SPIDER, a race maptype script is not there by default.
But I've learned of a way!
Create a blank text file called Race.Script.txt
Place it in Documents\ManiaPlanet\Scripts\MapType\TrackMania\
And do what SPIDER said. Load up the map, select the hammer, "Set map type", select Race. Close it out and save the map. It should now be a race map instead of platform.
I've tested it and it works.