When I try to play STK with a wireless 360 contoller on my Windows 7, The left and right triggers are registered by the game as pressed without touching them, which is an issue in 2 cases,
When triggers are Accelerate / Brake : As soon as the race starts, it gives you the accelerate penalty, other than that it works fine.
When the triggers are Fire / Turbo : It uses a powerup as soon as you pick it up. It is also apparent in Time Trials, you use your Turbos at the start which lead to the penalty.