realistic result.
    Realistic values that provide unrealistic results are useless. Perhaps we are allowed to use unrealistic values which lead to realistic results, instead.

    Remember that temperature behavior will also change handling, because tyre flexibility and grip properties also change fast depending on temperature ups and downs.


    Apart from that, the optimum pressure issue. This is very difficult to fix on RF2. Optimum pressures for grip are usually very low on RF2, probably because the model benefits too much the amount of contact patch surface, without having in account the issues that a low inflation induces. However, i don't know. The only thing sure it that optimum pressures are wrong, and that creates a chain of flaws (especially when we add them to other issues).
    For example, most of sim racers will use the minimum tyre pressures available if they want to be fast. No problem with roll resistance or tyre temperature, RF2 will not create enough of them at any pressure, no matter how low is it, but you will earn a lot of grip.
    The grip gain is so big that most of times it is not good to push the tyres to optimum temperatures, especially at endurance stints. Because if you push the tyres you will increase tyre temperature, and that is good if you are still under optimum tyre temperature, but that will also increase tyre pressure, and that is always bad. The more tyre pressure the more grip you lose, then it is better to keep tyres under their theorical optimum temperature. As a weird result we obtain that tyres are faster at temperatures below their true optimum temperatures.
    For example, if the theorical optimum temperature of a certain tyre is 100ºC, the 'true' optimum tyre temperature is 90ºC, because at 100ºC the higher pressure makes you lose a lot of grip..... and I don't think that's realistic.

    Well, i hope some day there is a revision or fix for those flaws...
     
    Last edited: Aug 8, 2020
    Yoann56 likes this.
  5. Lazza

    Lazza Registered

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    Not taking away at all from everything else you've said, but this last we can influence directly using the StaticCurve, right? So if in testing it seems beneficial to run the tyre cold (or 'cool'), because the low-pressure grip increase is larger than the low-temperature grip loss, you can reduce the static cold grip or move that temperature point closer to optimum and push the balance towards the optimum temp. Granted, it might be difficult to push it up 10-15 degrees without severely affecting the cold tyre grip, but at least we have parameters in there already.

    You could also increase the optimum temperature above the real optimum temperature, to offset the effect of low pressures.
     
  6. Yoann56

    Yoann56 Registered

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    I 've starded some tests and I will continue tomorrow.
    Many thanks for your help.
     
  7. David Wright

    David Wright Registered

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    Rising from 1.3 bar to shall we say 1.95 bar is quite a rise. A quick calculation suggests the air inside the tyre must have risen from 25 C to 110 C which seems very hot.

    One weakness of the rF2 tyre temperature model is (I believe) it doesn't simulate brake heat raising tyre pressure by heating the wheel rim which in turn heats the air inside the tyre. I don't think this necessarily will make the tyre pressure higher but will speed up the tyre reaching its equilibrium pressure and will result in more even pressures left to right.
     
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  8. Raintyre

    Raintyre Registered

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    Yes, probably both workarounds can help to compensate!
     

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