Drafting Tutorial: How to Draw a Traditional Bicycle Frame.

Brandon Ives, July 22, 2004 (to be revised soon)

Little has been said about how to design, and more specifically, draw or draft a traditional double-diamond bicycle frame. In one of the early Rivendell Readers there was a stripped-down explanation of how to draft a basic frame layout. The only other step-by-step reference I can think of beyond that is in Richard P. Talbot's book, Designing And Building Your Own Frameset, which is now long out of print. Most "drawings" of bicycle frames are done on the computer in CAD programs of one kind or another. There are also some bicycle-specific programs, like Bicycle Forest's BikeCAD program. There's nothing wrong with using your computer, and most of my drawings will be transferred to CAD at some point.

Personally, I enjoy the labor of doing things the "old fashioned" way because it seems to allow me to get into the work more. Remember that I'm not a professional draftsman; I'm entirely self-taught and although I'm not much of a fine-artist I enjoy the process. I hope you also enjoy making your vision reality through this tutorial.

Whatever your reasons for wanting to draft your frame by hand, this guide should help you do it. I will present photographs with partial drawings that have each step marked in order with a corresponding number. These numbers will then be explained in the text following the drawing.

What you will need to complete this are a few simple tools, which I will discuss later. You'll also need all of your frame measurements as detailed as possible. If you only have a couple of things (like seat-tube and top-tube lengths and angles) you should read though this whole plan and note what other measurements you'll need. Make sure you have all your measurements listed center to center so that the starting line drawing is correct. Lastly, note that most of the measurements are given in metric, and if you need to convert to imperial, divide centimeters by 2.54 and millimeters by 25.4.

I would recommend reading all the way through this tutorial before starting your drawing.

Let's begin.

  1. The first line you need to draw is the wheelbase line-- it all starts here. I draw a line parallel to the bottom of the paper, between 10cm and 15cm above the edge. The distance depends on what your bottom-bracket drop is and 15cm will leave lots of room below the bottom-bracket (BB) drawing.
  2. This is your BB line and is measured using your BB drop. The BB drop is calculated by subtracting your BB height from your wheel radius. In this case 313mm (26'x 1.125" tire) - 260mm = 53mm drop. Now draw this line parallel to the wheelbase line.
  3. Now you get to actually start drawing your frame. On the BB line-- about 2/5ths along the line-- you should use your compass to draw a 35mm diameter circle to represent your inner BB shell diameter. This is where the ends of your tube miters should intersect with your BB in a lugged shell. If you're going to TIG weld or fillet-braze the frame, use the actual outer diameter of the BB shell you're going to use for your frame.
  4. The next major dimension you'll need is your chainstay length. This is measured from the center of your BB to the center of your axle. Draw a line the length of your chainstay length from the BB center point to intersect the wheelbase line. I draw a 10mm diameter circle at this intersection to represent the rear hub axle.
  5. Next, move back to the BB line and, measuring from the center point of the BB shell, draw a line along the BB line the same length as your cranks. At the end of this new line draw a 14mm circle to represent your pedal spindle. Lots of people leave this off their drawings but it is essential if you want to know about toe-clip overlap on the final design.
  6. The fun and frustration are about to begin. Now you need to draw your seat-tube (ST) center line. Using a protractor and long ruler draw a line from the center of your BB to the edge of your paper at the same angle as your ST angle. Make sure to measure the angle from the BB line as your base.
  7. Now make the first of two marks on your ST line. This mark is the top-tube (TT) center intersect. Assuming that you're using a level TT you can draw the line all the way forward to where the TT intersects with the head-tube (HT). If you are using some kind of sloping TT this horizontal line will be your 'virtual' TT line.
  8. The second mark you should make on the ST line is your seat height. This measures the location of the top of your saddle when the bike is built up. I use the LeMond method of calculating this: multiply your inseam x 0.883. This will be important to know when we draw in the stem later and need to know where the top of the saddle settles in relation to the stem height.
  9. These are the very basic tools I've used to draft this drawing: A pencil and eraser, compass, protractor, ruler, and yard/meter stick. Since I'm doing this in a small apartment in Belgium, I have my paper taped to a piece of cardboard and work with the drawing laying on the floor. Back home I have much better tools, but this simple set-up will get you though the drawing. I think the grand total was around $25 for everything.

Forward to step two!