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Thread: Pedal Force Required for Braking at 1.8g and 1g

  1. #1

    Pedal Force Required for Braking at 1.8g and 1g

    Hi everyone,

    Iím designing the brake system for our new car for 2019, but I have a few questions.
    We are running dual outboard in the front and single inboard in rear without a full aero package.

    According to my calculations the pedal force required for us to brake at 1.8g is 121lbf while braking at 1g is 144lbf.

    Intuitively this doesnít make any sense because the pedal force should be vice versa... higher pedal force for higher braking gís.

    However, mathematically I can see why it is this way because braking at 1g would require more braking force in the rear... and since we run single inboard, one caliper in the rear isnít as effective as two calipers in the front. Thatís why braking at 1.8g requires less force.

    Am I doing anything wrong here? Also itís impossible to be able to have a 50/50 brake bias at both 1.8g and 1g. What case should I focus on?

    Thanks a lot!

  2. #2
    Your calculations are wrong, you would have a higher pedal force at higher acceleration.

    Why do you want a 50/50 brake bias?

    Make an X-Y plot of "ideal" front/rear pressures at different accelerations (accounting for different caliper/master/etc front/rear), then overlay actual front/rear pressures taking your prop valve into account. Adjust parameters until these lines are close (or slightly front biased).
    Adam
    Any views or opinions expressed by me may in no way reflect those of Kettering University, it's students and administrators, or our sponsors.

  3. #3

    And you are?

    Not worth to introduce yourself, Cheeoli?
    Claude Rouelle
    OptimumG president
    Vehicle Dynamics & Race Car Engineering
    Training / Consulting / Simulation Software
    FS & FSAE design judge USA / Canada / UK / Germany / Spain / Italy / China / Brazil / Australia
    [url]www.optimumg.com[/u

  4. #4
    Cheeoli, your calculations may not necessarily be incorrect, but your inputs could be unreasonable.

    I have made my own brake force sheet in Excel and am able to replicate this condition with lower pedal force at higher deceleration (perhaps with silly input numbers).

    The main number that caused this is COG, center of gravity height. Under braking deceleration you generate a moment which gives higher tyre load on the front and lighter on the rear. This is part of my Excel calculations. If you accidentally input a COG too high, your calculations will show lower brake pedal force at higher decelerations. If this was replicated in life, it would be a front flip! Choose a lower COG.
    Last edited by Jonny Rochester; 10-14-2018 at 01:12 AM.
    University of Tasmania (UTAS)

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