If you select "Full" for "FFB Effects" on control options, you will get all sorts of canned (fake) effects on your wheel, including BRAKE feedback. If you don't like some of those or want to change their "volumes", you can change them on the Controller.ini file. These lines refer to those effects:
FFB steer force grip factor="0.40000" // Range 0.0 to 1.0, recommended: 0.2 to 0.6 (previously hardcoded to 0.4). How much of a factor the front wheel grip is on the steering weight.
FFB steer front grip fract="0.00000" // Range 0.0 to 1.0 (previous hardcoded value was 0.0), additional effect of front grip loss on steering force
FFB steer update threshold="0.00000" // Amount of change required to update steer force/vibe (0.0 - 1.0). Lower values = steering force updated more frequently = lower frame rate.
FFB steer friction coefficient="0.17500" // Coefficient to use for steering friction. Range: -1.0 to 1.0
FFB steer friction saturation="1.00000" // Saturation value to use for steering friction. Range: 0 - 1.0
FFB steer damper coefficient="0.17500" // Coefficient to use for steering damper. Range: -1.0 to 1.0
FFB steer damper saturation="1.00000" // Saturation value to use for steering damper. Range: 0 - 1.0
FFB throttle vibe freq mult="0.17000" // Scales actual engine frequency to force FFB vibration frequency. Suggested range: 0.10 to 0.50
FFB throttle vibe zero magnitude="0.09000" // Magnitude of engine vibration at 0rpm (reference point).
FFB throttle vibe slope="0.00000" // Slope of line defining magnitude as a function of frequency (used with FFB throttle vibe zero magnitude).
FFB throttle vibe wave type="0" // Type of wave to use for vibe: 0=Sine, 1=Square, 2=Triangle, 3=Sawtooth up, 4=Sawtooth down.
FFB throttle vibe update thresh="0.08000" // Amount of change required to update throttle vibe (0.0 - 1.0)
FFB brake vibe freq mult="0.90000" // Scales actual brake rotational frequency to force feedback vibration frequency.
FFB brake vibe zero magnitude="0.10000" // Magnitude of brake vibration at 0mph (reference point).
FFB brake vibe slope="0.00000" // Slope of line defining magnitude as a function of frequency (used with FFB brake vibe zero magnitude).
FFB brake vibe wave type="0" // Type of wave to use for vibe: 0=Sine, 1=Square, 2=Triangle, 3=Sawtooth up, 4=Sawtooth down.
FFB brake vibe update thresh="0.05000" // Amount of change required to update brake vibe (0.0 to 1.0)
FFB rumble strip magnitude="0.25000" // How strong the rumble strip rumble is. Range 0.0 to 1.0, 0.0 disables effect.
FFB rumble strip freq mult="0.60000" // Rumble stip frequency multiplier 1.0 = one rumble per wheel rev.
FFB rumble strip wave type="0" // Type of wave to use for vibe: 0=Sine, 1=Square, 2=Triangle, 3=Sawtooth up, 4=Sawtooth down.
FFB rumble strip pull factor="-0.50000" // How strongly wheel pulls right/left when running over a rumble strip. Suggested range: -1.5 to 1.5.
FFB rumble strip update thresh="0.07500" // Amount of change required to update rumble strip effect (0.0 - 1.0)
FFB jolt magnitude="1.00000" // How strong jolts from other cars (or walls) are. Suggested Range: -2.0 to 2.0.
Change them as you wish but always keep a copy of the original file, just in case.