I’ve been reading The Complete Book of Long-Distance Cycling by Edmund R. Burke, Ph.D. and Ed Pavelka. If you’re interested in LD riding, (i.e. more than 60 miles/100 km or so), this book has lots of advice. Some of it is pretty obvious, such as “drink water while riding”, but it’s all good to know.
One place where the book is a little scattered is the chapter on fitting a bike to the rider (chapter 3). There are 16 suggestions for sizing a road and/or touring bike, but they jump around between riding positions and component sizing in a seemingly random order. In fact, the most basic measurement (bicycle frame size) is the very last item mentioned. What’s up with that?!? I sifted the size/fitting suggestions from all the technique/posture tips, then I put the component suggestions in an order that made some sense to me. (I omitted information on custom-built frames, e.g. top tube length, as this isn’t financially realistic for me.) I use (fit #n) below to refer to the original fitting number scheme in The Complete Book of Long-Distance Cycling. Be sure to check the book for more advice, nuances, and trade-offs in fitting your road bike! Keep in mind that these are for long-distance cycling with a road/touring bike. If you’re riding for speed or you’re on a “mountain” bike, these may not be appropriate.
The first body measurement you need to know is, how long are your legs? To find this, stand in front of a wall with your feet about 6″/15 cm apart. Use a large hardback book to simulate a saddle. Put it square against the wall and slide it up (gently!) until it’s pushing firmly against your crotch. Mark the wall at this height and measure to the floor. This is your “inseam length”.
- Multiply your inseam length by 0.67 to determine your frame size, from the center of the top tube to the center of the crank, along the seat tube. (Fit #16)
- Multiply your inseam length by 0.883 to get the saddle height, the distance along the seat tube from the center of the crank to the top of the saddle. (Fit #10)
- Use your inseam length to determine the proper crankarm length (fit #15):
Inseam length Crankarm length <29″ 165 mm 29-32″ 170 mm 33-34″ 172.5 mm >34″ 175 mm
That’s it for the math! Now that the basic frame components are set, we can move on to slightly more subjective measurements.
Shoes, cleats, toe clips: See (fit #14). It’s almost a page long, and all of it’s very important to people (like me) with knee problems. (It can also affect saddle adjustment, below.)
Saddle adjustments: The saddle should be level (fit #11). Sit in the center of the saddle and backpeddle until the cranks are horizontal. Slide the saddle front/back so that a plumb line from the forward knee touches the end of the crank. (Fit #12)
Your handlebars (drop bars) should be as wide as your shoulders or even a little wider, (fit #5). Position the brake levers per (fit #6) and your personal preferences.
Stem adjustments: Try setting the stem height about 1″ lower than the saddle–if you cannot comfortably stay in “the drops” for several minutes, raise the stem until you are comfortable. As you gain flexibility and strength, lower the stem for a more aerodynamic position, (fit #7). A good guess for stem length (a fixed component, not an adjustment) can be derived by sitting in the saddle, grasping the brake hoods, and bending the elbows slightly (as if riding). Now look at the front hub–it should be slightly (or completely) obscured by the handlebars. If it’s not, try a longer or shorter stem (fit #8).
For completeness, (fit #1-4, 9, 13) have more to do with riding position and technique than fitting a bike, IMHO.