These are the CDFs - Cumulative Probability Distribution Functions for the lap times registered in last year's PNWC finals for the GT Mod category.
For example, Chad (the green curve) was able to complete 90% of his laps in 11.72s or less. That is, he completed 90% of his laps in a time no grater than 10% of his best lap (10,65s).
At the same time, Cristian (the dark blue curve) was almost as fast as Chad in terms of his fastest lap (10.73s vs. 10.65s) but could complete "only" 78% of his laps in 11.80s or less (which is 10% more than his fastest lap).
We have been playing with this type of analysis for our own times and it has been useful in understanding the impact of different set ups in car/driver performance. For example, we have done the curves for running with different tires, front suspension springs or T-bars. Obviously, the differences in performance are a result of the overall set up, but the curves may help understand in a more "scientific" way the impact of individual changes.
There is some statistical foundations to these curves, but I won't bother you with them. The analysis is done in Excel, from the data generated by Zround.