If your bike has air suspension you really must have one of these to check your pressure every 4-6 months. A small drop in pressure of 5-10 psi can make a huge difference in how your bike will perform. All rockshox forks have an air chart on the left leg that corresponds to a riders weight and fox have finally started labeling theirs as well. For the rear shock you will need to know how to set sag, your local bike shop can do this for you. Once you know the pressure you are good to air it back to that point unless your rider weight changes.