I am going to start building a train layout using Marklin K track. The layout will have parallel tracks and see that there’s a couple of radius’ to chose from. Which is the most common 2221/2231 vs 2241/2251? The layout will be 9’ x 16’ with 2 levels. Also which one is the normal spacing 57mm or 64.6?
The most common ones are the smaller 2221 and 2231 curves. But they are used more often because they take less space. On your larger layout You can try to use larger radii where possible. Clearly bigger is better, assuming you have the space for them. Trains look more natural on large radius curves.
For planning purposes, I would only use the 2210 curves when there is no space for the 2221’s.
The normal spacing is 64.6. The picture below may clarify the different radii.