Why Royal Enfield Classic 350 vibration level is high?
Royal Enfield uses an older engine design that utilizes a large single cylinder. These are often called thumpers as they deliver all of their power in a rhythmic cycle that results in the vibration.
As you add more cylinders it's easier to smooth out the power delivery as you can stagger the sequence that the cylinders fire in. They never fire all at once. Most sports bikes use an inline four engine. These have 4 cylinders that fire in a staggered sequence, usually at higher RPMs, that has a much smoother power delivery with almost no detectable vibration.
As a result sports bikes tend to have a whine/scream rather than the rhythmic sound that you get out of single cylinder.
Questions about Royal Enfield Classic