Assuming frameTime has the right value, the code seems correct. Have you tried to print the value of addSpeed when the game is running at 60fps against when it is running at 30fps? There should be a factor of two between the two values.
Assuming frameTime has the right value, the code seems correct. Have you tried to print the value of addSpeed when the game is running at 60fps against when it is running at 30fps? There should be a factor of two between the two values.