Track Help

Calculating Curve Tolerances

Written by Glenn. Posted in Track Help

This a javascript page which calculates the adjacent curves that you need in to avoid trains hitting each other going around the curve.

Note: It is set up for HO/OO gauge only.

All dimensions need to be in millimetres as for the pre filled wagon width and suggested straight track separation.


Longest Wagon
(Distance between the bogie centres)
Track Radius
Use the radio buttons to indicate where the radius
was measured from.

Wagon width  
Required Track Separation
(straight section, track centre to track centre)
ie, the amount the wagon hangs over the inside track
rail on the curve.
Adjacent Outer Track radius (track centre)  
Adjacent Inner Track radius (track centre)


This article was inspired by David's article on Curve Tolerances, and I was curious if it could be done mathematically.

Note: The calculations have not been tested in the real (model) world so please use with caution!


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