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Help needed interpreting telemetry graph elements (pcarsprofiler)

Discussion in 'Automobilista - General Discussion' started by Sunscreen, Oct 12, 2021.

  1. Sunscreen

    Sunscreen Active Member

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    Hello all, I thought I would throw this out there to the community as I know what a depth of talent and expertise exists out there. Its a fairly straightforward question really. In the attached picture Ive highlighted some areas with a blue pen. One is tyre grip levels on the long left hander at Hockenheim and the other the hairpin at the end of that straight. I see the grip levels fluctuating on the telemetry but what is this actually telling me, what interpretation should I be deriving from it? The second element is what is the relationship Im seeing between brake application and grip levels in the highlighted area where the red vertical line sits? This is the heavy braking zone at the end of that straight. At peak braking application it looks almost to me like there is an increase in grip (the dip in the grip trace)? Its this kind of interpretation that Im falling down on at the moment and which would increase my enjoyment of tweaking things like brake pressure, balance and suspension in the setup process.
    If anyone has any other telemetry interpretation advice Id appreciate it.
    Thanks in advance :)
    hock braking.png
     
  2. Shriukan

    Shriukan Touristenfahrten Community Reiza Backer

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    While the fronts grip, the rears have lower grip as the rear of the car pivots forwards.

    If you lock up your fronts, the front wheels aren't stopping the car and thus they are not shifting the weight forwards (or at least much less), thus the rear wheels and their brakes come much more into play. In other words, a front lockup increases rear grip as the rears have more load.
     
  3. Sunscreen

    Sunscreen Active Member

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    Ahh ok good description, that makes sense to me. What do the dips in the grip trace suggest at the point where the red vertical line sits? Its that kind of detail Im hoping to unpick. That dip is on all the tyres and its occuring at maximum braking input, and looking at the rest of the lap when the grip line is lower that equals more grip?
     
  4. Sunscreen

    Sunscreen Active Member

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    Also Im really curious about why the grip is fluctuating so wildly on the rear of the car in a section of track that is really just a gentle curve (the blue rectangle). It makes me think its indicating maybe a rebound issue or something?

    Another possibility is that Im fundamentally missing the presentation meaning of the graph. So is it indicating the current application of the available grip (in the sense of the potential available grip is 100% and at a given moment the graph indicates what % of the potential is in use)? Or is it something else? Understanding this is fundamental to understanding those dips at the point of maximum braking I think.
     
    Last edited: Oct 12, 2021
  5. Shriukan

    Shriukan Touristenfahrten Community Reiza Backer

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    So there are a few things to take into account. As you drop the brakes you are still braking enough to keep the fronts locked. However you have also dropped enough rear braking force and as such the whole mass of the car is being placed on the fronts which, while braking, were being assisted by the rears and now they have no help. Thus the total loss of grip on already and still sliding fronts.

    As for the spikes in the long turn, minor road bumps, minor input changes and gear changes are all causing a reaction on the car and that includes the tire grip. But this doesn't mean your total grip available is being overcome. It just means a bump or left movement of the wheel or a gear shift (as power is put down again) puts more weight on the right side (which puts force onto the tires) and thus increases grip to then lose it as the suspension and tires relax. The suspension then compresses and relaxes a few more times, each time more lightly as the damper does its thing. I'd say as long as the grip and drive feels stable, you don't need to worry too much about perfecting the damping in that section.

    The graph is showing total grip but to better dissect and understand, the graph should've been split between longitudinal and lateral grip.
     
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  6. Sunscreen

    Sunscreen Active Member

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    Nice explanation, thank you :) There is actually an option in the software to split the grip display graphs as you suggest and now the utilisation of that makes sense. Appreciate it!
     
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  7. Sunscreen

    Sunscreen Active Member

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    Ok Ive figured out what specifically the grip graph indications are telling me so I thought I'd share my thoughts for the benefit of anyone else beginning their understanding of telemetry.
    It appears that the best way to think of the data presentation is as a Total Adhesion Display. A very poor choice of words I admit but it functions in my understanding as follows:
    While driving along a straight there is little actual adhesion taking place in the sense of required lateral or longitudinal grip. The tyres are rolling across the surface without much friction, or adhesion for want of a better word. Thats why in the attached display the graphs show 0% at the point where I put the question mark. The slight long left hander leading to the hairpin has a demand of adhesion due lateral and slight longitudinal accelerations so it registers that demand with the messy spikes. When I braked for the hairpin all four wheels locked up (I'd deliberately set the braking force too high) and there is an initial demand on adhesion which is rapidly exceeded and the wheels start sliding so total adhesion is lost, so initial rise in adhesion until its lost then back to zero is reflected in the traces for all four wheels. Earlier in the lap I lost front end grip under braking and this is clearly shown too. This is why I believe the graph shows zero % grip along the straight but also in the heavy braking zone.
    Hopefully this makes sense :confused: It does to me now :p
    InkedHockenheim Test Three_LI.jpg
     

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