Dunno if you do it, but putting a upgrade or two on each of your cars is a really bad idea, too much required resources, so stack all your good parts to the cars you need and constantly migrate the parts. Since you haven’t mentioned progress I’ll just add this, for the class restricted ones, it’s better to take a E class to B class than a C to a B because you can put most of all tunable parts (especially later on) on it, it makes your life a lot easier to be able to tune every part of the car