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Thread: KOPS Measuring

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    KOPS Measuring

    Hey Everyone,

    So I know KOPS isn't the end all be all and just a starting point, but I seem to be 1-2cm ahead of KOPS even after a bike fit. I get this by dropping the plumb bob over my knee and seeing where it lands in relation to the end of the crank arm. I wanted to ask the correct way of measuring...

    Is it from end of the knee cap (longest part sticking out) to the end of the crank arm, or the tibial tuberosity to the pedal spindle? I've read both methods and trying to determine which is the right one.

    And yes, I know my bike fit is most important, but really just seeing how close I am to KOPS out of curiosity.

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    Quote Originally Posted by ejewels View Post
    Hey Everyone,

    So I know KOPS isn't the end all be all and just a starting point, but I seem to be 1-2cm ahead of KOPS even after a bike fit. I get this by dropping the plumb bob over my knee and seeing where it lands in relation to the end of the crank arm. I wanted to ask the correct way of measuring...

    Is it from end of the knee cap (longest part sticking out) to the end of the crank arm, or the tibial tuberosity to the pedal spindle? I've read both methods and trying to determine which is the right one.

    And yes, I know my bike fit is most important, but really just seeing how close I am to KOPS out of curiosity.
    tibial tuberosity is what was used in any bike fit I have had where they look at this.
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    Either method is acceptable. Dropping the plumb bob OVER the top of the knee and having it just graze the END of the crank arm is easier to see, which makes it more convenient, not necessarily more correct or accurate. Dr. Andy Pruitt recommends this method for its simplicity as well.

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    Thanks guys. I take it being a little in front or back is a preference thing? Due to different anatomy like long femurs I find it harder to achieve KOPS

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    Quote Originally Posted by ejewels View Post
    Thanks guys. I take it being a little in front or back is a preference thing? Due to different anatomy like long femurs I find it harder to achieve KOPS
    I'm beginning to appreciate more, Lennard Zinn's theory which is basically, everybody gets a 73 degree seat angle and you ADJUST CRANK LENGTH accordingly.

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    Quote Originally Posted by ejewels View Post
    Thanks guys. I take it being a little in front or back is a preference thing? Due to different anatomy like long femurs I find it harder to achieve KOPS
    I'm like 2 cms forward. The only way I can ride with enough drop to feel like I'm not sitting up like a sailboat. Otherwise my knees hit my chest.

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    Quote Originally Posted by Peter P. View Post
    I'm beginning to appreciate more, Lennard Zinn's theory which is basically, everybody gets a 73 degree seat angle and you ADJUST CRANK LENGTH accordingly.
    Where does he recommend saddle fore-aft?
    With or without setback and what amount?

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    Quote Originally Posted by ejewels View Post
    but I seem to be 1-2cm ahead of KOPS even after a bike fit.
    When you do this, try dropping or raising your heel and see what happens. What I'm getting at is, it's difficult to get it accurate. Not only that, it turned out to be useless way of setting up for me and I have long femurs too.

    Try this video instead.


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    Quote Originally Posted by Chader09 View Post
    Where does he recommend saddle fore-aft?
    With or without setback and what amount?
    He advocates typical KOPS position, so whether you need a setback seatpost or not and the amount is still determined with a plumb line.

    His theory about seat angle is, taller riders are prone to back problems when the back-to-thigh angle gets too acute, which is what happens when you slacken it to accommodate longer femurs. (73 degrees is assumed to be used in conjunction with setback seatposts). Note that Zinn offers extra long crank arms on his web site.

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    Thanks guys. Seems it's not a big deal if not perfect KOPS. Also seems some think it's bogus too.

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    It is bogus for people with long femurs.

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    Quick question I forgot. I assume your foot also has to be level horizontally with the crank arm when measuring? Assuming you don't drop your heels or point down when you pedal.

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    Quote Originally Posted by ejewels View Post
    Quick question I forgot. I assume your foot also has to be level horizontally with the crank arm when measuring? Assuming you don't drop your heels or point down when you pedal.
    Technically, this is done by a second person who observes your foot position at the 3 o'clock position while pedaling, then tries to replicate your foot position while setting up KOPS for you. If you don't have the luxury of an assistant then yes; a horizontal pedal is fine.

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    But it is so inaccurate that it's basically a fool's errand.

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    Quote Originally Posted by bvber View Post
    But it is so inaccurate that it's basically a fool's errand.
    what is so inaccurate if you know you pedal fairly horizontally? KOPS in itself is debatable right?

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    Quote Originally Posted by ejewels View Post
    what is so inaccurate if you know you pedal fairly horizontally? KOPS in itself is debatable right?
    The method to get it accurately is very difficult. As someone mentioned already, someone else needs to watch the movement and determine what the rider's natural foot angle is. Slight dropping or raising the heel can throw the knee location off thus making the measurement inaccurate.

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    BTW, if you are trying to further improve your fit, KOPS isn't something to go back to especially after you've already gotten the fit done (post #1).

    Are you having pain somewhere or not getting the power output (being passed by some ol-man on beach cruiser)?

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    Just curious that's all. Seems to get a ballpark and knowing you pedal fairly horizontally, it's accurate enough. Especially if you're not trying to get perfect KOPS

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    Until someone comes out with a better method than KOPS, I'll use it. Right now I don't know of any.

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    Quote Originally Posted by mfdemicco View Post
    Until someone comes out with a better method than KOPS, I'll use it. Right now I don't know of any.
    A better method for...what exactly? Why do you use it again? What's it helping you do on the bike? Simply figure out a place to put your saddle with no consideration of reach or drop or hip angle or anything?

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    Quote Originally Posted by pedalbiker View Post
    A better method for...what exactly? Why do you use it again? What's it helping you do on the bike? Simply figure out a place to put your saddle with no consideration of reach or drop or hip angle or anything?
    I don't understand your questions. You know what KOPS is for.

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    Quote Originally Posted by mfdemicco View Post
    I don't understand your questions. You know what KOPS is for.
    My question contains the assertion that you don't know how to set yourself up on a bike and are just blindly putting your saddle in a position relative to your knee because that's how it's been done in the past.

    Kind of pointless. Might as well put in straight in the middle because it looks better. About the same merit.

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    Quote Originally Posted by pedalbiker View Post
    My question contains the assertion that you don't know how to set yourself up on a bike and are just blindly putting your saddle in a position relative to your knee because that's how it's been done in the past.

    Kind of pointless. Might as well put in straight in the middle because it looks better. About the same merit.
    So what is your method, smart ass?

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    Quote Originally Posted by mfdemicco View Post
    So what is your method, smart ass?
    Well, that's cute.

    My method? I orient my saddle to fit my performance needs, which is pretty much what bike fitting is all about.

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    Quote Originally Posted by pedalbiker View Post
    Well, that's cute. Do you feel better regressing to insults?

    My method? I orient my saddle to fit my performance needs, which is pretty much what bike fitting is all about.
    Well, that's a pretty descriptive and scientific method. Bravo!

    I recommend that most folks should use KOPS with one of the established seat height formulas (which BTW do have a scientific basis) as a starting point, then tweak from there, unless you can afford one of those expensive bike fits that use something like RETUL (which I did and it didn't move my position by much at all), rather than wing it. That should work pretty well for most people of fairly normal proportions on a bike that fits.

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