choosing between diffrent kinds of fuel would be nice. for example gas, elecricity, petrol and diesel and everything has it's own pros and contras. for example diesel and petrol engines have more power but the tank weights more while gas tanks have less weight since they are literally filled with air :D
I have some ideas for the game. There should be an edit blueprint option if the part is lvl 0 because it's a pain to create a new part every time you need 5 more max weight.
Next maybe a bank that has also the possibility to store money and get interest back depanding on how long the money was there.
Another idea that I think would improve the game is diffrent kind of competions. Short distand races where acceleration is important, long distand races where max speed and fuel reach is important, car shows where appearance is important and so on.
My next idea is, instead of deleting unwanted cars and parts, puting them into an archive would be nicer. Then sometimes events happes like a person needing repair parts for an old timer or something like this.
Last I think that the user interface should be rearranged a bit. Market/production and research/design should be next to each other while statistics, info and settings should be at the bottom.