steam loco question

[nw-mailing-list at nwhs.org]

In a nutshell, the tyres on the wheels are slightly coned - increasing in 
size towards the flange. Thus, as the loco moves to the outside of a curve 
the outside wheel is riding on a slightly larger diameter part of its tyre - 
and the inside one is on the smaller diameter on the outside of its tyre.

I'm sure that there's a more technical explanation than that, but that's it 
really!

Very best wishes,
Peter Prydderch  Stockport  UK