I suggest doing this with a new system from the RoR creators called "BeamNG" using the Torque3D engine.
It will allow you soon to create your own races and events or which ever within a game. Its game engine in a game if that helps you...
Its still in early Alpha and races being added shortly.
RoR however never actually had an planned release. RoR also didn't have an AI system, this does already.
This does,
Game: $15 http://sites.fastspring.com/beamng/product/alpha
Recent Development: http://www.beamng.com/blogs/
Its worth it really.
We here are already developing monster trucks for the game.
The game is going to have an update pretty soon with:
-Core physics increased by 20%, those who lag will probably lag less unless you use integrated graphics.
-New road textures
-Compatibility for heavy machinery (semis) *cough monster trucks cough*
-Lua Coding, makes debugging and coding a lot easier
-Normal fixing, no more flickering textures on roads
-Racing system, create and edit races on any map by triggers, will work with AI soon
-You can edit the paint of the trucks within the game.