I just tested Normal and Hard difficulty level, and I manage to make clean laps without releasing Throttle (Monza), need to use brake/ lift of throttle only when "racing" other cars. But their racing line and behavior are far from perfect at the moment and they actually a pain to race with.
On the test track I need to brake on "U" shaped corners, there is a strange feeling that car loose its grip depending on how long I hold turn key (without throttle at the time)
Also you need to work on a collisions between cars as well I think, as now it's breaking the experience. Too much slow down per "bump". Also on some "hit" angles cars should carry on speed without slow down (when you bump side to side for example).
things I will change
- At the moment you have 3 difficulty levels, maybe to make it more "cool" let player to choose different spec cars (more power/less grip etc that will represent Easy, Normal, and Hard levels... basically same thing just represented in more fun way I think.
- What about changing camera position slightly so you can see more stuff ahead of car instead of having a car in the center.
- Think about adding tyre marks to your tracks, to let player know about braking points, racing line etc.
- Car slowing too much when on the grass/off track, it is frustrating, To penalize player I would slow down slightly but add something like a damage to a tyres to reduce grip level. you go off many times so you damage tyres more and will lose anyway.
I don't know how complex you wanna make it so you may find this stuff irrelevant for your project.