We up the carrying capacity of the RockyMounts 2in Expandable GuideRail from its stock two-bike set-up to a three-bike rack with the GuideRail Single Add-On. This kit provides everything we need to ensure that the third-wheel to the day's bike adventure has a spot in the car. We love that it allows bikes to be loaded asymmetrically to eliminate any unwanted handlebar interference, and prevents contact with frames or forks by securing them with contact to the tires only.