In sims, we tend to judge this by sight (wheels stop turning) or sound (screech of locked wheels). This can be difficult, especially with closed wheel cars when visual signals are not available and the aural is difficult to judge.
When we calibrate within GPL, we move the brake pedal to its maximum extent and get a reading of 1000 which is way beyond the locking point - which anyway varies according to car.
It seems that the greatest braking effort is affected when the electric resistance in the ‘braking’ circuit is at a minimum. So adding (electrical) resistance in that circuit will reduce the braking effort and get below the locking position.
On my wheel/pedal assembly, a Logitech DFP, I have put a 10KOhm variable resistor in the braking circuit, This new pot is used for adjustment after calibration in GPL. I also modified the angular movement/feel of the pedal by use of a rubber wedge cut from a fairly rigid rubber ball which is attached to the underside of the brake pedal arm with Velcro. This means that the pedal assembly may be returned to its original state. I did however, cut away a little from the front of the pedal box so that it is easier to place and replace the wedge.
The full procedure works like this. The pedal is calibrated in GPL, depress fully, wedge compressed, to 1000. Close the calibration window and take the car to the track, take it up to full speed and brake hard. Brakes will lock. By adjusting the variable resistor, bring the braking effect back to the pre-lock area and you have a pedal that moves quickly in an angular movement until it reaches the wedge, where braking starts and then increases to the verge of locking with added pressure.. You will probably need a couple of laps to warm up the tyres before you get the proper effect.
In my original experiment, I sited the added variable resistor on the pedal base, but later moved it into a little box which is attached to the side of my wheel mount by Velcro and I made the connection from pedal base to adjuster box by cable and two 1.5mm microphone/earphone sockets and plugs, one in the pedal base and one on the box. This allows the pedal box to be returned to its original electrical state. .
I checked in which line the variable resistor should be placed by preparing all the extra bits. With the pedals dissembled, but connected to the GPL calibration window and brake pedal ‘depressed‘, I put the new potentiometer in circuit and increased the resistance. When this shows the calibration figure dropping, you’ve got the correct one. On the DFP the correct tag is the bottom one on braking potentiometer that has the red wire connected to it.
You could do it with one set of socket and plug on the pedal box and direct cable attachment on the little box, but I had two sets and used them for convenience.
You need to be able to use a soldering iron, I got the connectors from a model shop (model railway items) and the small box,10Kohm potentiometer, calibrated knob and earphone sockets and plugs from Maplin. The whole lot cost me a few pounds. I found difficulty in working out which tags connected to which part of the earphone sockets at first but worked it out in time !
A few points.
1) Be careful re-assembling the pedal box, NEVER force it together, the original pots are carefully located by cut outs and must fit smoothly.
2) Ensure that the thick part of the wedge is at, or near, the outer end of the brake pedal arm and not near its pivot to reduce strain on the joint and arm.
It sounds rather complicated, but really it is simple enough if you can solder and it has added greatly to my enjoyment. I hope it may do so to a few others.
I do not know if this will work with all wheels/pedals but do not see why not.
HOWEVER YOU DO THIS AT YOUR OWN RISK, I WILL NOT BE RESPONSIBLE FOR ANYTHING THAT GOES WRONG OR BREAKS !!!