Make an option in the 'Cars' screen in which you can select a default throttle profile for a car.
If this car is chosen in the 'Controller' tab and a user in the 'Event' tab, this profile must be selected for that user as the profile to race with.
This way a 'too fast' car can be restricted, without the need to manually select the right profile each time.
For the exact details concerning this functionality, additional thinking must be done.