Our Tuning Hub can determine spring rates in a few different ways: You can rely on our recommendation, which will calculate the most appropriate spring rate for your bike in order for you to be able to use all your travel appropriately, and it'll calculate the sag for you from there. You can specify a preferred sag percentage (if you know exactly how much you want) Or, if you've already got a coil spring rate that you like on that bike, you can tell us what that is, and we can work with that. On top of that, Sprindex springs allow you to adjust the spring rate by around 10-12% (eg from 450-500lbs/in) to maximize the chances of you getting exactly what you need. However, mountain biking is a very personal thing when it comes to preferences, so if you find the spring we've recommended for you is too firm or too stiff, let us know - we can get you a sizeable discount on a replacement spring. We don't offer exchanges though, sorry.