Bike Fit

“Just as the ideal of classic Greek culture was the most perfect harmony of mind and body, so a human and a bicycle are the perfect synthesis of body and machine.”~Richard Ballantine

Measure your inseam first”
• There is no “one-size-fits-all” when it comes to bike fit. Fashion should be left out of the equation entirely.
• Especially for long-distance cycling, comfort is the first consideration.
• In the same way a “bike fit calculator” might estimate, the information on this page will give most people a good starting point in the search for a comfortable and efficient riding position.
• In the end, however, theory and formulae should take a back saddle to real world experimentation and refinement.

Choosing a frame

Ideally, bicycle frames are designed according to intended use. For instance, the geometry of a diamond frame randonneur bike will feature longer chain stays than a racing machine, to lengthen wheelbase and fit bigger tires.

How do you determine correct frame size?

Frame “height” (seat tube)

A few physical dimensions are in order, beginning with what is commonly referred to as “inseam,” but has little to do with what a tailor measures. We are interested in the full measurement from floor to pubic bone. You can do this at home with just a pencil and a large, hardcover book.

You might recruit a friend to wield the pencil, while you snug the spine of the book into your perineum with about the same pressure as sitting on a saddle. Stand with bare feet, six inches apart, using the book like a set square, with leading edge against the wall. Have your assistant mark the wall at the top of the book spine.

Measure from floor to the mark on wall. Repeat a few times and average results.

This is the measurement corresponding to what some bicycle companies refer to as “standover height.”

You want about 25mm clearance above the top tube of a road bike. If the frame has a sloping top tube (common on “compact” frames) consider this the desired clearance at mid-point. Choosing a frame smaller than this will create problems down the road, if higher handlebar position is desired.

Top Tube

Appropriate top tube length—seat tube to head tube—is somewhat more difficult to ascertain. Unless you are going custom, most off-the-peg frames will have a top tube corresponding to the seat tube. That is, if the seat tube is 56 cm, the top tube will also be around 56 cm. Dialling-in fit will be achieved via different-sized handlebar stems. Stock frames will fit the majority of evenly-proportioned people.

Don’t be confused by top-tube lengths given as “effective.” This is the length of a sloping top tube, measured as if it were level. Accordingly, a rearward sloping top tube measurement will intersect with the seat post on a level axis.

Correct top tube length can be estimated by combining trunk and arm length. Measure trunk length sitting upright with your back against a wall, from floor to the top of your shoulder. Forearm length is measured from the elbow to the centre of your clenched fist (hold a pencil and measure to the lead). Total arm length is measured from shoulder to pencil. Use the equation: top tube length = 75.25% trunk length + 7.8% forearm length + 7% total arm length – 1cm (½”). Round to the nearest ½cm.

Adjustments

Once we have a frame that is basically the correct size, it’s time to get down to fitting. We work on optimizing biomechanical and ergonomic position.

Saddle

Saddle height is the most basic and important setting to achieve biomechanical efficiency and comfort. Use your inseam measurement to estimate correct saddle height.

The formula: inseam (cm) x .883 will return a good starting point, representing distance between bottom bracket spindle centre and top of the saddle. Legs should end up with a 30 degree bend at 6 O’clock position. Another ballpark fit can be had by setting saddle height so the leg is straight—hips level—with heel on the pedal, at 6 O’clock. This should result in similar bend in the leg, when the metatarsal, or ball of the foot, is moved to its normal pedalling position, with the ball of the foot centred roughly over the pedal axle. The optimum position allows full pedal stroke without rocking the hips.

The saddle can also be adjusted forwards and backwards, on its rails, which pass through the seatpost clamp. Adjustments here will ideally be made to dial in pedalling position, rather than saddle-to-handlebar distance—hence the importance of top tube/stem length.

Handlebars

Handlebar width should be based on shoulder width. The trend towards wider bars, to “open up the chest,” compromises comfort as the body sags between splayed arms.

Modern bicycle construction mostly uses a “threadless” steerer on the fork, which passes through the headtube and headset. The handlebar stem is clamped to the steering tube above the headset.

Handlebar height and horizontal distance from saddle is modified by changing the handlebar stem and/or height. Commonly, “threadless” stems range from 40 to 120 mm. Hinged, adjustable stems are also available.

 

 

 

 

 

 

 

 

Difficulties occur when the fork steerer on a threadless system has been cut very close to the top of the head tube, either at the factory or during assembly at the shop. This simplifies assembly and sales in the short term, but restricts positioning for the user.

An uncut steerer allows wide latitude for handlebar height, without recourse to a riser stem or unsightly steerer extender—the only remedy for a too-short threadless steerer.

The illustration above (right) shows an exceptionally long, uncut steerer, piled with spacers above and below the stem. This allows great latitude in positions to test, before the steerer is finally cut to length and excess spacers removed. Spacers are simply juggled under or over the stem to achieve different heights.

Keep in mind that bar position moves backwards or forwards as the steering column rises and falls, in concert with the headtube angle.

Generally, we should be looking to balance weight equally between the hands and behind. An equilateral triangle is the most stable geometrical foundation. Cockpit length should enable a comfortable bend in the arm.

The final position will be determined by a combination of factors, including intended use—touring, commuting, randonneuring, racing—and personal physical dictates. Again, comfort should be the basis for the final decision.

The traditional 1-inch quill stem*—all but eclipsed now by the newer 1 ⅛” threadless system—can be raised simply by loosening an internal binder bolt and raising the column inside the steerer tube. Hence steerer length does not influence the final bar position.

Luckily (for owners of bikes with threaded steerers), there is still a choice of quality quills, including the popular, finely finished Nitto Technomic Deluxe, with 190mm column height, 11 cm of which can be exposed above the headset. It’s humble cousin, the plain Technomic, allows a towering 16 cm.

Like their bolt-on descendants, quill stems also come in a variety of sizes, to dial in cockpit length. *Quill stems are also available in 1 ⅛”. Make sure you have the right size for your steerer.

Pedals

At the foot/pedal interface, many recommend KOPS, or “knee-over-pedal-spindle.” With the foot at three O’clock, drop a plumb line from below the knee patella and adjust the saddle fore/aft on its rails until the bob intersects the pedal spindle.

Other variables, of course, are the chosen position of the metatarsal in relation to the pedal spindle and the angle of the seat tube and length of crank (see below).

While it may be a good starting position, don’t worry if other considerations suggest a breach of the so-called KOPS ideal. Find a position that gets the saddle under your ischial tuberosities, or sit bones, allows you to shift further back to enhance seated climbing and further forward, when hammering “on the rivet.” If that doesn’t equal the KOPS canard, so be it. It’s more important to be balanced on the bike in all riding positions. If a more rearward seated position is required than saddle rail length allows, a curved “setback” seatpost may be used.

If you want to adjust the pedaling circle, you might consider using different length cranks. Again, such calculations shouldn’t be taken as gospel. Experiment by all means, but take these ideas with a grain of salt. Many shorter or taller riders prefer crank lengths that following someone else’s theory to the letter would preclude.

Most cyclists who ride more than short distances will choose some system to position and attach feet on the pedal. Today, this will most often mean a “clipless” system, with varying degrees of “float,” allowing lateral movement of the heel. The majority of riders will also benefit from modifying the angle of the foot on the pedal with wedges under the cleat and/or insoles. This corrects varus (inward) or valgus (outward) angle of the foot and often solves stubborn knee issues. To account for hip width, cleats may also be repositioned laterally on the shoe, closer or further from the crank, to adjust “Q” factor—the distance between feet.

As mentioned above, the decision on where to place the metatarsal in relation to the pedal spindle will depend on a number of other variables. Many distance riders are finding that a more forward foot/rearward cleat position is preferable.

Conclusion

The bicycle is a wonderful 19th century experiment in cybernetics that today still requires the same cooperation of human and machine to perform efficiently. Ultimately, no one else can fit you to your bike. You must first listen to the feedback your body is sending and become familiar with its language.

Rather than “fitting machines” and programs based on some formulaic “ideal,” find a bicycle fitter who will help interpret your individual needs, using practical expertise and your personal feedback to help dial-in your fit.

A good fitter will have you describe the messages your contact points and sinews are sending while pedaling under stress, then adjusting the bike to optimize comfort and biomechanical efficiency. In other words, the bike should be fitted to you, rather than the other way around.

Adjustments may also include training recommendations to balance weak links in the “engine.”

Make all changes incrementally (5 mm at most). Do not make gross alterations before an important event.

All orthodoxy is secondary to comfort. We do not ride to endure discomfort. Ideally, we maximize comfort so that we can get our masochist fix somewhere else—say, on a 600 kilometre marathon ride!