The Viper has a unique switch that allows you to secure the mount outside of the towers on your roof rack giving you more space for additional bikes or other gear. The switch also makes it possible to reposition the bike mount even while it is locked and loaded. The Viper carries just about any bike with a quick release wheel skewer. However, there are a few exceptions where one of our other mounts should be used instead. These exceptions include, but are not limited to, bikes with triple clamp forks and forks with dropout spacing (the distance between the forks at the tips) other than 100mm.