new to O scale trains

The ones called "traditional" or "postwar" are usually a compressed sized car designed to run on tight turns of 27"- 36" diameter (O27 - O36).  Generally a car that's shown as "40 ft." will be 10" overall ("40ft. boxcar").  "50" is 12- 12-1/2 in. long.  These are "traditional" sized cars.  As far as locomotives, the ones from origin (1950s- 1990's) are usually compressed, and run on those same track curves.

When you get to "Scale" and 1/48. those are the larger, longer, and taller cars.  If you want to run both steam and diesel, choosing the "transition period"- about 1945- 1959- allows for equipment you can mix "scale cars" with traditional in reasonable 40 ft.- 60 ft. (10"- 15"), and they look OK.

Steam engines after about 1930 were getting very large and scale models OF those later engines will not run on curves much smaller than 054.  So you end up with "compressed" engines, like the Lionel LionMaster line.   

A full scale passenger car is about 80 feet long- so an actual 20" in 1/48- those need wide turns, regardless of what the mfg. says they need to "run".  This mostly to look right without a lot of overhang.  So the manufacturers have made 15" and 16" passenger cars that look pretty good, and do not overhang too much- these will run on track as tight as O48.

Track: an O36 turn will need (with 3" on each side clearance) a 42" wide table, 048 (with 3" on each side clearance) a 50" table.  There are many plans designed for a 4' x 8 ft. table but you have to compromise on the engines, and the cars you plan to run.

Overall, in O Scale, for a layout in a normal sized basement or room, you have to make compromises.  Its still fun!!  To me, now, 2-rail track looks weird- and 3-rail to me looks "normal".  The reason to get into O Gauge is reliability, suitability to smaller hands, ease of working on the equipment with old eyes and hands, and far less "fiddly" track with fewer derailments. 

It takes some experience.  There is a lot of variety in O gauge trains.   Mike Wyatt gives a good outline.

Also 2 rail O scale usually means scale size with the smaller Kadee couplers attached to the body, not the bigger Lionel style ones that attach to the trucks usually.   And 2 rail scale engines are DC, not AC. 

Some people mix O gauge (track size) and O scale, the car size when they talk about the trains.   

I will add, to use the widest radius/diameter curves you can fit, at least on the outside loop.  This way you can run larger engines without worry.  I am stuck with a small 4x7 layout, so my outer loop is 042 so I can run my 1-700e reissue scale NYC Hudson on my layout.   My prewar Lionel OO trains fit my space better, but finding enough of the rare vintage track is a challenge in several ways.  But thats a whole nother ball game!   Welcome to O scale!   AD

Hi Spacely - glad your getting into a great hobby.  SCALE is the big consideration for any hobby. Lionel has been a great way to enjoy trains as a basic toy train layout hobby that started under that ole Christmas tree or moving onto a basic 4' x 8' sheet of plywood in the basement. Your inquiry of True O scale is 1:48 ! you can research online or go to your local hobby store and look into 'models' = they are specific on scale. Lionel started out designing an O = 027 scale that was short of its true idea's; closer to 1:50 scale. They were manufacturing for a family / youth for confined space. I suggest to keep O-scale & O27 separate for the viewing pleasure of that scale - if your expanding to larger or more involved trains - switching or yarding to check out this invaluable reference from the past that helped soooo many hobbyists : from "Classic Toy Trains = Track Plans for Toy Trains Paperbact" !  i suggest to save much time = think about your imagination and idea's of what kind of railroad plan & theme your interested in. railroads are serving many types of business & functions. you'll save yourself years of work if you can research early. many happy hours on your layout !

The history of scale in O Gauge railroading is a bit of a challenge to pick up. Prior to, say, 1990, we mostly had O27 Gauge and O Gauge. O27 was compressed to run on really tight 27" curves and use cheaper (shorter, less metal) track and switches. O Gauge was heavier (taller) track, still tight 31" curves, and better switches. Accessories were shared between the two. Very few engines and rolling stock were made to true 1:48 scale although some items were scale SIZED (just not in scale detail).

Since then, those two were consolidated into what's now known as Traditional when the industry began embracing true 1:48 scale in size and detail I think around 1990. The true scale offerings are more expensive and created a relatively new segment in the O Gauge market.

The challenge for us in the Traditional part of the market is dealing with sizes. They're all over the map and selectively compressed, not precisely 1:50 or 1:53. In fact, some Traditional items are darn near 1:48 scale in size

@Spacely71 posted:

... what are True O scale cars and how to tell the diff. when I buy more train cars? They look great buy them self, but make the rest of the cars look small.

There have been several good comments made already in this thread.  Keep these comments in mind, most specifically that almost all older stuff (pre-1990) is smaller, that much of the newer stuff is scale-sized, and that a small amount of older stuff is actually scale-sized too.

As to how to determine there are some hints:

With Lionel look for the Product Specifications box in each individual product's listing on the Lionel website.

For the larger scale sized stuff the key phrase to look for is "Standard O":

For the smaller stuff the key phrase you'll find here is "Traditional:"

This works most of the time, but not always, because the 'Gauge' entry is not always present, or sometimes a non-specific phrase has been entered here by Lionel instead.

For MTH look at the product number.  20- Series products are 'Premium' and largely scale-sized,  30- Series products are 'RailKing' and largely traditional sized.

Mike