Flexible frame and bike fit (shoe wedges)

Equipment
1

Was reading some of the stuff on how a flexible frame shouldn’t make a bike slower:
https://www.renehersecycles.com/myth-4-stiffer-frames-are-faster/

But I don’t think that’s a full view of the issues as they only used the bike a short time and didn’t adjust to it and deal with long term issues

Was thinking wouldn’t a less stiff frame in terms of side to side movement in the bottom bracket make for a different fit? In that when doing a fit wedges are sometimes needed to angle the foot to get the knee to track better. If a frame flexes then the pedal won’t be parallel to the ground but be at an angle in the same way a wedge would act. If someone gets fitted on a stiff bike (guru fit bike) and then rides a bike that flexes the effective angle of the foot could be different leading to a fit issue.

Am I missing something cause I never seen anyone take up this view?

2

Surely a frame with more flex would allow the pedal to stay MORE parallel to the ground? Assuming by “flex” that we’re talking about deflection around the bottom bracket area

If you imagine how the bike rocks from side to side slightly whilst pedalling, a super stiff frame with no flex would surely keep the pedals more perpendicular to the bike and less parallel to the ground?

I agree that fitting on a static bike isnt the perfect solution for mimicking outside riding but I can’t think of an obvious better solution.

3

For steady-state endurance biking, not a sprint or standing or anything like that. I’m not saying the bike will be ridged but that the rocking is less than the flex on a flexy frame