The purpose of tall tires on the front of drag cars is : the larger diameter of the tire gives the car a starting advantage of not creating a foul start (red light). Which is leaving before the green light . There are 2 small lights on the top of the "Christmas Tree" . The first light is activated by the front tire breaking a light beam . this is a "pre-stage light". 6" forward of this light is another set of beams called a "staging beam". In order for the "Christmas Tree" to be activated this bulb must be lit by the front wheels . After this the "Tree' is activated and the countdown begins . There is usually ,but not always, an amount of distance the front tires can roll forward before the "stage" bulb goes out and you commit a foul start . A taller tire allows you to roll forward more distance before the red light comes on and you are disqualified . Example : your front tire is 26" tall and you change to a 27" tall tire at the track . this give you 1/2" more rollout at the starting line. Not a whole lot but enough to win races . Really fast cars don't use this tactic because they need the front to stay down for stability at the finish line . Hope this helps . To Tall Tom from Tilton