Traxxion Dynamics recommends Hyperco Shock Springs exclusively. Hyperco springs are used at the highest levels of motorsport to include Indy Car and NASCAR. Their springs are manufactured to far stricter tolerances than any other aftermarket spring. Available in their distinctive royal blue color only, people will know you have picked only the best product for your machine. Hyperco Springs are the original equipment springs on all Penske Racing Shocks, and that should speak for itself!