Possible bugs in TGM tyre model or TGM/ttool documentation

Discussion in 'Bug Reports' started by Knut Omdal Tveito, Sep 11, 2014.

  1. Knut Omdal Tveito

    Knut Omdal Tveito Registered

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    WLF transform calculation
    In the TGM Quickstart guide the following is presented:
    log10(aT) = -8.86 ((Tq - Tg - 50) / (51.5 + Tq -Tg))
    Sliding friction coefficient is given as a function of:
    log10(aT*V) = log10(aT) + log10(V) ------[Eq.1]

    However from the ttool and the telemetry I have found the following to be the implemented:
    Sliding friction coefficient is given as a function of:
    LOG10( EXP( log10(aT)[Eq.1] + LN(V) ) )=( log10(aT)[Eq.1] )/LN(10) + log10(V) -----[Eq.2]

    It seems like either the TGM Quickstart guide does not include this detail of logarithm base or the tyre model itself has a bug. Would be great if ISI could clarify as it has a significant impact on peak temperatures etc...


    Sliding friction scaling (adhesion/micro/macro)
    In the TGM Quickstart guide these curves are presented as friction as a function of log10(aT*V). Based on curves like this in the literature I would assume the total is:
    mu_total ="SlidingBaseCoefficient" * MAX( mu_adhesion , mu_micro , mu_macro )

    But from the telemetry I have found the following:
    mu_total ="SlidingBaseCoefficient" * MAX( 0.25*mu_adhesion , 0.5*mu_micro , 0.25*mu_macro )

    These multiplication factors are not obvious to me, and when I enter the friction data in the TGM file I expected the exact numbers to be used and not scaled like this. Again, I'm not sure if it's a bug, but it would be nice if ISI could clarify the Quickstart guide so that people don't make the same mistake as me.

    I hope You find the time to answer.


    Thanks in advance!
    Knut
     
  2. Terence Groening

    Terence Groening Member

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    I don't have time to look at the first one right now, but I know the second answer off the top of my head: those ratios comes from the "Roughness" profile for the terrain. Note that the SkipBarber tire files have a comment mentioning this. Ideally, one could use the "Roughness" profiles to describe the different types of aggregate used in asphalt, in addition to differentiating concrete surfaces.
     
  3. Terence Groening

    Terence Groening Member

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    A quick idea: I think those Log10's are supposed to be natural logs in the documentation, but again I don't have time to go through all that right now.
     
  4. Knut Omdal Tveito

    Knut Omdal Tveito Registered

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    Thanks for the reply, much appreciated! I will look into the terrain.

    For the logarithm, I have to point out that aT and V have a different logarithm base, and that sounds like a bug to me as they usually appear as a product in the logarithm expression. As a result the relative influence of temperature and sliding velocity is not in accordance with litterature. The way it is now the problem can be overcome by changing C1 iun WLF (-8.86).
     
  5. Dhurara

    Dhurara Registered

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    This thread is very instructive for a modder who is interested in the tyre model of rFactor 2 :cool:

    Unfortunately I don't have enough skill and knowledge to validate the model.
    But the discussion between knowledgeable persons will offer us valuable insight into the model :)
     
  6. Raintyre

    Raintyre Registered

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    I also would like to ask about WLF equation. From tyre documentation WLF equation would be:

    log10(aT) = - 8.86 ((Tq - Tg - C1) / (C2 + Tq -Tg))


    However, in most of sources i found WLF equation form is:

    log10(aT) = - K * (T - Tg) / (C2 + T - Tg)


    So, is documentation right? Can you confirm what is the exact equation to apply for 'WLFParameters' line?

    Thanks !!
     

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