Smallest prototypical curve in HO?

[Will_Annand]

The Credit Valley had curves in its narrow gauge days that were on the order of 700' radii, and these were described in print as "tight". That works out to about 10' / 120" radius in HO...!

But transit curves are probably the tightest prototypical. Out at the Halton County Radial Railway museum, they have a turning loop that can't be more than 60 or 70 foot radius - that's under 10" in HO.

Andrew

Andrew, I hope you are refering to the region when you mention the Credit Valley's marrow gauge days.
The Hamilton and Northwestern Railway, as well as the TG&B were narrow gauge.

The Credit Valley Railway itself started life as the first standard gauge railway in ONtario.