Well yes the names can collide with any preexisting variable, method or ruby command, there are too many to actually list but here are some of the simpler SP variables you should avoid: frame, a, b, x, y, leftx, lefty, rightx, righty, joyLX, joyLY, joyRX, joyRY, ...
Easiest way to get around this is to use names specific to your model: car_motor, car_steering, boat_motor, track_distance, ...
Also all names are case sensitive, so car, cAr, caR are completely different variables.