Thanks to Lotus III's RECS custom track creation tool, there can be millions different tracks. So, Racer Community work about that and created a list : These are most known Custom Track Codes which are created Racer Community :

Code Effect

evilracin-[00-99] - Highway race challenge-[00-99] - Enable wind effect and turn physics. character-[00-99] - All scenarios +80% (except length and obstacles). wrongways-[00-99] - Alternate Jupiter race. sharpness-[00-99] - Alternate Mountain race. callmebob-[00-99] - Alternate Windy race. get enemy-[00-99] - Difficult enemies. sceneries-[00-99] - Mountain race with turbo. steepness-[00-99] - Mountain race with first column +80%. amcodpsnr-[00-99] - Windy race on turbo. jkvuawhrm-[00-99] - Foggy forest race. highspeed-[00-99] - Forest race at high speed . kkkkkkkkk-[00-99] - Forest race with only curves, six laps and mountains. mrgihwpvq-[00-99] - Swamp race with a lot of hills. mrgixwpvq-[00-99] - Swamp race with no hills. uhqjcyawl-[00-99] - City race when dark. ftfyxsmuq-[00-99] - Desert race. qoxzxjqml-[00-99] - Moonlight race. nlgiodzbn-[00-99] - Mountain race. odbssziux-[00-99] - Arctic race. letsmosey-[00-99] - Rainy race. eznuyfjpb-[00-99] - Highway race with farmers on the road. racingfun-[00-99] - Oily road race. xxxxxxxxx[00-99] - Oily road race with no curves. pvtumjbqt-[00-99] - Orange planet race. pvmqrwhak-[00-99] - Orange planet race with turbo. obstacles-[00-99] - Snow race. Space (9x)-XX - Golden middle way.