Progressive coil springs, also known as progressive rate coil springs, are an integral part of the suspension system in vehicles such as the LC79. They are designed to provide a more comfortable and controlled ride experience by varying their spring rate along their length.
 
The term "progressive" refers to the fact that the springs have a non-linear spring rate, meaning that the amount of force required to compress the spring changes as it is compressed further. The coil springs are wound tighter or more closely spaced at one end and gradually loosen or have a wider pitch towards the other end.
 
When the vehicle encounters small bumps or road imperfections, the softer initial section of the spring provides a smooth ride, allowing the suspension to absorb these irregularities with ease. As the vehicle encounters larger bumps or loads, the stiffer section of the spring engages, providing more resistance and preventing excessive compression.
 
This progressive nature of the coil springs helps to improve overall suspension performance, reducing body roll, excessive bouncing, and bottoming out, while still maintaining a comfortable ride. It also contributes to better handling and control when driving off-road or under heavy loads.
 
Progressive coil springs can be used as part of a suspension upgrade or as a direct replacement for the stock springs on a vehicle like the LC79. They are often made from high-quality materials such as durable steel to withstand the demands of various driving conditions.