Inquiring about 21" cars and minimum curves edges into a rather subjective realm.
Some folks want to run 21" cars on any curve where they will not derail regardless of appearance. Fine
Other folks prefer to not see the outside rail when a 21" car is on a curve. Also fine if you have the space.
I run all length passenger cars along with larger then normal curves however I find a string of my 18" passenger cars look best on my curves.
Even with curves on the small side I find the use of #7.5 or #8 switches look best with long cars. All subjective opinion.
