Frame size numbers are often cited but rarely verified on vintage three speed bikes. Let's take a look at a few examples of quoted versus actual frame sizing.
What is Frame Sizing?
The most basic measure of frame sizing for vintage three speed bikes is the frame height. The frame height is measured from the center of the bottom bracket opening to the top of the seat tube (not the seat post, the seat tube). If the cranks are in the bike, you can get reasonably close by starting at the center of the crank spindle/axle and going to the top of the seat tube.
There are other measurements relevant to frames (reach, chain stay length, etc.), but vintage bikes were sized by height in inches. This differs from today's production practice of sizing frames like t-shirts (s, m, l, etc.), and differs from custom bike measurements where every dimension of the frame is checked and made-to-order like a custom business suit (perhaps I am dating myself - how often do men wear business suits anymore?).
So let's apply the traditional height measurement to a few common Schwinn and Raleigh frames to see how close they actually are to the stated sizes. I don't own any very small frames, so everything will be standard size or tall size frames.
Raleigh
Raleigh's commonly stated frame sizes for the 26-inch wheel three speeds vary based on model. The usual "Sports" model and the "Superbe Sports", and similar bikes, are usually stated as 21 inches and 23 inches in size.
My experience is that Raleighs run "true to size". Here are a few examples.
Above, a 1958 Raleigh Sports shows almost exactly 23 inches tall. This frame is very close to the stated frame size in the catalogs and as commonly quoted online.
What about some other models? Look at the 1953 Raleigh Lenton frame above. Again, very close to the quoted size of 23 inches.
Are they all 21 or 23 inches? No - some models are different. Look at the 1949 Raleigh Clubman above. For part of its life, the Clubman came in an "intermediate" size of 22 inches. Raleigh was splitting the difference between the standard 21-inch frame and the tall 23-inch. Measuring this 1949 Clubman, it's close to the stated 22 inches tall. Again, it runs basically true to size.
Schwinn
There are three common men's (diamond) frame sizes given in the catalogs for production Schwinn three speed bikes with the usual 26 inch wheels: 19 inches, 21 inches, and 23 inches. Schwinn copied the English model of sizing the frames in that regard. I don't own any 19-inch frames, but I've owned plenty of 21-inch frames, and a few 23-inch frames.
Pre-war bikes: The actual frame sizes of pre-war Schwinn three speed bikes is close to the stated sizes in the catalogs. Let's take a look at a good (and unusual) example: a tall frame Schwinn New World. The above pre-war New World frame is almost dead-on the 23-inch mark. It runs "true to size", as they say. The same is true of the 21-inch frame pre-war New Worlds: they run "true to size". I've owned several and they call came in almost dead-on at 21 inches.
Post-war bikes: Starting in the 1940s, Schwinn began to change the way it produced common three speed bikes, Such as the New World. Construction went from a fillet brazed frame to a welded frame with a few fillet brazed joints in areas the welding equipment couldn't handle. As time went on, more and more joints on the frames were welded. Let's take a look
Above is a 1950 Schwinn Superior. The early post-war Superior was a welded frame bike primarily, with a few brazed joints in spots the welding equipment could not get. Despite being listed as a 21-inch frame, the actual size is closer to 22 inches. It's right around 21+3/4 inches. My 1947 New World is almost exactly the same - slightly under 22 inches.
What about a tall frame? Let's take a look at a 1959 Schwinn Traveler as our example. This frame is stated to be 23 inches, yet the actual measurement is much closer to 24 inches. Again, the frame runs a bit larger than is commonly stated, and larger than what the catalogs state. My 1964 and 1957 tall frame Travelers also run closer to 24 inches than to the stated 23 inches.
What about fillet brazed Schwinns, like the 1940s-50s Continentals? They also run somewhat larger than the stated size. They were alleged 21-inch and 23-inch frames, yet this 1947 Continental frame is closer to 22 inches. In that sense, it's like the post-war New World and the post-war Superior in running a little large.
Conclusion
Don't necessarily take the stated frame size in the catalog or online as gospel. Some frames, such as post-war Schwinn frames tend to run a bit larger than stated. Other frames, such as the Raleigh run true-to-size. Like a pair of shoes or an off-the-rack suit, the stated size is a number that gives you an idea of what you're dealing with, but it's not always dead-on for what the final size will be.
In terms of common, production three speed bikes, pre-war Schwinns tend to run true-to-size. Post-war Schwinns tend to run a bit larger than stated size. Raleighs tend to run true-to-size.
One thing I am often asked is, "how can you tell what size a frame is just by looking at it?". I look mainly at the head tube and the distance between the top tube and down tube. This works for both English and American three speeds.
Additionally on post-war Schwinns, you often can look at where the seat stay meets the seat tube. Often on tall frames, the chain stays double-connted to the seat tube and top tube, crossing lower on the seat tube. This is not true of all Schwinns, but it can be a helpful tool for the common ones from the late 1950s and onward.
Above, look closely at the head tubes of the two bikes. Notice how the green bike has a much larger gap between where the top tube meets the head tube and where the down tube meets the head tube. After you see these gaps enough times, you'll be able to "ballpark" frame sizes. However, your eyes or the camera can be misleading sometimes, so always check if you are not sure.