The clunking sound often associated with Harley-Davidson motorcycles when shifting gears is primarily a result of their design and transmission system. There are a few reasons why this clunking sound occurs:
Transmission Design: Harley-Davidson motorcycles typically use a manual transmission with a traditional "constant mesh" design. In this design, the gears are always engaged but are not locked together. When shifting, the rider disengages one gear and engages the next. The clunking sound is caused by the engagement of the new gear.
Heavy Flywheels: Harley-Davidson motorcycles often feature heavy flywheels as part of their design, which contributes to their signature low-end torque and distinctive riding experience. The mass of the flywheel, combined with the design of the transmission, can result in a more pronounced clunking sound when shifting.
Mechanical Tolerances: Every motorcycle has a certain level of mechanical tolerances, including gaps and clearances between the various transmission components. These tolerances can cause some noise and clunking during gear engagement, especially if the parts have worn over time.
It's important to note that while the clunking sound may be considered a characteristic of Harley-Davidson motorcycles, not all riders find it bothersome or undesirable. In fact, for some riders, the clunking sound adds to the overall charm and character of the Harley-Davidson riding experience. Manufacturers continually work to refine their transmission systems and reduce noise, but certain design elements and the desire to maintain the traditional Harley-Davidson feel may result in some degree of clunking during gear shifts.