Me too. They seem to have no effect at all, far as I can tell. And there's no indicators telling me if I'm increasing or decreasing while moving it to left or right. Sliders of mystery. Maybe it's a thing of faith -> If you strongly believe the car has more grip after sliding them around, it will have more grip.
I couldn't agree more on the placebo effect. Earlier on today, I played with the "gear ratio" slider (or whatever name it has), believing I would get shorter ratios. And indeed, I was shifting up earlier! But the acceleration and top speed hadn't changed... It was all psychological