I would like to know all the rules of the hotlap mode for lfs world, and also if I can modify the car setup? Thanks racers.

You can apply any kind of adjustments to the setup you'd like for your car when doing hotlaps. When doing hotlaps, as long as you don't hit any objects or go out of track boundaries (like on grass), the lap will still count as valid.
Happy hotlapping!

For more information, see these articles on the LFS Manual:
* https://en.lfsmanual.net/wiki/Game_Modes/Hot_Lapping - hotlapping mode in general, and uploading hotlaps to LFSW
* https://en.lfsmanual.net/wiki/LFS_World#Hotlaps - descriptions/rules for the various hotlap rankings and charts, LFSW Hotlap UI detailed