The Softail chassis has long been a challenge as the shocks are hidden under the frame which makes common adjustments difficult. The RAP (Remote Adjustable Preload) system allows for easy tuning of the shocks to account for changing loads or the addition of a passenger and is conveniently located behind the left passenger peg. Simply turn the knob in either direction to set the spring preload. Before purchasing or attempting to install shocks that are different than the OEM length, confirm that your wheel travel can be altered without causing clearance issues such as, swingarm/axle to exhaust contact as well as chain/belt guard or tire contact.. Heavy Duty Applications are recommended for bikes operating at or near the manufacturer's maximum load rating over 50% of the time..