Mario Kart 8 Total Coins Collecting Logic
Solution 1:
The number of coins added to your total is the number of coins that each local player has at the end of each race. This means that you can get a maximum of 10 coins per race with one player, but 40 coins per race with four players.
Although you can collect enough coins to unlock multiple parts in a single grand prix or VS match, you can only unlock one part at a time. You must then return the the menu after viewing the newly unlocked part to receive any further parts that you have enough total coins to unlock.
Solution 2:
It's the coins collected at the end of the race. It can be possible that you have multiple unlocks in a row after a grand prix, for example if you start with 95 coins.
- After grand prix 1, you can have 135 coins, and unlocked something
- After grand prix 2, you can have 175 coins, and unlocked something
- After grand prix 3, you can have 205 coins, and unlocked something
After GP4 it stops, but in one grand prix you have again a coin amount just under 50, so you'll unlock again in a row. If you quit or restart the grand prix after a few races, you still obtained some coins. Therefor it isn't necessary to get 40 coins every grand prix.