Brake multiplier - This defines the normal brakes. (pedal brakes)
0.50 = Very slow braking. The car has to be very heavy of something if you use this...
0.75 = I guess this a good one for trucks. (At least I use this)
0.85 = This could be the realistic average value.
1.00 = Sports car brakes.
2.00 = For fun...
Braking strength multiplier - This is an odd one... I think it's "increase in brakes per second", as it was in C1-textfiles.
0.0 = You might think that now the car can't slow down, but it does, so nothing special here.
1.0 = This is probably the default value... no significant difference compared to zero, though.
750.0 = Suddenly, this feels as if the front wheels are locked when you use the brake pedal (although visually they still do spin)... that's why the steering will become harder during braking. The car also stops too quickly to be realistic... :-)