I think I need pedals that allow my feet to pivot (“float”). It seems like they want to move on my current fixed-position pedals. However, I have heard that float can cause knee problems. Is that true? And what is “stack height”? Should I get a professional pedal set-up evaluation? -- Jeff E.
It's hard to know which pedals might work best for you without seeing you in action. That's what any biomechanical evaluator would want to do, too. A good one should be able to put riders in their best riding position from head to toe (literally).
In general, pedals with lots of float work fine for some riders and not well at all for others.
The tendency of the foot to pivot has to be countered by the tendons and ligaments near the back of the knee. They work to stabilize the foot and make the “pedaling on ice” feeling go away. In some riders on some pedals, this results in overuse problems.
That's not to say that pedals with more than 9 degrees of float (the maximum that most models allow) aren't good choices for riders who need the movement and don't develop soreness. But there's no need to start with extra float unless you're advised to do so by an expert.
Stack height is the distance between the bottom of the foot and the pedal axle. An ideal pedal would put them at the same level. That's impractical, but pedal and shoe designers try to come as close as possible.
The objective is to reduce “rocking torque” -- the tendency of the foot to roll forward as it comes through the top of the stroke and starts down.
Picture a tricycle with big wooden blocks on the pedals so a little kid can reach them. They make the trike harder to ride because the pedals want to roll over. Feet don’t push straight down but forward and down as the pedal goes from 12 to 4 o’clock.
In theory, a few millimeters less stack height gives you more power because your legs don't need to resist the tendency to roll the pedal over during the power phase of each stroke.
Coach Fred Matheny has decades of experience as a competitive racer and cycling coach. He is the author of 13 RBR eBooks and eArticles.
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