Burnout physics/Exploits

Discussion in 'General Discussion' started by Nieubermesch, Jul 16, 2021.

  1. mantasisg

    mantasisg Registered

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    Interesting thing about oscillations when doing burnouts that are seen in those telemetry outputs. I wonder what it is. Could be the way they generate grip doing wheelspin. Tires might have this pattern of slip-grip-slip-grip, and it could transfer oscillation into chassis I guess... Well maybe, it would probably be stronger with drivetrain wobble if it was there in rF2 (although car like that probably wouldn't have that happening).



    I think it is same as this wrinkle effect as seen in this dragster clip, just of course on dragster it is way bigger:


    I also suggest that it is not that hopping somehow gives car better traction. It is other way around better traction gives car hopping. Each of that wrinkle is a sign that tire is gripped and locked to the surface, then it slips through while transferring torque to the car to make it move forward, meanwhile it grips again in same way. It is actually happening all the time in driven wheels when car is being propelled forward by them, it just happens very fast and with a lot more tiny slips, and as slip ratio grows slipping area of contact patch grows, till it is 100% slip ratio and whole contact patch slips. I am not exactly sure it is exactly how it happens, but it is somewhere there in that direction. It is confusing to me when it would be situation when tire slip is constant, and when tire slip oscillates with gripping back and forth. I would never believe it could possibly get anything else but constant sliding when car is almost stationary and rear wheels spin at roughly 110km/h, but you never know. It is weird.

    @Nieubermesch That competition BMW M2 has way too little sharpness in how those kind of tires perform in my opinion. IMO it would be great car to experiment with new tire stuff that S397 brought recently, It is also mostly mechanical grip car, it seems, so tire would be felt more.
     
  2. green serpent

    green serpent Registered

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    I thought of a different way to approach this which is probably fraught with just as many pit falls and variables to perhaps make the results not very accurate and thus ultimately pointless. But it could be fun.

    Using the NSX-R and/or various other cars with well established acceleration figures, simply do 0-100km/h runs and see if the numbers match. My bet is that even on a green track and with other various disadvantages, the sim car will be slightly faster.

    Obviously, the drivetrain will have to be treated as if it were real (no instant shifting) and obviously the aerodynamics will play into it (from memory I think something about the NSX aero was wrong). Anyway, dosn't need to be the NSX, just has to be something with lots of existing data. Like this (3.0lt NSX-R):

    Est. 0 - 40 kph 1.5 s
    Est. 0 - 50 kph 1.9 s
    Est. 0 - 60 kph 2.3 s
    Est. 0 - 70 kph 2.8 s
    Est. 0 - 80 kph 3.7 s
    Est. 0 - 90 kph 4.3 s
    0 - 100 kph 5.4s

    Even if we just kept it in first gear to remove the variable of shifting and gathered data for example zero to 50kph of various sim cars it could work. My prediction is that sim will be faster than RL due to possible higher longitudinal traction. If track is green, tire pressures are set high, and even then each car performs better than real life, that could be useful.

    I guess though it is just as much as a test on the clutch and drivetrain as it would be the tire. And seeing as the clutch isn't properly simulated that would throw even more doubt in the mix as to the accuracy of the results. Not to mention variability in track surface, atmospheric conditions etc.

    I would do this myself, but I have yet to figure out the whole Motec thing, one of these days!


    Also, braking might be a good one too, as it removes to an extent the variable of the drivetrain (provided the real world driver wasn't downshifing during threshold braking).

    Est. 60 kph - 0 16 m (52 ft)
    Est. 100 kph - 0 39 m (128 ft)
    Est. 120 kph - 0 54 m (176 ft)
    Est. 130 kph - 0 64 m (208 ft)
    Est. 140 kph - 0 73 m (240 ft)
    Est. 160 kph - 0 97 m (318 ft)
    Est. 180 kph - 0 119 m (390 ft)
    Est. 190 kph - 0 134 m (439 ft)
    Est. 200 kph - 0 149 m (489 ft)
     
  3. Lazza

    Lazza Registered

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    Apart from the multitude of extra variables here (including vehicle mass, actual output horsepower, track friction) I think this may not be very illuminating - an ideal straight run will have just the right amount of longitudinal slip. This will produce peak grip.

    I don't think there's any suggestion, or reason to think, the sliding friction in rF2 is exceeding the peak grip. So if there is an issue with fast sliding grip, it won't show in a straight line test where fastest time is the goal.
     
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  4. green serpent

    green serpent Registered

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    Having both had road tires on my car and semi slicks, the semi slicks definitely "bagged up" when I tried to do a burnout (I say try because the grip was massive!), compared to the road tires which did not bagg up and were very easy to get spinning, even with like 180hp max with an LSD.

    I can only think that once the tires are fully spinning the grip/no grip/grip behaviour would stop and thus the ocillations would stop.

    Like with many other things, the more granular you try and become with something, it's like the more uncertain things become as so many variables reveal themselves. Without the ability to do an actual objective test with all the variables understood, I guess at just some point you have to err towards trusting the experts, and that this is just some kind of anomalous behaviour rather than some fundamental flaw.

    In saying that, I find it interesting, and I just really want to know the answer out of curiosity.
     
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