Tyre Model - does diameter change with wear?

Discussion in 'Knowledge Base' started by Reto König, Jul 8, 2020.

  1. Reto König

    Reto König New Member

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    As title says... ;)
    Search function didn't help.

    Last night we were having a small NSU TTS race at Knutsdorp, and some of us were experiencing reaching the revlimiter towards the end of the 1h race which didn't happen in practice or early in the race at different sections.

    So we're discussing why this happens and I'd appreciate if someone could clarify. o
    To me the most logical reason would be that the tire model includes a decrease of tire diameter with wear, so the overall "gearing" gets shorter during the race.

    Am I right?
     
  2. Vale

    Vale Well-Known Member

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    My guess is the car weight would go down due to less fuel therefore better acceleration.
     
  3. Reto König

    Reto König New Member

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    I don't think so Vale, because we ran with only little fuel in practice and it did not happen then
     
  4. Arcson

    Arcson Well-Known Member

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    Maybe they were experiencing it being in a draft? Sorry for such a basic suspection, but its one of the possible options
     
  5. Reto König

    Reto König New Member

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    Definitely no reason to be sorry, many times the basic suspection is the right one but here for sure it is not or at least not the only one...
    Because it also hapoened with no other cars nearby!
     
  6. fischhaltefolie

    fischhaltefolie Well-Known Member

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    Did speed decrease at same rev level?
     
  7. Reto König

    Reto König New Member

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    Not sure about that, didn't pay attention during the race and none of us had telemetry running unfortunately!
     
  8. BeefMcQueen

    BeefMcQueen Well-Known Member Beta tester

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    The speed your speedometer shows you will remain the same for a given amount of revelations your wheels are doing. It does not show you your ''real" velocity relative to your world. Revelations are measured using ABS sensors or Hall-sensors at the differential for example. So if you hit the limiter the Speedo will show the exact same speed no matter if your tyres are worn down or fresh. The only difference would be that your real speed would be maybe 1% slower due to the shorter circumference and resulting decreased distance the wheel travels per revolution.
    (A 63cm diameter wheel with a 2.5mm wear (5mm diameter decrease) would reduce the circumference from 197.92 cm to 196.35cm that's roughly 1%)
    But to be honest, I can not answer the initial question about how this is modelled in the game. Will ask the devs about that.

    Oli
     
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    Last edited: Jul 9, 2020
  9. Reto König

    Reto König New Member

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    Thanks for the initial response, hopefully the devs will let us know...
     
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  10. Alex Hodgkinson

    Alex Hodgkinson KW Studios Developer

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    You are correct!
     
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  11. fischhaltefolie

    fischhaltefolie Well-Known Member

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    I had this in mind, when I asked.
    My winter-tyres have slightly smaller diameter and my daily way to work with them is a bit longer than with summertyres.
    It was just an attempt.
     
  12. Alex Hodgkinson

    Alex Hodgkinson KW Studios Developer

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    Also the speedometer in game is effectively "gps based" so shows velocity which is unrelated to wheel speed. Try locking up all wheels at speed and you'll see the indicated speed doesn't drop to zero.
     
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  13. Zziggy

    Zziggy Well-Known Member

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    Still mathematically it is only a small difference: if we say that in a short race you will lose 2mm of rubber, this is only 4mm of a tyre diameter of 536mm so less than 1 percent (0,7%). So the topspeed will rise only form 160 to 161 and I doubt if this is discernable.
     
  14. Reto König

    Reto König New Member

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    @Zziggy Not sure if you simply mistyped, but topspeed will obviously decrease once tyres become smaller.
    Seems like a very small difference, but with the NSU it was noted by 5 drivers or so towards the end of the 1h race. Tyres where in the range of 5-20% depending on the driver.
    Quite possible it's more noticable with such a low power car as the NSU, compared to the more regular racecars.

    @Alex Hodgkinson thanks for looking into this and answering in detail.
     
  15. Zziggy

    Zziggy Well-Known Member

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    You are right I followed the wrong path of logic!:( A 0,7% increase in revs would then be from 7000 to 7050, not much either but maybe just enough to hit the limiter.
     
  16. fischhaltefolie

    fischhaltefolie Well-Known Member

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    You see when I wrote this?:mad::confused: 04:52 am!
    Don't need no smartypants around here to teach me better!;):p

    If it's enough, this little bathtub scratches the limiter, it might be seen on speedo, too.
     
  17. Alex Hodgkinson

    Alex Hodgkinson KW Studios Developer

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    The rear tyre radius is 0.264m, which gives us a rolling circumference of 1.658m when new.
    Currently in game 20% wear gives a rolling circumference of 1.627m, which is a decrease of near enough 2%.
    I think that probably confirms the OP.
     
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    Last edited: Jul 9, 2020
  18. Maskerader

    Maskerader Well-Known Member

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    BTW, no need to convert diameter to circumference to calculate the percentage. It's all linear relationship between diameter, circumference, speed and revolutions per second (although this one is inverse). X percent change in one variable means X percent change in all the others.
     
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  19. Lixma

    Lixma Honorary QA

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    I encountered this phenomenon tonight during a 30min race at Spa.

    Early on in the race at the end of Kemmel straight I was tickling 280kp/h (no DRS etc), but during the last few laps I could barely hit 270kp/h (tires averaging appx 20%).
     
  20. Skidmark

    Skidmark Well-Known Member

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    This is a really interesting discussion. Had no idea that this would occur. Gotta love physics. Thanks everyone.