I have noticed several comments about 387s poor ride and excessive lateral movements over points, but on a few recent rides I have noticed something else: 'hunting' on plain track at speed. This is something I've rarely encountered since the days of loco hauled Mark 1s with BR1 bogies on the Portsmouth - Cardiff services in the 1980s and more generally the old Diesel Mechanical 'heritage' DMUs.
Those Mark 1s that survived longer tended to have either Commonwealth bogies or B4 / B5 bogies, especially EMUs and catering vehicles - which both were much less susceptible to hunting. They were permitted to go 100 mph rather than 90 mph as was the case with BR1 bogies. I don't recall any ride issues with the longer lived EMUs with Gresley bogies (such as 304s and 308s) either.
Hunting is rare now and many of the younger readers on this forum may not have heard the term. It refers to a high frequency sideways (that is lateral) oscillation of the bogie. I am no engineer and so can't describe the precise set of causes, but I believe that additional 'yaw' damping has often been used to prevent excessive hunting. Wikipedia has a fairly detailed article (with lots of scary equations!): https://en.wikipedia.org/wiki/Hunting_oscillation. Please correct me if my 'layman's' definition isn't really correct though!
i always put this down to when they accelerate because they do speed up quite quickly, thye always feel like they are going to slip. Definately have a "swinging" like motion when makes them pretty bad over points at speed and awful if you have a bad back.
Better seating would be an improvement.