Performance Online offers standard and heavy duty rate rear coil springs for your 1960-72 Chevy C10 and C20 truck. Standard duty coils are OE quality and performance, restore proper vehicle height and suspension geometry. Maintains good steering control and headlight aiming. Prevents bottoming and is designed to carry standard to light loads. Heavy duty coils are designed to give the additional load capacity needed for vehicles which frequently carry a heavier than standard to medium load. Most heavy duty springs offer about a 25% heavier spring rate.