These terms apply to automotive suspension coil springs.
Active Coils: Coils which are free to deflect under load. Also referred to as working coils.
Approx. Lowering: The approximate amount of chassis ride height reduction. This will vary depending on optional equipment: gas shocks, age of stock springs and upper strut bearings.
Bottoming Out: The suspension reaches its maximum compressed height, not when tires rub fenders or contact the chassis.
Dead or Inactive Coils: Coils, which are in contact with adjacent coils at loaded height. Inactive coils do nothing but give the spring enough free length to stay tight in the spring perches at full rebound.
Deflection: The travel of the spring as it is compressed.
Foamy Bumpstop: Also referred to as a supplemental spring, a progressive-rate urethane jounce bumper will make the suspension progressive. Gives a smooth transition to full compression.
Free Length: The overall length of a spring in unloaded position. May also be referred to as UN-INSTALLED LENGTH.
Full Jounce, Full Compression: The suspension is completely loaded. The springs and bumpstops are totally compressed.
Full Rebound, Full Droop: The suspension is completely unloaded. Example: When the vehicle is on a lift and the tires and wheels are hanging in the air.
Linear Spring: One rate throughout the springs working range.
Loaded Height: Or INSTALLED HEIGHT, is the length of the spring compressed under the load of the vehicle weight, when the vehicle is at rest on level ground. Also may be referred to as STATIC HEIGHT.