When it comes to coilovers, preload is one of the most important aspects that affect stiffness. By definition, preload is the initial tension placed on a spring before any load is applied. In other words, it's the amount of force required to compress a spring from its free state to its installed state. The higher the preload, the stiffer the spring will be.
Now that we know what preload is and how it affects stiffness, let's take a look at how it works in relation to coilovers. Essentially, when you adjust the preload on your coilovers, you're changing the amount of force required to compress the springs. The more preload you have, the stiffer your suspension will be. Conversely, less preload will result in a softer ride.
It's important to note that adjusting preload will not only affect stiffness, but also ride height. More preload means higher ride height, while less preload will result in a lower stance. So if you're looking to lower your car without sacrificing performance, dialing in the right amount of preload is crucial.
In short, yes - adjusting coilover preload can definitely affect stiffness. But as with anything related to suspension tuning, it's all about finding the perfect balance for your specific setup and driving style.