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Braking distance - locked wheels vs. threshold braking

Discussion in 'Assetto Corsa' started by mmkay, Dec 8, 2013.

  1. Yesterday someone on another forum posted these 2 videos.
    It is Zonda R on both occasions, starting braking from the same speed exactly at the start/finish line.

    This video shows braking with locked wheels - no ABS

    This video shows threshold braking - no ABS

    Apparently the guy managed to stop the car faster with locked brakes.
    He wrote, that it shouldn't be like that.

    What do you think about it ?
  2. ABS won't always reduce the braking distance compared to locking the wheels up. It depends on so many factors that it's impossible to tell which stops the car quicker. I wouldn
    't say its a bug.
  3. There was no ABS used in these videos.

    I would say that this is definitely incorrect - sliding tires have nowhere near as much grip as rolling ones, it cannot stop as fast.
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  4. Ah, I misread stuff then. It is indeed kinda wrong then. Sorry,. my mistake.
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  5. Yesterday the sam guy, that posted about problems about braking distances with locked wheels made another thread about grip drop off at high slip angles.
    I will copy it here. Tell me what do you think about it ?

    Here is this thread:


    Is he talking rubbish or is AC not as realistic as we all thought ?
  6. I think cornering and being fast is a bit more complex than just a mathematical/physical solution. The angle of the turn is a big factor in that. Slipping 4 wheels into a low-angle turn won't make you faster at all, but doing that with a 90-ish degree turn would gain you tons of time, over trying to grip it all the way being smooth. Same with hairpins, but with even more slip angle. Of course you can be smooth while driving agressively. Using tires to their max potential doesn't equal using the optimal slip angle.
  7. The lateral force will drop due to acceleration and braking.

    (From the site he already linked in the quote http://insideracingtechnology.com/tirebkexerpt2.htm )

    If you don't change speed it won't fall off drastically. If you get higher slip ratio the peak will be "less peaky" (see the small text and images under "Combined Forces" in the above link) but overall forces will be less.
  8. Andrew Ford

    Andrew Ford
    Premium Member

    he is talking A LOT OF SENSE sadly.
  9. These tests really need to plot slip ratio of the tyres at the same time.

    They say they are threshold braking but because the peak slip ratio is so small, if they are just 5-10% before peak slip ratio then the overall force available might be the same for a hot locked slick tyre.

    You really can't judge based on a video like this, you need the tyre information.

    Even on the AC forum thread it's not clear.

    Not saying we shouldn't be checking this, or that there is actually anything right or wrong, but ultimately our test gear is sadly nowhere near good enough in this beta version to log and analyse what is going on.

    What you need is a plot of slip ratio and tyre force over many stops and then you can check the shape of the slip ratio vs force curve.

    I have a feeling that there are points in the curve where the force is much higher but it's such a narrow window that it's very hard to find and maintain.

    Consider that the tyre is heating up as you slow down, so gaining grip, and then perhaps over-heating and losing grip, so to hit that moving range of maybe 5-10% of the slip ratio curve where there IS more grip vs locked tyres, is gonna be damn hard!

    Technically it's either right or wrong, and easy to check. I'm sure Aris and guys know this by now so hopefully if there is an issue here it'll be resolved for a future update :)

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