to get a good value for brake bias, with a qualifier the gating function works well. This allows you to return a calculation based on a condition, and if the condition is not true there will be a discontinuity. This means no data is presented when the condition is false, so will not effect any min/max/average calculations.
gate([Brake Press F]>5, ([Brake Press F]/[Brake Press F]+[Brake Press R]))
Note that in this case, in order to get a percentage you need to open the More option in the math channel and set the Quantity of the channel to Proportion and Unit Percentage.