October 23, 2020

Stacking up problems

Stacking up problems
In this case study, bikefitter Matt explains how a simple alteration such as a change in pedals can lead to unexpected problems

Interesting little fitting session today with David, a long-standing customer and even longer-standing cyclist. After years of riding with Dura-Ace pedals he had made the switch to Speedplay Zeros, and started experiencing some minor knee niggles, which is obviously not ideal. Being a thoughtful kind of guy, he realised that the new cleats and pedals might have a different stack height to his existing ones, which if true would effectively be altering his saddle height.

And he was right to think this, because pedal/cleat stack height can vary quite significantly, with a lower stack effectively increasing saddle height because it sits the foot closer to the axis of the pedal spindle ("stack height", being the distance between the axis of the pedal spindle and the sole of the shoe).

Might not make much of a difference, you may think, but the difference in stack between, say, a Look Keo cleat and a Speedplay Zero could be as much as 8.6mm, depending on how the latter is mounted. Definitely significant in bikefitting terms.

To get an idea of how much stack height can vary, here are some examples of stack heights for common road pedals:

  • Shimano SPD-SL -13.7mm
  • Look Keo - 17.1mm
  • Speedplay Zero with 3 bolt adaptor - 11.5mm
  • Speedplay Zero with 4 bolt direct mount - 8.5mm
  • Time Xpresso/Xpro - 13.5mm

Unfortunately, David had over-cooked things a little by dropping his saddle around 10mm, when the stack difference between his Speedplay set-up and his old Dura-Ace pedals was actually only just over 2mm. This too-low saddle height was the cause of his knee issue, so referring back to his original measurements meant it was a simple matter to make the correct adjustment. Running our Retul motion caption system over him confirmed all was as it should be, and he left with confidence in his set-up restored.

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