Here are the part numbers and spring rate. The higher the rate the stiffer the spring. Also here is a link to amain to the shocks.
click here
LOSA5456 Team Losi 15mm Shock Springs 3.1" x 2.5 Rate (Red)
LOSA5457 Team Losi 15mm Shock Springs 3.1" x 2.8 Rate (Silver)
LOSA5458 Team Losi 15mm Shock Springs 3.1" x 3.1 Rate (Green)
LOSA5459 Team Losi 15mm Shock Springs 3.1" x 3.4 Rate (Black)
LOSA5460 Team Losi 15mm Shock Springs 3.1" x 3.7 Rate (White)
LOSA5462 Team Losi 15mm Shock Springs, 3.1" x 4.3 Rate (Purple)