My setup for the LWFF (with BB kit)
Game controler:

Most important I guess, as I read on this site:
Spring Gain:  0% (always off. GPL doesn't use Spring Gain. Having it on can cause spikes)
Text version:

*Note: I now use an Overall Strenght of 100%, it's worth trying if you have spikes.

Enable Force Feedback     yes
Enable Autocalibration      yes
Overall Effects Strength   100%
Spring Effect Strength      0%
Damper Effect Strength    0%
Enable Centering Spring    no
Centering Spring Strength  n/a


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If you use Profiler (I don't):
Text version, and other settings:

*Again Note: I now use an Overall Strenght of 100%, it's worth trying if you have spikes.

   
Global Overall Effects Strength  100%
    Global Enable Centering Spring  no
    Global Centering Spring Strength n/a

    Wheel Sensitivity   med
    Wheel Deadzone    low
    Accel Sensitivity   low-med
    Accel Deadzone    low
    Brake Sensitivity   low
    Brake Deadzone    low

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Core.ini:

      [ Joy ]
      allow_force_feedback = 1
      force_feedback_damping = 5
      force_feedback_latency = 0
      max_steering_torque = 200

I think that by having latency at 0, it does not guess what the forces will be, and I think it helps to not having spikes.  If you want some latency, it needs to be a very low number, for sure not more then 0.02 IMO.

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WinVroc:
Linearity: