As I understand it, it will depend on the radius of your tightest curve, and
the clearance of flangeways (on the points)
As you will be using Hornby set track, then the flangeways are going to be
pretty wide, so that shouldn't be an issue.
What will affect the setting is the radius of your tightest curve. Radius 1
is very tight, so will need a narrower gauge to allow reasonably free
running, so 14.2 would possibly be a good starting point.
If you're on radius 2, or even better radius 3, then 14.5 would be the
However, I stand to be corrected.
Prepare to becorrected. ;-)
Assuming that all the wheels of a model railway collection are not all
the same, (DMUs only?) then the correct dimension is from one flange
face to the opposite flange back. This is a bit difficult to measure in
a single operation with a pair of calipers. That dimension is however
15mm. The flange thickness _should be_ 0.5mm giving 1.0mm of play
between flange faces and rail heads at correct gauge.
So, if your flanges are 0.5mm thick (width) then the correct back to
back is 14.5mm
If your flanges are thicker than 0.5, which is quite likely, then you
need to reduce the 'back to back' measurement by an equal amount, but
not to a dimension less than 14.2mm.
However, if you are running "finescale" wheels and trackwork, whch you
almost certainly are not if you're asking the question then my answer
will be totally wrong and an argument of many eons and harsh words will
result. Whatever, my dimensions allow me to operate NEM, NMRA and
British wheels on the same tracks without problems.
PS - you will never get your wheelsets perfectly to gauge, but +/-0.1mm
of the above will be fine =8^)
For Hornby and Peco Set track 14.4mm is going to be to wide for many
wheels. Do what Greg suggested before and measure your wheel flange
thickness. As you have calipers you can measure the check face to check
face dimension of the set track. For older models with deep fat flanges
a minimum wheel back to back dimension of 14.00mm should work for set
track. However before accepting these numbers see my web page for a XL
spread sheet that does the sums for track standards. Measure your set
track check face to check face dimension, Use a check gauge of 15.0mm
for set track. Get the track numbers to be close to your measured track
numbers then you can play around with your back to back dimensions to
get the best values. I must stress these numbers are for Peco and
Hornby set track only and are not suitable for the other Peco turnouts.
HO wagon weight and locomotive tractive effort estimates
DC control circuit diagrams
HO scale track and wheel standards
Any scale track standard and wheel spread sheet