CalOffroad Heavy Duty Platinum Series Rear Coil Springs are designed and manufactured in Australia using high-grade Australian made steel suited specifically to the Ranger Raptor running Fox coilovers. The Fox Coilovers feature internal bypass technology and we have built our coils to work on this Fox platform. Dyno testing has been carried out to ensure the coil rate is tuned to match the shock valving, achieving the smoothest possible ride.