No more than 20 years ago racing frames were lugged steel, built by craftsmen. Many aspects of design like the diameter of the tubes for example had not changed for 100 years. Frames were built in one centimeter increments so there were as many as 18 different size frames to cover the complete range of different size people.
Top tubes on road bicycle frames were horizontal and exactly level. This gave a point of reference, and once a rider had determined his correct size frame, for the rest of his life he could then buy any brand of frame in his particular size, and it would fit.
No one ever talked about handlebar drop, (The distance from the top of the saddle to the top of the handlebars.) because if a person had the correct size frame and the saddle was set for their particular setting, then the height of the handlebars above the frame was automatically correct. It was limited by the amount of adjustment in the old quill stems. About 1 1/2 inches. (37mm.)
In the mid 1990s this changed mainly due to the influence of mountain bike design and road bike frames are now labeled “Compact,” which means they come in fewer sizes, and the greater differences between small, medium, and large are taken up by longer seat posts, and a variety of handlebar stems that come in different lengths and angles.
Choosing a frame size is the easy part because there are fewer sizes, but where do the handlebars and saddle go in relation to everything else? One answer is to find your virtual frame size and create an imaginary horizontal line that becomes a reference point, and the handlebars are then set a certain distance from that reference point.
Different manufacturers’ sizes will vary slightly, and once a person has decided on a particular brand, they should go by that companies recommended size. Generally speaking an XS frame will fit a person 5’0” to 5’4” tall. Small frame 5’3’’ to 5’7” tall. Medium frame 5’6” to 5’11” tall. Large frame 5’10” to 6’3” tall. And a XL frame 6’2” to 6’5” tall.
There is some overlap in sizes, notice that a person 5’10” tall could use either a medium or large frame. This person should choose the smaller medium size for racing, or the large for more leisurely riding. The larger frame will have a longer head tube, making the handlebars higher in relation to the saddle height.
For some time now people have been asking where they can find my frame sizing chart that used to be on my old website. I have posted a printable version as a PDF, you can find it here. Instructions are on the sheet, your virtual frame size will be in the “Center to Top” column, as it represents the top side the top tube on an of the old school level top tube frame.
For example, if the virtual frame size is 61cm. measure that distance from the center of the bottom bracket, and mark the seat post at that point with a piece of masking tape. The top of the handle bars should be between 9 and 12.5cm above the horizontal virtual line. An easy way to check this, on a level floor, measure vertically down to the floor from the piece of tape. Add the 9 to 12.5 cm then measure up from the floor to the top of the bars.
The chart was originally intended for a racing set up, and one thing to keep in mind is that modern handlebars are flat on top and the brake lever hoods are higher. There is an article here on saddle height, that some have found useful.
The frame size chart also has top tube length and stem length. If you take these from the same line as your virtual frame size, and add the two together, you will have the recommended distance from the center of the seat post to the center of the handlebars. Measured horizontally across. (You can ignore the 1/2 centimeters.)
No frame sizing method or chart is written in stone, it is intended as a guide to give a person a place to start from. There will probably need to be some fine tuning to arrive at the perfect position. However, for someone starting out, if you know your virtual size before you buy a bike, you will be more informed and have an idea if the bike you are considering is at least close to the right size.