A race class like a Z class would be pretty cool but would only fit extremely fast or above the mark of a 110 Race Class Rating vehicle. Such vehicle are not much In the game
The Z Class would go to 110 and so on. The only valuable vehicle that could enter this category are the supersonic one
Those being the BloodHound
The Thrust SSC as an exception since in theory, it shouldn’t be considered one with it’s Race Score
The Egoista (only if maxxed out and have the best spoiler)
The X100 (Tuned and lowest gear ratio)
The Dragster aswell as an exception
Same goes for the Jet Truck even with it’s mediocre Acceleration for it’s purpose
And for the last, Exo Speeder
As said earlier, many factors can make a vehicle that would typically be X but with a bit of digging should be in a higher tier class but, since they have downside compared to what would be a real Z class vehicle, they are low in the class