... D stock could be quite bouncy ...
It's been a long time since I last rode the Underground,
and even longer since I travelled on D stock, but I'd
attribute the bumpiness of the ride less to the trains,
but more to the track. I mean, it is very, very busy and
therefore wears out rather quickly, in particular around
points. Also, the D stock is lighter than the A and C stock.
Perhaps, with the added weight due to the new components,
and the less demanding timetables on overland routes, the
rebuilt trains will run more smoothly.