I would like to add one more contribution into the fray. Some list members have contacted me off list for a clarification on how to measure the Q factor on their bikes and more importantly how to measure the Q of their bodies.
For me let me first specify that I do not measure the Q from outside crank edge to outside crank edge. For me this measurement has no value other than to compare one crank to another. Instead I measure the Q that most closely relates to our bodies. You must first clip, snap or otherwise secure a shoe into your pedal (without your foot in it). Measure the distance from the middle of the shoe to the center of the downtube when the pedal is closest to the downtube (at 2 O'clock when facing the crank side.) You can then measure the other pedal side and add the two measurements together or just double the crank side measurement for an approximate total tread width.
Next you need to measure the Q of your body. For this you need to stand up with hands placed in macho fashion on your hips, with the thumbs to the rear and your fingers to the front. Feel for the very tops of your illia crest (otherwise known as the crest of the hips). Now lie down on a hard surface face up and once again feel for the top of these crests. Assuming you have no paunch you can take a straight edge ruler and measure the width from one crest to another. This measurement almost exactly corresponds to the width of your femurs as they exit your hips. My narrow hips measure 10 inches but my wife, who is not big boned measures 10.5 inches. Most men measure 10.5 or larger. Most narrow Q factor bikes that I have seen measure about 10 inches which means that for optimum bone on bone alignment the smallest Q factor cranks are too small for most riders. This was just borne out by a list member who submitted a recollection of his observations of most riders on quill pedals, It is the outside nub not the inside nub of the pedal which is the limiting stop which holds the shoe on the pedal. Clearly our bodies are telling us something different from what the industry hype is calling for.
To sum up, for optimum efficiency the femurs need to exit the body and drop straight down from their attachments to the hips. If your pedals are in too narrow for your hips, you muscular efforts are in conflict with the bike. Narrow Q is hype. Q needs to match you in order for the bike to be a perfect extension of your body.
Garth Libre in Miami Fl USA