The scoring is explained in this thread: http://forums.ubi.com/showthread.php...ring-Explained
Let's compare Turbine Terror and Inferno IV.
Platinum time for
Turbine Terror: 0:46.3
Inferno IV: 2:00
Ultimate time for
Turbine Terror: 0:35
Inferno IV: 0:35
The platinum time for every track gives you exactly 322500 points and the ultimate time gives you 360000 points.
The difference between platinum and ultimate times in Turbine Terror is 11.3 seconds.
In Inferno IV it is 85 seconds.
85/11.3 ≈ 7.5
In other words, for improving your time by 1 second in Turbine Terror, you'll need to improve your time 7.5 times that in Inferno IV to get the same increase in score.