|KOPS -- Dino asked what people who don't believe in KOPS||bill|
Jul 15, 2002 9:52 AM
|believe -- this is what I think. |
I think that locating your tibial notch and dropping a plumb line to your pedal spindle and carefully measuring where the line falls in relation to the BB gives a false scientific rigor to something that has little to do with your tibial notch or your pedal spindle. I can't see any reason why KOPS has much of anything to do with power transfer, and, while I think that it could be a rather imprecise shorthand reference point for locating a saddle on the post, having SOMETHING to do with center of gravity as much as by accident as anything else, it certainly doesn't deserve the attention it gets as a rule.
I'll say this to the believers. I think that bike design, with the wheelbases that have become the standard, with the stem lengths that seem to accomodate a human being in the cockpit and that provide a ride that is alert enough but not too, along with the head tube angles that are being devised and rakes, chain stay lengths, seat tube angles, all of it, provide a platform for which KOPS Is not going to be a mistake. Slap a saddle on any bike that otherwise fits, drop a plumb line, and you're going to be within a few cm of KOPS. That's the way we make double diamond bikes.
BUT, I can't think of any earthly reason what the relationship of your knee to the pedal spindle has to your true center of gravity. Your knee in relation to the spindle is going to depend on your femur length, your lower leg length, and your shoe size, none of which has much of anything to do with your center of gravity on a bike. Then you have a lot of body above your waist, where people differ tremendously. You also have differences in the way you extend over the top tube. These things above your waist are far more significant to your center of gravity than your knee location. Add to that your natural movement around the bike as you climb, sprint, time trial, etc., and I think that KOPS is just not that terribly significant. The same guy on different bikes set up a little differently is likely to have a different center of gravity.
What I think is far more important is balancing your body on the contact points so that you aren't sitting too much or hanging too much on your arms, factoring in the upward forces from your pedaling style. Add to this the feel of the bike with a 90 cm stem versus a 130 cm stem and the degree of arc in the turn and the suspension factor. Which are all terribly subjective and imprecise (or difficicult to quantify, anyway).
So, what's the substitute to KOPS? Nothing truly satisfactory, certainly nothing as easy to measure, but that still doesn't make KOPS right as dogma.
Hey, don't get me wrong. I use KOPS, too. What else are you going to do? I just wanted to see a healthy debate about it, so that hopefully we all could learn something about the way that our bodies work on these machines.
No ad hominem attacks from me, either. That one hurt a little.
Jul 15, 2002 10:03 AM
|Don't know if this was already posted; I have no view one way or the other: http://www.sheldonbrown.com/kops.html|
Jul 15, 2002 4:15 PM
|Gosh I think I'm getting dizzy&^%. Did I mention my fat ass moving on the saddle?|
|forget about CG||ET|
Jul 15, 2002 10:53 AM
|I view it as the logical place, on average for the world, that one's knees ought to be, for otherwise there will be awkwardness in some part of the cycling motion, unless that is offset by an "awkward" cycling motion (e.g. toes pointed up or down at 3 o'clock when heading down to 6 o'clock). So call it a neutral position about which there will be variance. Still, you can't pick a much better starting place.|
|Mr. Fit...||Len J|
Jul 15, 2002 11:01 AM
|please explain why I should "Forget about CG".
It seems to me that this is the most important determiner of bike handling and stability. All of the other "Rules of Fit" seem to be aimed at getting the CG in the proper place (albeit indirectly). Why then should we... forgetaboutit?
|and what does toe angle at 3 o'clock have to do with KOPS? What||bill|
Jul 15, 2002 1:52 PM
|does toe angle at 3 o'clock have to do with anything, for that matter, because, as your lower leg circles around, your hips and your knees and your ankle are moving in relation to each other as you direct, and your toe angle, except at the bottom of the stroke, can be anything you want it to be. The only angle that may be of concern is whether you can't reach the bottom of the stroke without pointing toes down or up, which is completely a function of leg extension, because then, I guess, you have deviated from the smooth transitin of muscles throughout the circle of the stroke and introduced another motion. I think.|
|Sorry, but you've got it backwards||Kerry|
Jul 15, 2002 5:22 PM
|KOPS came about after measuring a bunch of riders (professional racers) with good position on their bikes. Reasonably consistent positions on the bike gave rise to the search for some way to guide fore-aft position. Measurements showed that KOPS +1, -2cm was a range that covered nearly everyone. So KOPS is suggested as a starting point, and then you go from there. Nobody (who is knowledgeable) ever suggested that this was a rigorous theory - it's the result of measuring people who are well-positioned on the bike. What's so complicated about that?|
|what means this, "good position on their bikes"?||bill|
Jul 15, 2002 5:54 PM
|seriously, Kerry, are you aware of an actual study? Never heard of it; I'm interested. I'm willing to have my mind changed. I'd be curious to see whether anyone actually took the same dudes and put them out of KOPS and saw what happened.|
|link: not specifically KOPS, but good description of CG concerns||Mr Good|
Jul 15, 2002 6:25 PM
|that's a good article. by negative implication, he doesn't||bill|
Jul 16, 2002 7:26 AM
|think much of KOPS as dogma, either. As my friend said below, it's a "pinch" of this or that.|
Jul 16, 2002 2:01 AM
|I think you're getting closer. There's a big distinction between KOPS as a measuring tool and the theories that have been put behind it. KOPS as a measuring tool arises secondarily as a good fitment for most people most of the time. Many of the witchdoctor rationalizations for why it works however are wrong. The one I keep going over is the whole plumb bob thing. Just because a plumb bob is vertical, the front of your seat *tends* to be vertical to the BB, and your knees *tend* to be vertical to your pedals people think there must be some correlation. People just feel obligated to come up with pseudoscientific reasons to explain every little coincidence. The plumb bob thing is part of the measurement, it happens to be a convenient way of doing it, and people shouldn't read into it further as if there's some mystical property buried in it's cuteness. There's nothing to analyze, it's like a cooking recipe where you add a cup of this and a pinch of that. What the hell is a pinch? Overanalyzing spoils the broth.
At the heart of it all, you are trying to achieve the right biomechanical power and efficiency, placing your CG correctly on the frame, aerodynamics, and getting the correct handling/steering characteristics. It's too complicated a system to have to work everything out over and over from scratch. Instead, people simplify and look at trends, and KOPS (again, strictly as a measuring tool) seems to have arisen as a consequence of these trends.
|well said, mon frer. I think that you're exactly right. but,||bill|
Jul 16, 2002 6:48 AM
|what's up with that subject line? |
People also don't like their sacred cows gored.