Harley-Davidson motorcycles are known for their unique design and character, and one characteristic that riders often notice is the slight shaking or vibration at idle speeds. This shaking is commonly referred to as "Harley-Davidson shake" or "Harley shake." There are several reasons why this occurs:
Engine Design: Harley-Davidson motorcycles typically use large, air-cooled V-twin engines with a 45-degree angle between the cylinders. This engine configuration creates an inherent imbalance in the engine's primary forces, resulting in some vibrations. Unlike inline or horizontally opposed engines that have inherent balance, V-twin engines have a unique firing order that contributes to the shaking.
Crankshaft Design: The V-twin engines used by Harley-Davidson have a single crankpin design. This means that both pistons share a common crankpin on the crankshaft, resulting in a firing order where the power strokes of the two cylinders are not evenly spaced. This uneven firing order causes additional vibrations.
Solid Engine Mounts: Harley-Davidson motorcycles traditionally used solid engine mounts, which transmit more of the engine's vibrations to the frame and, subsequently, the rider. This design choice was intentional to enhance the feel and character of the motorcycle.
Heavy Flywheel: Harley-Davidson engines have relatively heavy flywheels compared to some other motorcycles. The flywheel's mass helps smooth out power delivery and contributes to the distinctive feel of a Harley-Davidson motorcycle. However, it can also result in more noticeable vibrations at idle speeds.
It's worth noting that Harley-Davidson has made efforts to reduce vibrations in their newer models. In recent years, they have introduced rubber-mounted engines and improved frame designs to dampen vibrations and provide a smoother ride. However, the characteristic shake at idle speeds is still considered a part of the brand's identity and is appreciated by many riders as part of the Harley-Davidson experience.