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Awright, who here believes in KOPS and why? I can't(28 posts)
|Awright, who here believes in KOPS and why? I can't||bill|
Jul 13, 2002 8:21 AM
|imagine how a cm difference in that fairly arbitrary norm can matter. And, if it's so important, how come recumbents work?
C-40 down below stated flatly that the proper KOPS relationship is essential for maximum torque. Why?
|I'm a believer.....||DINOSAUR|
Jul 13, 2002 8:43 AM
|It effects which leg muscles you use when you are pedaling.
1 cm forward pushes your weight forward and greatly increases the work of the lower leg muscles and half front of the foot, but hurts endurance, and perhaps your knees, as when I tried this position my knees started bothering me.
2 cm back puts the demands on the backs of your legs, some of the strongest muscles in your body. Provides more effecient downstrokes and when pulling back.
Neutral position with knee directly above pedal axle spreads pedaling force over greater number of muscle groups, lets knee work in strongest range of motion, best balance of pedaling action.
Another setting I found to be important is centering your cleats over your pedal spindle. Which I overlooked until I started to have a bout of pain with my feet and this is one of the things I did to make it go away.
Some people beleive in KOPS and others don't. But if you don't use this method to dial in your saddle what else is there? I did check my seat posts position relative to the center on the bottom brackett and it's dead center, guess this would work also if you do most of your riding centered on your saddle.
Maybe you should try experimenting and see what works best for you.
|I am because I spin and it works for me.n.m.||koala|
Jul 13, 2002 9:34 AM
|works for me||DaveG|
Jul 13, 2002 9:47 AM
|I am very confortable with a position just slightly behind KOPS. I can't defend the physiology of it but its seems to work for most people|
|because it works...||C-40|
Jul 13, 2002 1:14 PM
|Perhaps you've never been close enough to the "sweet spot" where a small amount of saddle fore or aft makes a noticeable change in torque or cadence. This optimum position is not likely to place the knee directly over the pedal spindle. I've never had good performance from this position myself. I prefer to locate the knee behind the pedal spindle 1-2cm.
Maximum POWER is what is important, not torque. Power = torque x cadence. You have to balance the two factors to optimize power output, without overstressing the leg muscles or the lungs. Adjusting the saddle position helps to achieve that balance.
I could care less if other people believe it or not. I suspect that's one of the reasons I see so many cyclists riding so slow with incredibly low cadence. No on ever told them that the saddle adjustment isn't used to change the reach to the bars.
Analyzing a recumbent would be interesting. Having never ridden one, I don't know how much emphasis is placed on the knee to pedal relationship in the frame design. It should be possible to apply the same principal to a recumbent. All you have to do is rotate the analysis the proper number of degrees. It should be entirely possible to establish the same KOP on a recumbent as a conventional road bike, you just can't use gravity (plumb bob) to help make the measurement. There would still be an angle between the upper and lower leg that would be equivalent to the 3 o'clock position. Perhaps that's why some recumbents don't work worth a damn. The designer failed to place the rider is the proper postion relative the crank.
|wait wait wait. think about what you're saying. if you can't||bill|
Jul 13, 2002 2:12 PM
|use a plumb bob to find the "sweet spot" on a recumbent, then what possible relationship does the saddle fore-aft, and the position of your knee over the pedal spindle relative to a plumb bob, have to do with your ability to produce power?
I'll say this -- I believe strongly that a very slight difference in saddle height can make a huge difference in my pedaling. I also believe that what people experience as the "sweet spot" in fore-aft positioning has more to do with leg extension than it does the position of your knee relative to the pedal spindle, because if you move the saddle back, at the same seatpost extension and saddle height, which most people don't change when they're playing with fore-aft position, you're lengthening your leg extension.
C-40, by the way, I singled you out because you seem to believe this very strongly. It ain't personal, my friend. It's strictly business. I'm just trying to get to some understanding of why this is considered so important, because I don't get it. All that would seem to matter by moving your saddle position a little fore or aft (assuming that you have adjusted the seatpost accordingly to account for the leg extension difference caused by the geometry of the seat tube) is that you would use a very slight, and I do mean slight, different range of flexion of your knee. The difference of a cm or two at the end of your lower leg would seem to be so slight (I can't do the math; I'm just picturing it, and you have a 20 in lever or whatever moving a cm -- it ain't much at the fulcrum of the knee), that I can't imagine it's making a difference.
|here's the relationship...||C-40|
Jul 13, 2002 3:31 PM
|A line, perpendicular to the crankarm, and through the pedal spindle, intersects the center of the knee joint. This only occurs at one point in each revolution of the crank. It has nothing to do with gravity, but the plumb bob just makes it easy to measure, with the crank in a horizontal position. You do understand that a plumb line is perpendicular to a horizontal line??
The reason you can't use a plumb bob on a recumbent should be obvious. The point is that you can still determine if a line perpendicular to the crankarm intersects the center of the knee joint at some point, but a very different method would have to be used to perform the measurement, with the cranks mounted in a variety of odd locations, as they are on recumbents.
I think you are way off the mark regarding leg extension. The leg does not apply any significant torque to the pedals in near the bottom of the stroke. The area of importance is around the 3 o'clock position.
Rasing the saddle 1cm moves it back by .29cm (with a 73 degree STA). This does need to be considered when moving the saddle.
When I get more time, I derive the formula for "leg extension". Gotta go now.
|with all due respect, haven't you gone some distance to||bill|
Jul 13, 2002 6:02 PM
|proving my point? If moving your saddle up 1 cm changes the fore aft by .29 cm, wouldn't changing the fore-aft by .29 cm change the effective saddle height by 1 cm? In other words, a far more significant (in absolute terms, anyway) difference? Do I have that right?
You are certainly correct that the point where the plumb bob is over the pedal spindle is where a line between the tibial notch or whatever it is and the pedal spindle forms a right angle to the horizon. But, why is that significant? It's not even as if your lower leg is now perpindicular to the horizon, which might make some sense to me because it would mean that gravity is now helping the direct force of your leg along the axis of your leg (I didn't say that I'd be convinced it mattered, I just said that it would have some relation to what else I understand is going on). But, you have at best an arbitrary relationship between the pedal spindle, which everyone agrees should go under the ball of your foot, and your knee. Take a guy with the same length upper leg as another guy with a bigger foot, and the relationship is off by more than that one or two cm.
I didn't come up with this by myself. I read an article by Keith Bontrager posted on Sheldon Brown's site. He's not convinced it means a damn, other than at best a dimension that is a by-product of a balanced fit but is in itself irrelevant.
If you think I'm way off on the significance of leg extension, think about this. Again, my math is completely inadequate, but you know how those car jacks work? The ones that you lift the car by rotating a crank that pulls together the symmetrical lever system? As you scissor together the sides of the two half-diamond levers, at their fulcrum, the sides move closer together than the ends of the levers push the car up. You leverage the distance that the crank pulls the fulcrums together to get the power to raise up the car.
The reverse is true when you pedal. The little bit of difference in saddle height has an outsized effect on the way that your knee (the fulcrum) moves.
I explained this badly; I lack the nomenclature and the math. But do you know what I mean?
|I'm more in line with C40 on this one.||Leisure|
Jul 14, 2002 1:05 AM
|What you're really looking for is getting in the biomechanical position that maximizes power output within the dimensional constraints imposed by other priorities on the bike, i.e.- weight distribution, aerodynamics, height of CG, etc. KOPS arrises secondarily as an easily measured rule of thumb that happens to be 95% acurate for 95% of riders on 95% of regular road frames. Assuming all other forces of fitment are right, KOPS will *tend* to work on a standard road bike. The classic rationale that KOPS works because of the angle your knee assumes relative to the ground is inaccurate. The complete biomechanical position is the key, and in theory can be replicated at any angle relative to the ground, which is why recumbents *can* be just as efficient and powerful as uprights.|
|didn't prove your point at all...||C-40|
Jul 14, 2002 4:51 AM
|I stated that you are correct in your assertion that saddle movement up or down, should be accompanied by fore or aft movement of the proper amount to maintain the same KOP position.
The saddle is NOT moved fore or aft maintain the same leg extension. If you did that, you would have to move the saddle fore or aft 3.5 times more than the amount that the saddle was raised or lowered! There's not that much adjustment available! That's why you raise of lower the saddle - to CHANGE the maximum leg extension.
Reducing the leg extension tends to speed up cadence because the hip flexes fewer degreeS per revolution of the pedal. Increasing it has the opposite effect.
You also are negelecting the flexibility of the ankle. Riders who place the saddle significantly higher must bend the ankle more at the bottom of the stroke (toes down) to prevent over-extension of the knee joint.
|You are mistaking my point. I'm not saying that you change the||bill|
Jul 15, 2002 6:04 AM
|fore-aft in order to set the proper leg extension; I'm saying that people who change the fore-aft to find the right fore-aft position end up changing the leg extension more than they think, and that leg extension is really the critical dimension in power generation. |
What's the first thing you do when you fit a bike? Set the seatpost height. What's the second thing? Hang the ol' plumb bob. How often does anyone then go back and compensate? And then what are you fooling around with after that, because it's easier to do? The fore-aft.
Jul 13, 2002 6:09 PM
|The important thing is to position the body where you can make the most power. Easier said than done unless one has a power output measuring hub or similar.
For us poor folks which can't afford such a device, I think the best thing to do is find a position which allows you to spin round circles with the cranks. If you can do this, there is a pretty good chance your position is about right.
|The biomechanical theory behind KOPS||MXL02|
Jul 13, 2002 6:37 PM
|Your initial query assumes that KOPS is an arbitrary norm. Actually the concept is derived from biomechanical forces related to knee extension. KOPS simply puts the pedal spindle directly over the midpoint of the femoral head, thus directing the maximal force/vector of the quads/knee extendors directly onto the pedal spindle. Does this actually translate into improved power, especially during the entire pedal stroke including knee flexion? It would be hard to prove this for each individual without a dynamometer.
The bottom line, like most measurements for cycling, is that KOPS is a starting point, and unless you are racing, it is probably not crucial if one is off a cm or so. Several cms though might cause decreased efficiency and increased fatigue over long rides...60-100 miles.
|You say that the pedal spindle directly under the femoral head||bill|
Jul 14, 2002 4:13 AM
|directs the maximal force/vector, etc., etc., but you're saying this about an instant in time, once every revolution (or twice, I guess), with the force being applied through this other lever, your lower leg, that is oriented completely unrelated to KOPS. This makes no sense to me, because there still is this angle between the upper and lower leg in this instant that would seem to be completely arbitrary, depending more on shoe size than saddle fore-aft position. Then the pedal turns, and you're off through the entire rotation, with the changing orientations. How could that instant matter so much? I understand that the KOPS position would help define exactly how the knee moves through the rest of the revolution, but it would seem to define the relationship just a tiny, tiny bit through a broad range of movement. Makes no sense to me.
Why do you say that the position directs the forces maximally?
|re: Awright, who here believes in KOPS and why? I can't||bic|
Jul 13, 2002 8:39 PM
|OK, if I move my fat ass on the saddle does it effect KOPS?|
|bic, your fat ass raises an excellent point, and I thank it. If||bill|
Jul 14, 2002 4:00 AM
|KOPS is so important, why are people getting out of the saddle when they really need to turn it on? Out of the saddle throws that whole relationship way, way, way off.
I'm thinking that KOPS is one of those things like Eskimos and their 22 words for snow. It seems as if it could be true, it's widely believed, it's even widely quoted in print. But it just ain't true.
Like I said, I didn't come up with this. Y'all should read Keith Bontrager's article, "The Myth of KOPS."
|Think about it this way.||Len J|
Jul 14, 2002 5:26 AM
|At KOPS, my knee is over Pedal spindle at 3 o'clock.
If I st up behind KOPS, isn't my knee over the Pedal spindle at some point before 3 o'clock?
Likewise if I setup ahead of KOPS isn't my knee in the exact same position over the Pedal spindle except at 4 or 5 o'clock? (All of this assuming that the saddle height is adjusted properly for the rotation around the BB).
To me it's pure geometry. KOPS is a myth, but a myth that (on a diamond frame) gets people in a good starting position. I here people talk about torque, but again, KOPS may get maximum torque coming over the top of the pedal stroke, whereas the geometry would say that ahead of KOPS would move the maximum torque from (Maybe) 12 o'cloclk to 1 O'clock. It's still a circle,
Think of a recumbant, the riders ass has rotated behind horizatal KOPS, the seat heigh has been adjested (I.E. the distance from the ball of the foot to the hip has been maintained, & (Absent gravity) KOPS has been moved to somewhere between 11 o'clock & 2 o' clock depending on how high thee BB is relative to his hips.
I think Nessism hit it on the head when he said that KOPS happens to work for 95% on 95% of the frames, to get CG in the proper place on the bike.
This sounds like a ramble when I reread it. The simple fact is that if you take the center of the BB as a fixed point, start with a rider at KOPS, and rotate hime around that fixed point, you maintan that same knee to spindle position just at different points on the clock. (Oviously, further back & the rider of a diamond frame needs to be less upright & forward, more upright.)
CG is the most important measure, KOPS is a substitute.
|What I did....||DINOSAUR|
Jul 14, 2002 7:39 AM
|I had my new Master X-Light professionally fitted for me by the owner of my LBS. When I got home and installed my pedals I had my wife check my KOPS with a 1 cm set-back as that is the position I'm in with my old Klein. Since then I have put on 1100 miles on the new bike and and just yesterday I found "it". "It" pertaining to the sweet spot where everything feels like it's dialed in. I've moved the saddle up-down, fore-aft numerous times. Then I purchased a new pair of cycling shoes that threw everthing out of whack.
I'm not a particular technical type guy, I set up my bike to guides and then go from there. I really couldn't tell you what my KOPS is right now, I think it's in a neutral setting. When I'm centered on my saddle and my hands are on the hoods I feel like I'm spinning little circles and my knees don't bother me, and the main part is that it just feels right. But is does change when I stand or scoot forward or back in my saddle depending on what I am doing.
Another point not covered is the geometry of your bike and the angle of your ST, it would make a difference (I would think) from bike to bike. Both my bikes are set up differently as they are different animals; one has a forward riding position and a long TT and the other has a centered riding position with a short TT.
But if you don't use KOPS to position your saddle on your seat post for a starting point how do you determine where to place your saddle? You have to start somewhere....then if you purcase a new bike with the same geometry it saves a lot of fooling around as you know where to position the saddle.
Wonder if old guys like Fausto Coppi ever heard of KOPS?
|What I did....||eddie m|
Jul 14, 2002 8:47 AM
|KOPS has no biomechanical basis at all. Anyone who everused a legpress machine in a gym can that tell that the force of extension to raise the weight is a vector directed on a line through the hip joint parallel to the path of motion. Move your foot forward to make your lower leg parallel the path (KOPS in bicycle terms) and you become much weaker. On a bike, the force vector is approximately parallel to the seat tube, and the max torque occurs when the cranks ar perpenticular to the seat tube, not when they are horizontal as KOPS assumes. Keith bontrqager's method is more analytically correct, and he accommodates an optimum standing position, but it's too complicated for the real world of sales pressure.
KOPS probably works for 99% of riders of normal body dimensions, but for guys with unusual dimensions, it puts them in a custom frame they may not need if a more mechanically correct analysis were done. I have a friend who went for a $5000 custom bike based on KOPS, and it hasn't made any difference in his riding as far as anyone can tell.
Jul 14, 2002 9:47 AM
|KOPS is reference point and not a religion.. its just a tool..a way to standardize conceptualizing a "neutral/optimal' position by relating the body to fixed points on a frame... that's all ...
in general i ride just a few mm's behind KOPS if not exactly there.. it works for me and allows a starting point for bike set-up..
its just a way in.. but it isnt the way...
this arguing seems to be pointless as it is taking place in the realm of the theoretical.. reality never works like theory.. theory is just a reference point or a way to communicate what happens in reality..
KOPS is only relevant if ti is used in a relevant way....
I think its great because it is repeatable and intellectually accessible...
like life..bike fitting is not black and white.. because there is no standard human body.... this seems to me to be an arguement about theory versus reality and speaks more to black and white thinking and the inflexibility of the understanding of how to apply a tool to a certain task...
this isnt religion... it is about communicating and replicating fit.... which for a long time was an intuitive art...
KOPS is a way to standardize a phenomena of fitting a person to a bike... its a tool that you have to decide how to use for your body..
get it, got it, good.
|I got it.....||DINOSAUR|
Jul 14, 2002 4:09 PM
|What you said makes sense....I got it by carrying a couple of hex wrenches and stopping numerous times in the middle of some rides and making a few changes. Your body is a marvelous machine if you just listen to it.....cycling is not rocket science...it's what works for you...but I think KOPS give you a starting place and you need to adjust from there...|
Jul 14, 2002 9:35 AM
|Within reason. Though I started setting up my bike via KOPS simply based on what I was "told," it has been enough years of tweaking my set up that I've noticed a few things.
In my observation, KOPS seems to give me a balance of muscle groups used throughout the pedal stroke. That is, well I've put my saddle too far forward, especially in rides with lots of climbing (I'm in Colorado), I've gotten two things: knee pain and slight hamstring cramping (or at least excess hamstring fatigue).
When I've had the saddle too far back, I've gotten burned out quads without feeling like I'm adequately engaging my hamstring.
If Keith Bontrager has a different perspective, bully for him. He can go debate Ben Serotta, whose Sizecycle fittings rely on pure KOPS. I'm not a physiologist or a frame builder, so I'll rely on my personal experience supplemented by the majority wisdom on the issue.
Of course, I'm sure you can now post an ad hominem rant (as you did to others above) telling my how wrong I am. But I doubt you'll be changing my mind; as I doubt I'll be changing yours.
|I do.||eddie m|
Jul 14, 2002 10:03 AM
|I think KOPS is way more accepted in the retail sales community than in the coaching community. The Serotta size cycle is the perfect example. If starting the process with an irrelevent arbitrary constraint on knee position that can only be satisfied by a custom frame (when an equally acceptable position could be found that did not result with the knee-over-the-pedal), who's the winner?|
|no ad hominem rants over here. I just would point out that your||bill|
Jul 15, 2002 6:19 AM
|experience is absolutely consistent with leg extension issues. Seat forward, too little leg extension, using the hamstrings a bt much. Seat back, too much extension, all quads. |
I'm not saying that KOPS is very obviously all wrong. Because of the way bikes are designed, with wheelbases and seattube angles and top tube lengths and stem lengths for fit and stability such as they are, KOPS obviously is approximately correct. What I AM saying is that it does not bear scrutiny and does not deserve its sacred status. Within a couple of cm is bound to be close enough, and it's an accident of some other things that are more important.
|I think it's a good guideline, that's all. nm||DougSloan|
Jul 15, 2002 6:21 AM
|No one has answered this question...||DINOSAUR|
Jul 15, 2002 8:02 AM
|If you don't believe in KOPS what method do you use to place your saddle on your seat post? What method do you use? I'm curious. Lot's of arguments about KOPS but no alternative method has been outlined. Let's hear it. I'm here to learn....|
|I'll answer the question||eddie m|
Jul 15, 2002 9:31 AM
|The obvious answer is to start with correct leg extension regardless of knee position. From there determine handlebar position for proper reach and height. Check that you have the adequate range of motion of your femurs, and that you can stand and pedal comfortably (if that is important to you.) If that leaves you in comfortable and aerodynamic position, and results in controllable bike handling, you're done. If not, change the fore and aft position of the saddle and start again.
There are no arbitrary reference points this way, and you could come up with different solutions for different riders. For example, triathletes and time-trialists will want to ride with their saddle forward to allow them to get their shoulders low (for aerodynamics) and still have adequate range of motion in their legs. (That's exactly what triathletes do.) Road and crit riders will want their saddles back and their back to be a bit more upright, whether for bike handling or comfort or to have a better position when standing. KOPS doesn't accomodate any of those factors, and it doesn't accomodate the small number of riders with odd body proportions.
|I'll answer the question||DINOSAUR|
Jul 15, 2002 1:58 PM
|That sound about right. I just put one thousand miles on my new Master X-Light and finally got it dialed in. My solution was tinkering here and there. For some reason my feet have started to bother me. I customized my shoes with spenco 3/4 arch supports and I repositioned my Look cleats and everthing felt great, then today I raised my saddle a couple of mm's and my feet started to bother me again. I think my tolerance for a correct setting is that close. Of course when you an old guy in his 60's little problems become big problems after a couple of hours in the saddle...
For info~ I got fitted by the owner of my LBS and he refers to all bicycle fitting guides as a bunch of "mumbo jumbo". My main concern was the TT measurement as I have a short torso and have always had problems with TT and end up swapping out to a shorter stem. He took some measurements, all upper body, I know what my inseam is (34.50)and the ST height can be adjusted. He built my bike using his measurements and listened to me about my as to what I did not like about my old bike (a Klein). Everything dialed in..I have messed with the saddle height a couple of times, the biggest problem was getting the angle of the Deda Magic Bars right to dial in with the Campy Ergo brake hoods.
an old roadie told me once back in the late 80's to listen to my body when making adjustments on my bike, and that's how I do it. I start out with a neutral KOPS and adjust from there. Now I think I'm about 1cm back....but I'd have to check it to know for sure...
Thanks for your input...