The one armed gear shifting in this game really felt so fun in this game and I don't know how you implemented a full engine system with proper rev calculations but well done honestly! One thing is I went too fast into a wall and ended up somehow inverting all the gears and the controls (i.e. All forward gears made me go backwards and turning right made me go left).
Viewing post in Half Grip jam comments
Yes, the rev calculation system was a pain, initially it was fully physics based (simulating the clutch as a angular velocity torque spring between the wheels and the engine, with proper engine power curves) but that proved to be too hard to tune for good gameplay, so the whole code was scrapped and the final one is halfway between that and something more fun and easy to adjust. But some more bugfixing is required :)