Clive D. W. Feather wrote:

D stock isn't any wider than C stock; it's limited where it can go
because:
* some stations (like Bayswater) can't fit 6*D though they can fit
6*C;
* the suspension has been stiffened and it's therefore only allowed
on track maintained appropriately (which, off-Line, means Acton
Town to Northfields Depot).

LOL! You can't have travelled on the District for several years if you
think that D-stock can only run on track that has been "maintained
appropriately".

Seriously, Tube Prune's website* says "The poor quality of LU track has
led to cracking in the bogie frames and some derailments due to the
stiffness of the frame. The D Stock bogies are being replaced by new
bogies similar to those supplied by Adtranz for the new Northern Line
1995 Tube Stock. These bogies have flexible frames designed to overcome
the dreadful state of LU trackwork." That page was last updated a year
ago, so maybe the bogie changes are now complete. Can anyone confirm
this?

* http://www.trainweb.org/tubeprune/Rolling%20Stock.htm

--
Richard J.
(to e-mail me, swap uk and yon in address)