Just some supplementary information on this...

There are 46 events (40 trophy + 6 TT) and the progress rewards at 25-50-75-100% are 9-15-21-32GC. The last 4 cup races all need the final PR86 - tier 19 has 3, and tier 20 just 1 (which is five laps at Le Mans paying 13,100 Fame).

Alternatively, if you're just looking to get to 75% your car/one of your cars needs to reach PR83.2 for the cup race on tier 14: