Lionel list the Min curve of 54 for the SD 40 but I know that the SD 40-20 will handle O-36. Since the SD40-2 is longer is the 54 for SD 40 just for some cars or is O-54 accurate.
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Lionel’s SD40 is a recently tooled model and it features kinematic pilots which are attached to the frame, not the trucks. This bumps up the minimum curve requirement. The older tooling SD40-2 has standard O gauge pilots attached to the trucks which allow for tighter curves.
Thanks Woody based on your info I changed the order from a SD40 to a RS11.
I have a 2015 SD40-2. It’s minimum radius (according to the box) is 054. I see some of the newer versions listed as 036. Find the model number you want and look it up on lionel.com, they list the minimum curve in the text.
