I have a g27.
First off, I think its a mistake to turn environmental effects all the way off, because this function is what lets you know when your car is bottoming out.
To make the kerb rumble effects as subtle as possible, turn down overall effects strength in profiler (I have mine set to 50 percent), in the game set environment effects to 10%, and strength and weight up higher, the higher strength and weight is, the more subtle the environment effects will be when they are set at 10%.
I agree with connor caple, you need some linearity in this game, I use 70% and I use 270 degrees for my wheel in the profiler, with saturation at 100 percent in the game.
I've tried all other setups suggested but to me this gives you the most control, it does not tend to spin out as much...200 percent and 50 linearity while it feels the best and is the easiest to turn, experience has taught me that its to unstable when accelerating out of tight turns....