Wait till my next release ;) and use Newton for this task.
The next release will have the fully vehicle capabilities of newton integrated. There you could split your racing level into different materials with every single one having there own properties and the wheels of the vehicle will react on them.
Without I would suggest a bitmap where you define your regions and the create a lookup table from this data. Then you only have to compare the current car pos (maybe wheel by wheel) with the table und you get the correct underground.
The next release will have the fully vehicle capabilities of newton integrated. There you could split your racing level into different materials with every single one having there own properties and the wheels of the vehicle will react on them.
Without I would suggest a bitmap where you define your regions and the create a lookup table from this data. Then you only have to compare the current car pos (maybe wheel by wheel) with the table und you get the correct underground.