Pedal Force Required for Braking at 1.8g and 1g

[cheeoli]

Hi everyone,

I’m 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 doesn’t make any sense because the pedal force should be vice versa... higher pedal force for higher braking g’s.

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 isn’t as effective as two calipers in the front. That’s why braking at 1.8g requires less force.

Am I doing anything wrong here? Also it’s 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!

[acedeuce802]

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).

[Claude Rouelle]

Not worth to introduce yourself, Cheeoli?

[Jonny Rochester]

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.

[dynatune]

Hi Everyone,

Although this thread is old I just wanted to make any FSAE Team aware of the fact that there is a Free Excel Tool available for FSAE Teams to Design and Verify
the base Design Parameters of a Hydraulic Brake System on http://www.dynatune-xl.com/dynatune-bdm.html

BR,
dynatune