On race driver grid is your teammates money taken from your winnings

No, They get their percentage of what they actually won in the race.

Say you got first, and they got second overall. 2nd is worth 2,000,000. They get a percentage of the 2 mil, and you get everything else.
Thus you get all, their sponsor money, team win, etc.


So, there is no reason not to get a good team mate, I played most of the game with a poor one, but there is no real reason for it, as you have nothing to lose.