ME-student: Oops, just too busy and forgot to write some results here...
I installed the 2.1mm HB upper deck to my Pro3 and its steering action no more 'stalled'!!! The car can now steers through corners immediately!!
The car is now so rigid that it 'skids' somehow. So I can no longer use HPI grey spring all around. I use HPI pink spring #6849 at the rear.
