It is determined by the geometry of the track you are using,
principally turnouts, but as others have indicated, it is around 3cm.
A word of advice: don't necessarily rely on a figure. When laying your
track, nothing substitutes for testing with extra large coaches such as
MKIII/IV's which have extra long overhangs, Centenary coaches which are
extra wide and locos with front overhands eg 4-4-0s. The idea is to
test with two such vehicles to ensure they do not collide. This of
course applies mainly to curves.
Graham Plowman, MROL Magazine
Thanks. However I am also interested in allowing space for the
coaches/locos that we haven't yet acquired. Given the dimensions and
pivot locations I can calculate the required space, but the Hornby
catalog doesn't give widths (or any dimensions at all in the case of the
Thomas range) so I wouldn't have known that some vehicles are unusually
wide. Our current stock has a maximum width of 37mm.
The movement envelope of our models is pretty consistent. The best way
to prepare your layout for models not yet purchased is to measure using
models which are on the extremes of size, for example:
- Lima/New Hornby MKIII for length, end overhang and centre overhang
- Airfix/Dapol Centenary/Auto Coach for width and centre overhang
- Lima GWR 45xx for height
If you do this, you won't go far wrong, but if you keep with the
geometry of the track you are using, you'll find that in general, all
of this has already been worked out for you.
The track centre to centre distance works out at about 45mm for straights
( 4mm = 1ft scale UK prototype). If you are using RTR standards you need to
go a little wider to allow for extra slop between the models and track. You
can get an idea of what you need by using the track centre chart on my web
page, which is for NSW HO. If you add 3mm to the result from the chart you
should be OK for UK 00 models.