New vs. Old Vibration
Just picked up an old (1989/90) Schwinn 754 for very cheap.... needed some tweaks and updating, but a good ride. Compared to my 2021 Giant Contend AR, it's almost night and day smoother with much less vibration, with equal size tires and psi (25c/90ish). Both bikes are aluminum, Schwinn with a steel fork, Giant with carbon. Schwinn is several pounds heavier, but not looking to keep weight down, just a better ride.
With all the marvels of modern carbon, engineering, light and aero, etc. (so we're 'told')-- am I missing something? The Giant feels and sounds like a rattle trap compared to the Schwinn.