Harley Davidson Rubber Vs. Rigid Mount

The rigid mount was the traditional method of mounting an engine to a Harley-Davidson motorcycle. Several engines in the lineup are still mounted in this fashion. The Softail's engine is notably still rigid mounted to the frame of the bike. This has been a part of the Softail's heritage for generations and continues to be a feature of the bike with the new 103B engine introduced for 2012.

Rubber engine mounts first came into use at Harley-Davidson in 1980. Prior to that time, rigid mounting had been the norm. The FLT TourGlide was the first bike to feature the new mounting system, but it spread over time. The Dyna line up appeared in 1990 and featured rubber mounted engines. In 2004, even the Sportster would get rubber mounts so that the Touring, Dyna and Sportster models all had rubber mounted motors, leaving the rigid Softails in the minority.

The primary reason that rubber mounts were introduced was to help reduce the amount of vibrations felt by the rider. Harleys for many years were notorious for the amount of vibration and shaking that they transmitted to the rider, making for what some felt was an uncomfortable ride, while others felt it was part of the authentic Harley experience. Rubber mounts isolate the motor from the frame. On a traditional old-style Harley rigid mount, every movement of the motor is transmitted directly into the frame, which creates a constant vibrating feeling for the rider. In newer bikes, this is combatted through the user of the internal counter-balancer.

The lack of rubber mounts on the Softail models was compensated for with the development of the "B" designated Twin Cam engines, introduced with the 88B Twin Cam engine and carried through to the current 103B. The "B" in the designation stands for "balanced." These softail engines have a special balancing mechanism that spins in opposition to the vibrations of the engine in order to smooth out the ride even in the absence of rubber mounts.