Hello there !
I would like to know if there is a way to compute rank for a racing game in real time ? I know it’s possible to compute rank through triggers, but is there a way to know who’s first at any time like most racing game ?
Thanks in advance 
it is remarkably hard to do this. Basically you need markers every meter.
You can also use, likely in combination with this, a dead reckoning system on each vehicle based on the velocity.
By the way, it’s particularly difficult to handle checkpoints well in tight corners, and similar situations. Things like bridges can also cause trouble.
Finally - you are probably aware of this - you can use checkpoints, plus, a simple straightline distance from the most recent checkpoint. As long as the track is fairly straight between checks, and the track is not unusually wide relative to the vehicles, this can also work well.