Two-player racing on one phone: rotate first
In portrait, half the titles hide the second player's buttons. Rotate to landscape before you pick a game.
Half of all two-player titles hide the second player's buttons in portrait. Before choosing a game, rotate the phone to landscape and then open it. If the second control set only appears after rotating, that is a sign the title was designed for a split screen.
Split the screen clearly: player one on the left, player two on the right, each holding their own side of the phone. Do not leave the phone flat in the middle of the table, because nobody can reach the far buttons without covering the opponent's half.
For a fair match, look for a symmetrical track or one that swaps sides each round. If one player always gets the inside line, the game feels lopsided by the third round, and that is usually where it stops.
Also check whether the game rotates the display automatically. Titles that force portrait leave the split screen too narrow, and both players lose sight of the next corner.
Agree first on who holds the top edge of the phone. In a landscape split, one player faces up and one faces down, and that affects who reads the next corner faster.