I think the gyroscopic forces developed by a spinning mass are applied at 90 degrees to the "axle" of the spinning mass. Hence, a spinning wheel remains vertical. If you hold a bicycle wheel by the axle and spin it, it resists an attempt to rotate the axle either in a horizontal or vertical rotation. But if you are holding it vertical (axle horizontal) straight out in front of you and raise your arms, there is no effect on the wheel. Likewise with a "V" twin - the mass of the flywheel is spinning in the same plane as the wheels (axle side to side) and thus provides stability in a vertical plane (helping to keep the bike from falling over). However, a flat six, with the "axle" of the rotating mass (flywheel, crankshaft, alternator and trans gears) in a longitudinal direction (front to back) does not provide any gyroscopic stability along its axis so there is no vertical stability provided as the bike leans from side to side. If all the rotating parts of the flat six are spinning in the same direction (which Honda does not do), you get a torque twist when twisting the throttle or down shifting. This has always been the issue with BMW Boxer twins until the latest engine iteration in 2014 where the redesigned engine rotates the alternator and clutch counter to the flywheel, greatly reducing the torque effect.
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Originally Posted by Retired Army
