Burnout physics/Exploits

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

  1. green serpent

    green serpent Registered

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    I actually made a mistake in my original post, 90s tires only had 10% wear, so these tires seemed to come very close to "passing" the test.
    Back when I was a weathly man and could afford iR, I would do line-lockers at the end of pit lane in the Mx-5. So definitely in this respect iR is "correct", but again none of this is to say that anything here is fake. I found another video with a Cobra pushing the front end at various times in this rather ugly burn out session (at the very beggining and at 40 sec). The surface looks pretty rubbered in.



    Here is a clip though of a Cobra doing a text book perfect one with no front tire push at all (40 sec again).
     
  2. Sim_Player

    Sim_Player Registered

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    that 2nd video burnout was smooth af.
     
  3. Sim_Player

    Sim_Player Registered

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    Lol try FISI ->
    fisi 1.PNG
     
  4. Nieubermesch

    Nieubermesch Registered

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  5. Nieubermesch

    Nieubermesch Registered

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    Well, seems that under the right conditions it's realistic behavior then. Probably all the things like rubber and no tarmac heating are the culprit :).

    Still, has anyone seen the video with the BMW M2 CS lap? It's so strange seeing record times being achieved like that!
     
  6. green serpent

    green serpent Registered

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    I think as @Sim_Player mentioned, the bobbying around and vibrating that the cars are doing is probably not helping the situation either.

    The times he is getting (while very fast, and maybe too fast), are generally not the fastest lap times. Not actually "records or world beating" as far as I have seen. Henri is fast, but there are faster sim racers who are less slidey. So at best, sliding does not lose much (if any) time, but probably not gaining much time. I wonder if there are any other videos from others sim racers that are really abusing the car and getting the fastest time? From what I have seen the really fast guys like Nuno Pinto and Risto Kappet etc are not overly slidey (from what I have seen).

    My own personal experience with many stints in the past goes something like this:

    Try to drive using real world techniques, trying very hard to be smooth and flowing perfectly through corners as if I were driving the car IRL > get smashed by the AI, so decide to be way more aggressive and abuse the living shite out of the car > get a hugely faster lap time straight away, start thinking rF2 is fake > keep trying to get faster > eventually find that being very aggressive AND very smooth/not too slidy is the fastest.

    Basically, although sliding and mashing on the throttle will be much faster than a timid and overly cautious yet technically perfect style, ultimately being less slidy, very smooth but still massively aggressive has always been faster for me. And I've tested this out quite a lot, and each time that is the result. Do I think sliding should be punished more, yeah probably, but proper driving style is still faster imo.

    Edit: I still do feel though that something is NQR (in a very general and subjective way, i.e I have no actual evidence to back this and I'm not saying that it is fact). After watching dozens of hours of rF2 on board, the front end of the car seems to move in a very non linear way. The trajectory of the car is very darty and it lurches around too much imo compared to RL. If you drive down a straight in rF2 and go hard right to hard left in steering, you will notice a very non linear kind of "lurching" that the car does. For example the car will turn, then settle, turn, then settle etc. Could be totally realistic, but compared to RL onboard the trajectory of the car seems too hectic and not moving in smooth flowing linear arcs. You will notice A LOT in rF2 on boards little "gathering up" steering motion at the exit of corners, again and again and again. The car may not even be sliding and still these little gather up moments of steering input at the exits of corners. Just seems like the car is a bit floppy on it's chassis or something. This could or could not be related to the whole topic of this thread, IDK.
     
    Last edited: Jul 18, 2021
  7. Sim_Player

    Sim_Player Registered

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    @green serpent I think oscillating may explain it on bmw case BUT after doing same test on FISI i got no oscillation for good time period...there I still got same situation i.e front wheels completely locked and car is moving forward (quite a bit fast in FISI case)
    So overall i'm not too sure that this engine cut off is causing problems or not...probably entirely dependent on how tyres are made(what parameters they have etc).
    So, the question is that whether this is a new issue that even latest tyres (with better data and stuff )are not immune to ? i hope not.
     
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  8. Nieubermesch

    Nieubermesch Registered

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    I commented under his video asking and his times are not the world record but close by ms's, so it kinda is fast, maybe the fastest. I mean, I had already tried with a Porsche GTE to drive more by sliding and abusing slip angles and setups and by just the first time doing it, I was beating my lap times at Spa and I'm a somewhat decent driver to be honest, at least to not just surpass those clean laps with just a crazy driving way.
     
  9. 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.
     
  10. 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)
     
  11. 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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  12. 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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