Bike fit: is the knee over the pedals spidle recomedation arbitrary?

Discussion in 'Cycling Equipment' started by Rock Creek Rider, Feb 9, 2019.

  1. Rock Creek Rider

    Rock Creek Rider New Member

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    For many, many years, since before most of you were born, maybe even before I was born, bike books and experts have been recommending adjusting your bike so that, when the crank arms are horizontal, a plumb line dropped from your knee would pass through, or slightly behind the forward pedal spindle. It was a widely accepted truth. In the last 20 years I've heard a lot of people saying it is just bunk, based on no real logic or any data to support it.
    I think there is a lot of good logic behind some of these arguments, but this sage advice wasn't arrived at arbitrarily. If my memory serves me, it is based on a study done by the Italian Cycling Federation, or whatever it's called over there. They took measurements of a number of bike racer's on their bikes and found that the average put the knee over the pedal spindle.
    Is there a better method? First off, your seat and handlebars have a serious relationship. Moving the seat changes that relationship. You have to consider how moving the seat affects that relationship. It could be good or it could be bad. Moving the seat forward or back might be the right move, but if you don't also change the stem, or change the stem spacers, a good move may seem like a bad move. Moving the seat forward or back also affects effective seat height. Move the seat forward and you've effectively lowered the seat. Move the seat back and you've effectively raised the seat.
    I think this is where a power meter and bike stand type trainer come into play. I think with enough fiddling around, you can find the position that gives you the most power. You just need to keep in mind that moving the seat forward or back changes the relationship with the bars and affects effective saddle height.
    One last thing, and I've argued with a lot of cyclists about this, including one that most of you have heard of. If the distance between your saddle and your handlebars is ideal, then moving the seat backward can cause you to slide forward on the saddle. It may not change your relationship to the bottom bracket, you might just end up sitting on the nose of the saddle instead of the wide, comfortable part. For a lot of people experiencing seat pain, this is the cause.
     
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  2. dabac

    dabac Well-Known Member

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    Not arbitrary, but perhaps accidental.
    It isn’t that keeping the knee over the pedal spindle as such that’s important, it’s simply about there it ends up for most normal-proportioned people.
    It was so predictable as it ended up being used as a fit guideline, just like it’s possible to use saddle height wrt hip to get the saddle at about the right height as long as you stay with the same kind of bikes.

    KOPS as such doesn’t work that well during riding. Real-life riding involves a fair amount of movement on the bike, only occasionally passing through the KOPS spot.
     
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