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Thread: Potential bug with BMW 320 T

  1. #1
    WMD Member ironik's Avatar
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    Potential bug with BMW 320 T

    Hi,

    Some TGC guys and I have found something weird with the BMW 320 T @Silverstone GP.
    It's 100% reproducible.

    After some laps (7 or 8) the car starts to wandering right and left in straights.
    During the braking, the car is unstable. It's like the rear wheels are locking up and the car is waving. I have to countersteer while braking.
    It's not a proper tyres locking as I'm in fact applying less brakes than before the issue occured.
    The tyres are up to temp when it happens, no damage, minimal wear.
    Lap after lap, the rear tyres are heating up and don't seem to cool down properly in straights.

    The weird thing is that if you make a contact against an armco for example, the problem disappears.
    The braking is instantly back to normal. No more wandering in straight and the rear tyres start to cool down again.
    After that, I can drive as fast as before.

    In the following footage, you can see :
    - 1 lap without problem (0=>2:37)
    - some evidences of stability issues / overheating issues (2:38=>5:37)
    - Everything back to normal after the impact on armco. (impact around 5:40=> to end)

    I didn't try on another track by the way.

    The video is now online, please ignore my driving skill ^^ :




    EDIT:

    Some more testing and clues :

    Contact patches and vectors with max rear toe out :

    Full gaz / straight before bug

    Full gaz / straight lap 8

    Stop / lap 8

    Stop after impact / Lap 8
    Last edited by ironik; 17-08-2015 at 08:25.
    aka Ironik

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  2. #2
    GT3 Pilot Schnizz58's Avatar
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    I noticed that in the middle section where the car is unstable, the force vectors of the rear tires point more inwards than when the car is operating normally. It's as if the rear toe-in changed all by itself and then bashing the Armco straightened it out again. Anybody else notice that or is it just my imagination?
    Last edited by Schnizz58; 13-08-2015 at 21:05. Reason: typo
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  3. #3
    Kart Driver r3dm15t's Avatar
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    This is exactly what i experienced in the race, last night.. i also have some video evidence and profiled as well.
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  4. #4
    GT5 Pilot NemethR's Avatar
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    Quote Originally Posted by ironik View Post
    Hi,

    Some TGC guys and I have found something weird with the BMW 320 T @Silverstone GP.
    It's 100% reproducible.

    After some laps (7 or 8) the car starts to wandering right and left in straights.
    During the braking, the car is unstable. It's like the rear wheels are locking up and the car is waving. I have to countersteer while braking.
    It's not a proper tyres locking as I'm in fact applying less brakes than before the issue occured.
    The tyres are up to temp when it happens, no damage, minimal wear.
    Lap after lap, the rear tyres are heating up and don't seem to cool down properly in straights.

    The weird thing is that if you make a contact against an armco for example, the problem disappears.
    The braking is instantly back to normal. No more wandering in straight and the rear tyres start to cool down again.
    After that, I can drive as fast as before.

    In the following footage, you can see :
    - 1 lap without problem (0=>2:37)
    - some evidences of stability issues / overheating issues (2:38=>5:37)
    - Everything back to normal after the impact on armco. (impact around 5:40=> to end)

    I didn't try on another track by the way.

    The video is now online, please ignore my driving skill ^^ :

    I can second that, I had the exact same issue in the race (in the other race).

    After around 10 laps, the car was going left-right-left-right in the straight.
    It fixed itself when I was going into the pits for new tires.
    Roland | Németh
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  5. #5
    WMD Member ironik's Avatar
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    Quote Originally Posted by Schnizz58 View Post
    I noticed that in the middle section where the car is unstable, the force vectors of the rear tires point more inwards then when the car is operating normally. It's as if the rear toe-in changed all by itself and then bashing the Armco straightened it out again. Anybody else notice that or is it just my imagination?
    Maybe you're onto something here. In my vid we can see that the rear traction circle seems much more present in straights whereas not so much when there is no problem (traction circle fading).
    But honestly, I can't really "read" that. Same apply for the vector. (I suck at maths ^^)

    EDIT : After watching it again, yeah you're definitely right. Something is changing regarding contact patch.
    Still, I can't explain why it's making the car unstable on braking / straights. The vector makes me think there is more toe in => should be more stable. ^^ (regardless the bug)
    Last edited by ironik; 13-08-2015 at 20:48.
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  6. #6
    GT3 Pilot Schnizz58's Avatar
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    I could see too much toe-in causing sort of an oscillation as the two rear tires push against each other. The car wiggles one way slightly causing that tire to push back harder, causing a wiggle in the other direction and it does the same thing, lather, rinse repeat. I don't know if that's a plausible physical explanation or not.

    This is actually kind of similar in a way to the so-called "landmine" bug where the car suddenly flips up into the air for (usually) no apparent reason. In both cases something glitches in the game physics seemingly spontaneously.
    Last edited by Schnizz58; 13-08-2015 at 21:16.
    97.8% of mass public shootings in the US between 1950 and 2018 occurred in so-called "gun-free zones".
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  7. #7
    WMD Member ironik's Avatar
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    Ok, I tested with max toe in (0.9) : No problem of wandering or instability out of the box but the problem did occur sooner. (around lap 5 and noticeable around lap 4)
    I'm gonna test the other way around ^^
    Last edited by ironik; 14-08-2015 at 08:08.
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  8. #8
    GT3 Pilot Schnizz58's Avatar
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    Tire wear could be a factor also but I don't know how bonking the barrier could possibly reset it.

    In the telemetry HUD did the tire vectors point in the same direction as in your video?
    97.8% of mass public shootings in the US between 1950 and 2018 occurred in so-called "gun-free zones".
    ASUS GL702VI-MH72 | Thrustmaster TX Wheel | Thrustmaster VG Ferrari 599XX EVO Wheel Alcantara Edition
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  9. #9
    WMD Member ironik's Avatar
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    Tire wear is normal. around 10% IIRC.
    Well, with max toe out (0.9) the problem did occur at the same time than default toe.
    But you were spot on regarding contact patch and the vector :

    Full gaz / straight before bug

    Full gaz / straight lap 8

    Stop / lap 8

    Stop after impact / Lap 8
    aka Ironik

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  10. #10
    WMD Member ironik's Avatar
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    Quote Originally Posted by Schnizz58 View Post
    This is actually kind of similar in a way to the so-called "landmine" bug where the car suddenly flips up into the air for (usually) no apparent reason. In both cases something glitches in the game physics seemingly spontaneously.

    We had plenty of that yesterday (dip'n'flip) with group A. Maybe it's related yeah. The ford Capri didn't have the same problem though.
    Last edited by ironik; 13-08-2015 at 22:18.
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