On part of my layout, I have 4 concentric ovals, in 1st, 2nd, 3rd and 4th Radius on an 8' x 4' board. I can run Class 05, Class 08, Class 15, Class 20, Class 37, Class 42, Class 47, Class 52, Class 58, Class 66, Class 70, Class 108 and Class 128 Diesels. Also I can run Flying Scotsman, Royal Scot and another Steam Loco LMS 2-6-4. In fact the only Loco I have not been able to run was a Duchess of Gloucester, which I sold. All of these run without any issues at all on my layout. I must emphasise though that I treat it as a Railway Layout, not a Scalextric Race circuit and my track is perfectly flat. I have never been able to understand the '2nd Radius and up only' caveat.