Minimum curve radius for N scale steam locos

[liquidcross]

I guess this would apply to diesels, too, but steam locos are generally longer. Anyways, what's the minium curve radius I can have so that a steam loco won't derail? I'm not going to push my luck with a monster 4-8-8-4 loco, obviously; I'm thinking more along the lines of 2-8-0's and such.