This is an optional XRAY Progressive Long Rear Shock Spring Set, and is intended for use with the XRAY XB808 and XB9 1/8 buggies. These springs provide improved steering at the beginning of the corner, but will help to resist rolling in the middle of the corner as the spring becomes stiffer and are recommended for medium to high traction surfaces. These progressive rate springs are soft at the beginning of the compression, similar to 0.5 rate springs, but become harder as the spring is compressed through the middle of the stroke and finish off the compression at 0.6 rate.
XRAY springs are individually measured, and inspected to provide you with matched springs with identical damping characteristics. During the selection process each spring is compressed in several fine increments and the values are recorded. Each spring is then matched with another spring of identical characteristics providing you with the best springs possible.