Thoughts about bogie design

[bikkuri bahn]

The controversy over the London Thameslink bidding, with Siemens being the preferred bidder, got me interested in the type of rolling stock that will be used.  Apparently a variation of their Desiro series will be used, but fitted with SF7000 bogies which is an inside bearing design.  Bogies are a facet of rolling stock engineering I find fascinating, and I found the selection of inside bearing types interesting, as they are rare in Japan.  I have always wondered why they are so popular in Europe, a situation which is the opposite in Japan.  While searching the net, I came across this:

http://www.jreast.co.jp/e/development/tech/pdf_1/33_37tecrev.pdf

An interesting though ultimately not very conclusive report of cooperative bogie design.  Note that the DB team constructed an inside bearing design, while JR East stuck with outside bearings.  The report notes that inside bearing designs are inherently light and compact.

 

So why are inside bearing bogies popular in Europe but not in Japan? Here are my guesses:

Their compact size allow for lower floors, useful in European operational practice of low platform passenger loading.  Also, in the UK, though it has high platform loading, with its restrictive loading gauge, a compact bogie allows more room on the underframe for equipment, more room for sound insulation and possibly slightly larger passenger space.  On the other hand, in Japan, the loading gauge is more generous than the UK and close to the European.  Underfloor space is more plentiful, and the advantage of inside bearing bogies is offset by the decreased ease of maintenance compared with having bearings on the outside.