Bruce wrote:
On Thu, 13 Aug 2009 12:22:13 +0100, "Recliner"
wrote:

The ever-reliable Wiki source says that the 2009 stock is 2.68m wide
and the 1973 stock 2.629, so the 2009 stock is apparently 5cm or 2"
wider. It also says that, "Unlike the 1967 Tube Stock, the trains
are built 40 millimetres (1.6 in) wider to take advantage of the
Victoria line's slightly larger than normal loading gauge compared
to the other deep level tube lines."

Ironically, one of the reasons why the Victoria Line tunnel was built
to a larger diameter was to reduce air resistance. ;-)

It's not unreasonable to build the first stock for the line small to reduce
air resistance, and then build subsequent stock large to push the hot air
along.