Lost vibration when cornering and become very very understeering with elite controller。

Hello all
I am very troubling a question in FORZA7 , always Lost vibration when cornering and become very very understeering 。(Especially U-turn),I use elite controller。。。
For example:Driving Chevrolet C7.R at Suzuka circuit’s U-turn (#11?),and Lost vibration will happen very frequently.
I tried to reduce the vibration intensity.Although there are some improvements, it will happen occasionally
Does anyone know why, please help me to fix this.

thank you