Looked at the NMRA standards for curved radii and find it a little confusing could anyone direct me to a good source that lists radii by types of rolling stock?
Did you look at the table form of the NMRA chart:
http://www.nmra.org/standards/s-8tables.html
It breaks down the Classes at the top, then has standards for each scale.
This Recommended Practice breaks it down further, and in one chart, maybe easier to digest.
What exactly are you looking for something like 40’ box car = xxx radius curves?
I don’t know that such a thing exists. You might be over analyzing this.
Model railroading equipment even of the same type is going to handle differently depening on how it was designed and manufactured. For example an old “standard” Rivarossi 80’ passenger car, straight out of the box, could negotiate 18" radius curves. This is because the trucks had off-set bolster mounts, the couplers were mounted on the trucks, and they left a really big gap between the cars. Take that same car and convert the trucks to pivot in the center, mount the couplers on the body so they couple closer together (to eliminate the air gap between cars), and then they have a difficult time negotiating anything less than a 36" curve. Other manufactures compromise and body mount the couplers but make it so they can swing a bit (Bachman’s big dome comes to mind). Flip one of your Superchief cars upside down and see how far back the Walthers people mounted the coupler pivot. Almost all the way back to the bolster.
There are other tricks too like making the wheels a little sloppier in the trucks, putting blind wheels in the center, extra wide wheel treads, etc.
And remember that even the broadest curves we use in MR are very tight by prototypical standards. The general rule is to use the biggest possible curves allowed by how much other things one wants to compromise for use of available space. I have an example of that too. Our club layout is shaped around an H shape. The Isle is the H and the layout surrounds it. Our room is almost the exact same size as a rather famous railroad called the “Cat Mountain and Santa Fe”. When I first saw the Cat Mountai
A short hand for HO would be 18" radius is for cars and diesels less than 60’, 24" for 60-70’ and 30" for 80’ .
Steam locos would be 18" - 6 driving wheels, 24" - 8 driving wheels, 36" the rest.
Keep in mind this is very rough and conservative. A lot of manufacturers make their bigger locos to go around 18" curves. Many long passenger cars use truck mounted couplers to get around 18" curves. And so forth. Even though a loco or car can get around a tight radius, operation and appearance are better with larger curves.
RP-11 referenced above can be confusing, but it is worth figuring out and using as guide.
Enjoy
Paul