In Issue 147 we spoke in-depth about crankarm length and how crankarms that are too long can cause knee pain. In this article we will be concentrating on pedal stance width and why this is important, and how it’s related to pain. We will focus more on the pedal stance width of road bikes and tri/TT bikes because they have similar bottom bracket shell widths and cranks, with Q-factors right around 146mm. Mountain Bikes on the other hand offer different crank widths (Q-factor) such as 158mm, 168mm, 175mm, 176mm, and even wider.
Pedal Width vs. Stance Width vs. Q-Factor
Let’s define several terms: pedal width vs. (pedal) stance width vs. Q-Factor. These terms are often used interchangeably but really have different meanings. Following is their applicable (cycling) definition:
- Pedal width – The distance from the center of the pedal to the outside of the closest crankarm. Standard road pedal width is 53mm.
- Stance width (or pedal stance width) – is the distance between the center of one pedal to the center of the other pedal.
- Q-Factor – (or quack-factor which is a reference to the wide stance and waddling gait of a duck) is the distance between the outside of one crankarm to the outside of the other crankarm measured at the points of the threaded portion where the pedal axle attaches.
The Knee Bone Is Connected To the Ankle Bone…
There are 3 points for each leg that ‘pivot’ while pedaling:
- Femoral head/GT – You can’t see or feel the femoral head leg, but the greater trochanter (GT) is the next best thing. The GT is the boney protrusion that you feel below the top of your hip, the iliac crest, and is positioned so that it accurately represents the top pivot point.
- Knee – Simply defined, the knee divides the femur and the tibia/fibula and is the joint that allows the leg to bend. To find this pivot point, locate the bottom of the patella and move laterally to the outside center of the knee. This will be very close to the pivot point.
- Ankle – The easiest pivot point to locate. Just look for the malleolus, or the protruding round bone commonly referred to as the ankle bone.
While pedaling, you want all of these pivot points aligned so that you are pushing straight down. Any angling will not only rob power, but will place torque on your knees in a direction that is not natural (often resulting in knee damage or minimally, knee pain). Remember, cycling is an accumulation of micro-injuries and, if you want to continue cycling pain-free into your sixties, seventies, and even eighties, it is essential to take care of yourself now.
Bike Fitting Failures
Americans have historically had trouble with pedal stance when riding on road bikes. The culprit in this is the bottom bracket shell on these types of bikes –they’re too narrow for Americans. The Europeans, however, are generally thinner and more narrow, lighter, shorter, and smaller than us wider-hip American. When we lock our feet in a too narrow stance as we pedal, the knees have no other option than to oscillate (go out at the top of the pedal stroke and in at the bottom of the pedal stroke).
On the other hand, bottom brackets and cranks on mountain bikes are designed and built with a larger Q-factor than road bikes, placing most MTB riders with the correct pedal stance. You will know if your pedal stance (usually determined more by Q-factor) is too wide. If so, your knees will start diving inward at the top of the pedal stroke and you might experience pain as well.
Two bicyclists came in recently, both having the same issue (knees going out at the top of the pedal stroke) and both were now complaining of newly developed knee pain. Both happened to have been fit by the same persom at the same bike shop, and both were fit wrong. There are several ways to correct this issue, but most create more long-term knee pain.
In the case of these two bicyclists who came to me with knee pain, both were due to incorrect placement of wedges between the cleat and shoe. The idea behind cleat wedges consists of placing the thicker side of the wedge along the outside of the shoe, resulting in a canting of the knee inward at the top of the stroke. It can also be done with the thicker portion of the wedge reversed to cantilver the knee outward.
Although the fitter got these bicyclists knees to track straight, he introduced tremendous knee pain for these bicyclists, forcing them to stop riding for a couple weeks. In both these scenarios, the fitter is artificially forcing the rider’s knee into a position it doesn’t naturally want to be in.
The only correct way to get the knees to track straight(er) is to widen the pedal stance, not cantilver the knee using wedges. This can be accomplished in several ways including:
- Pedal Washers (2-4mm total) – Add up to 2 x 1mm pedal washers each pedal. Be cautious since adding more may not allow enough pedal thread engagement with the crank-arms.
- Pedal extenders (40-80mm total) – Adding a pedal extender to each pedal provides a solution for unique circumstances that require considerable width additions.
- Speedplay Pedal Spindles (6mm-25mm total) – If you have Speedplay pedals, you can swap longer pedal spindles in differing lenths (+3.175mm, +6.35mm, +12.7mm) to get the exact width specified by your fitter.
- Shimano Ultegra Wide Pedals (8mm total) – If you prefer Shimano, you can opt for their +4mm Ultegra pedals that provide almost an additional centimeter of width if needed.
After addressing pedal stance, the cyclist ends up with correct cleat placement, knees that track straighter and no accumulated knee pain after steep climbs or long days in the saddle. Wedges are too often used to align displaced knees at the detriment of long-term pain-free cycling.
For the Pedal Manufacturers
Statistics will vary for each geographical area, but, for South Orange County, (San Clemente, Dana Point, San Juan Capistrano, Mission Viejo), the pedals that I see during bike fits are typically 80% Shimano Dura-Ace/Ultegra, 15% Speedplay and 5% LOOK. Twenty miles south in Encinitas (North San Diego County), I am sure that Speedplay is the dominant pedal since Encinitas is the ‘Triathlon capital’ of SoCal and where Speedplay headquarters is located. Based on bike fitting metrics I’ve collected, I recommend that manufacturers modify their pedal axle widths to meet cyclists needs for such a critical dimension of bike fit.
On the other hand, bottom brackets and cranks on mountain bikes are designed and built with a larger Q-factor than road bikes, placing most MTB riders with the correct pedal stance. You will know if your pedal stance (usually determined more by Q-factor) is too wide. If so, your knees will start diving inward at the top of the pedal stroke and you might experience pain as well.
Have any burning questions you want answered? Send Rick your questions HERE
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