Introduced in 2013, QA1s 51 Series is an improved version of the popular 50 Series. The 51 Series features an in-house machined body with a larger inside diameter for increased oil volume for better cooling. Crafted with hard anodized internals and a zero gas pressure design, the 51 Series provides the most grip on slick tracks and the best feel of any shock. Popular choice for many racers from dirt and asphalt in nearly every type of class. Works best on dry-slick dirt and asphalt tracks where traction is limited and also as an axle wrap up shock. Gives superior feel and grip on smooth asphalt tracks.