Genuine HPI quality option part for easy upgrading and hopping up! HPI Pro Linear Springs are ideal for tuning your touring car's suspension and handling characteristics. They will fit a wide variety of touring car shocks and are available in a huge range of stiffness so you can tune for any track condition or driving style.If all you have is the stock springs for your car, start with 2 sets of springs, with one set a bit softer than your stock springs and one set a bit harder. (One 'set' of springs is 2 pairs of springs, for 4 total springs) As you progress in driving skill, get another 2 sets of springs, again with one set a bit softer and one set a bit heavier. The more you drive, you'll develop experience in what changing springs does to the car, and you can try various combinations of springs. As a general starting point, most racers use the same springs front and rear, or slightly harder springs in the front. See below for kit reference.