I'll have a loop of O72 just to run it on, but that doesn't mean that I shouldn't play with my toys and see if it can go smaller. I do that with all my locomotives. My K-Line Big Boy is rated at O31 but it will run O27. I have a MTH DL-109 rated at O42 and it runs O36. The MTH PRR T-1 rated at O72 ran on my O48 loop, it didn't like it, but it did it. Will I run any of them regularly on the smaller curves, doubt it, but it's nice to know what they can take for the future since you can never know what's going to happen.