Instead of make a ramp one big mesh, have you tried to make it of small pieces ?

I´m working in a race track, and is absolutelly difficult to model a track in wed, with smooth turns and so on. I made some nice turns in Med, skinned them and to my surprise my car falls when passing on them. I figured that If I downsize the turn like it have 2 x 2 Meters ( 10% of total real size ) then the car can collide with it. I read somewhere else that the grid size does matter... Anyway... I also didnt solved completely this problem.