This is my first attempt at using a forum, so please forgive if I do anything wrong!
I am in the process of converting the wheel sets on my n-scale rolling stock from plastic to metal. In addition to the choice of suppliers of n-scale metal wheels (Atlas, Intermountain, etc.), I noticed there are 2 different sizes of wheels, 33" and 36", as well as wide or narrow tread width. Could someone be so kind as to enlighten me as to what size wheels fit which particular freight cars, as there must be a reason for having two different sizes available? I read somewhere that wheel size depends on the truck weight, but I am not sure if this applies to n-scale. Advice would be most appreciated.
Wheel sizes are selected due to several considerations:
Freight Cars - 33" wheels are used on cars with a capacity of 77 tons or under. Most older 50/60’s era cars use this wheel. The larger cars(like 3 bay covered hoppers with 100+ ton capacity) use the 36" wheels. So basically if you have a car with over 77 ton capacity(those small CAPY numbers on the side), it will use the larger 36" wheels.
Passenger Cars - Most passenger cars use 36" wheels.
Now - on to the tread width. The standard NMRA wheel tread is designed to work on virtually all N scale trackage manufactured, The more scale looking ‘narrow’ tread is popular with the folks who also like the code 55 trackage that is available from several manufacturers.