So the easiest way to maybe explain this is that most cars in this game have a redline that is not where max power is and some cars need to be shifted well before the redline.
Now if you have a setting in the tuning and in the gearing settings just have at the top you can set your own shift time. It doesn’t change your performance but just gives you a visual reminder to shift.
Maybe this idea can go well with this suggestion:
I would love this. And think this deserves more attention and votes. Adjustable shift light would be nice for each car. Like the dodge viper for example it doesn’t like redlined most people wouldn’t know to shift early for best performance.