|Disregarding the KOPS method||rayclark|
Jun 11, 2003 7:26 PM
|I've read a few articles that state, and have been told, that the KOPS method is really not a valid way of adjusting for/aft positioning of the saddle. While I'm not going to say that I disagree with what I've read or been told, I question what exactly is the best method in determining what the for/aft position should be.
Can someone explain exactly what this adjustment benefits? I've seen it stated the it should not be used to adjust reach. However, one thing I don't understand with that statement is that anytime you move the saddle you are also adjusting the reach. What guidelines do you use to determine if changing the saddle position would be correct or if going to a different length stem would be better.
Does changing the for/aft position have an effect on the knees? Does it only affect your pedaling? Is it used to get you more balanced? Does it play hand in hand with the stem for adjusting reach?
I ask these questions because I am in the process of making fit adjustment and I am a little confused as to what to change. Seat height adjustment is pretty straight forward (you want a good leg extension)but determining the for/aft position doesn't seem to be as easy. Any info, comments or insight would be welcome.
Jun 11, 2003 9:10 PM
|I set it to where my butt wants to be when I'm riding no hands--ie what feels natural and comfortable--it's a bit behind KOPS for me. This is the first adjustment I make on my bikes. Then I figure out where I want the bars to be.|
|If it feels good, it is good!||dzrider|
Jun 12, 2003 4:28 AM
|Much like the last poster, I ride behind KOPS, and I may not be as fast as I could be, but I ride without knee or back or shoulder problems. I ride on the stand with my hands behind my back and make adjustments til I find the magic spot where all is right with my legs and butt. This can take a while and doesn't always get done the first day.
Once the seat position is set, with my hands behind my back, I slowly lean forward until my cadence picks up involuntarily and it's hard to bend further forward. I reach forward and place the brake hoods to support my hands with my upper body at that angle and my arms lightly bent at the elbows.
I used to measure the triangle formed by the bars, seat and pedal at the bottom of the stroke and try to make all 3 bikes the same. I found this was less effective than the above method for getting each bike feeling as efficient and comfortable as possible. Either I'm a different man on a different bike, or numbers aren't what they're cracked up to be.
Jun 12, 2003 5:30 AM
|I firmly believe more comfort and personal efficiency can be obtained through progressive tweaking than by any given 'fit system'.|
Jun 12, 2003 12:23 PM
|I place the saddle where my butt things it should be. It's actually pretty close to KOPS though.
However, I tend to move around a lot while riding. I sit at the back of the saddle when I'm turning a lower cadence with more power, and slide to the middle when I spin.
|okay, my take on this is that when you slide back to get||bill|
Jun 12, 2003 12:36 PM
|more power versus slide forward for the cadence thing, you are varying your LEG EXTENSION. I do the same thing. And when I'm consciously upping my cadence, I tend to slide forward without trying to, because moving my legs faster is easier, for reasons still unclear to me but I'm buying it, with less extension. The difference in the physiological experience and the kinesiology is not related to the position over the bottom bracket, it's about leg extension.
That's my story and I'm sticking to it.
Jun 13, 2003 5:21 AM
|if youre sliding forward or back on your saddle, correct. also correct if you're sliding the saddle on the rails without adjusting the seatpost.
Whenever I slide the saddle I change the post accordingly; thereby keeping leg extension constant at all times.
|Recumbent bikes show that KOPS is nonsense||Continental|
Jun 12, 2003 4:48 AM
|People can generate as much power in the recumbent bike position as the KOPS position and the knee is way behind the pedal spindle.
If the saddle is behind the KOPS position then the pedalling stroke during leg extension is down and slightly forward which will push you slightly backwards to keep you from sliding off the saddle and to keep weight off your hands. I find this to be the most comfortable position.
Jun 12, 2003 4:52 AM
|There is nothing sacred about KOP, it's just a starting point, but there is a relation between KOP, torque and cadence.
Placing the saddle further back will generally enchance the ability to apply torque, but may sacrifice maximum cadence and vice-versa. Since power = torque x cadence, torque and cadence are equal players in the equation. If your saddle position causes you to apply too much torque, you'll easily go anaerobic and the legs will burn won't hold up for a long ride.
I recommend determining a reach from which the saddle can be adjusted .5cm fore or aft without discomfort. If adjustments are made that exceed the comfortable range, a shorter or longer stem should be installed to properly evaluate the saddle position without confusion from the effect of changing reach.
You can use the saddle fore/aft adjustment to experiment with reach, but you have to keep in mind that your pedaling action will change. You should restrict this experimentaion to determining the appropriate stem length for a comfortable reach. Changing reach is strictly for the purpose of maintaining knee to elbow clearance and/or controlling the angle between the arm and torso. My minimum reach dimension provides at least some small clearance between the knees and elbows when riding with my hands in the drops and the upper back horizontal. I can increase the reach at leasst 1cm from this minimum without discomfort. Additional reach is of no significant value, IMO. If you want a lower position, drop the bar height instead of increasing the reach.
Saddle height isn't that simple either. If the saddle is moved back 1cm, it should be moved down .3cm to maintain the same maximum leg extension. If the saddle is placed too high, maximum cadence and power may be reduced. I always make sure that I can drop my heel several cm below horizontal with my leg locked out at the bottom of the stroke. I rode for years with my saddle 1-2cm higher than necessary. A lower saddle position has significantly improved my cadence and the smoothness of my pedaling.
|How/why does moving the saddle back increase torque?||bill|
Jun 12, 2003 7:24 AM
|How/why does moving the saddle forward increase cadence? I don't mean to pick on you, C-40, but these are the sorts of things that get said in this debate without any real question. Maybe you have an answer. If you do, I've never heard it. I just want to know where this stuff comes from. I try to pay attention to these things because, well, because I'm a bike geek.
The lower the saddle, the higher the cadence (I agree with this, because I've experienced it, although I'm not entirely sure why it is). I half think, though, that people who say, saddle forward, higher cadence have found this to be so because moving the saddle forward lessens the leg extension.
I have sort of bought into the Bontrager balance thing, but it's a pretty mystical concept.
|Different muscle groups||Fez|
Jun 12, 2003 7:38 AM
|Different muscle groups are utilized. A rearward position would use the glutes a bit more. The glutes are a stronger muscle group, and since power = torque x cadence, the result would be more torque and power if you maintained the same cadence, or you would net the same power and torque if you reduced cadence. Depends on how you are approaching it.
I guess a physiological discussion could result as to whether a more fwd position actually promotes a higher cadence (due to leg angles and seated position rather than just the act of using the different muscle groups)
|You say that moving the saddle back makes you use the||bill|
Jun 12, 2003 12:00 PM
|glutes more. Does it? Aren't you just using a different range of knee flexion/extension, a very slight difference at that, to which you could get as used as much as any other?|
|You say that moving the saddle back makes you use the||Fez|
Jun 12, 2003 6:57 PM
|This topic gets varied answers. Lots of analysis here may be technically correct, but still, individual preference is a stronger factor on what works best.
My answer to your question is try it out yourself and see what happens.
My own experience is that when I was rearward of KOPS, I used my glutes more and I developed more power.
I started out riding this way. As I progressed, I was a rider who was rearward of KOPS and could maintain high cadence. Sounds great, right? Well, not exactly. I probably had way too much of my weight toward the rear. As a result, my bike handling and stability never felt that good.
I moved my saddle forward a bit, adjusted saddle height and stem length accordingly, kept the high cadence, worked on core strength and riding the drops more, and I feel much more stable on the bike now. I think redistributing my weight over the bike was a big factor.
|my personal experience...||C-40|
Jun 12, 2003 2:03 PM
|Not just repeating something I read somewhere. That's my interpretation after very carefully adjusting fore/aft positon, being sure to adjust saddle height to maintain the same maximum leg extension. The saddle must be moved .3cm for each 1cm of saddle height adjustment. In other words, moving the saddle forward or back by 1cm moves it down or up (respectively) by .3cm. A .3cm change in saddle height won't make any huge difference in your pedaling action.
Moving the saddle back hasn't reduced my cadence much, as best I can tell, but then I haven't shoved the saddle way forward in a long time. I can still hit 120 rpm if needed and maintain 100-110 for long periods. I just warn that moving the saddle back too much may reduce cadence. No two people are alike. That's why I avoid blanket statements.
I know your opinion that fore/aft position means nothing and saddle height is everything. I don't agree with that at all. Once the saddle is "low enough" there is a range where minor height changes are not noticeable. When changing brands of saddles there is absolutely no way to determine that your crotch is exactly the same distance from the crank by taking measurements. It has to be done by feel. I just set up a new bike with a totally different shaped saddle for more comfort. A tape measure got me in the ball park, but the fine tuning was done by feel.
The most important thing to avoid is a saddle that's much too high. It's not hard to gradually increase saddle height until you've raised it 2cm and achieved nothing but reduced cadence and power.
|awright, think about this for a moment. Doing geometry (which||bill|
Jun 12, 2003 2:50 PM
|I have not attempted since 7th grade) you have determined that, because of the STA, in order to maintain the same saddle height when you move fore/aft, you have to raise/lower the saddle .3 cm. I'm assuming you are correct. But, that only maintains the height relative to the floor. When you move the saddle forward, however, the operative dimension isn't the floor -- who cares about the floor -- but the pedal circle centered around the bottom bracket, and the BB is always forward of your hips. So, when you move the saddle forward, you may be maintaining the saddle height relative to the floor, but you are moving the saddle closer to the BB, and therefor lessening your leg extension.
That's my story and I'm sticking to it. Well, no, not really. I really do want to hear what you think.
|more thorough analysis....||C-40|
Jun 12, 2003 5:30 PM
|The .3cm dimension has nothing to do with measuring the height from the floor. Saddle height is generally measured from the center of the bottom bracket to the top of the saddle, along the centerline of the seat tube. If you move the saddle forward 1cm, the saddle should be moved up about .3cm to maintain approximately the same maximum extension of the leg. Otherwise, you are reducing your leg extension.
A really thorough analysis is more complicated. It helps to have computer drafting software, which allows the construction of a model bike frame, complete with a saddle and crankarm. The computer will allow you to move the saddle back and measure the maximum length from a fixed point on the saddle to the center of the pedal spindle. As the saddle is moved back, the angle and length of this "maximum length" line changes. The .3cm figure isn't perfect, but the error is very small. If you're thinking that it's a 1:1 ratio or close to it, you're mistaken.
Of course you don't need a computer to do this. It's high-school level trigonometry. A drafting table, paper and a compass will also tell the same story.
Jun 12, 2003 6:28 PM
|Decided to draw this up and use trig to figure out the answer. First, the "maximum leg extension" is always a straight line from the point of saddle contact, through the center of the bottom bracket to the center of the pedal spindle, regardless of where the point of saddle contact is.
To make this easy, I drew the simplest case. A line through the bottom bracket from the top of the saddle, at an angle of 73 degrees. I used my own typical saddle height of 72cm for this example. The maximum leg extension would merely be 72cm plus the crankarm length of 17cm for a total of 90cm. Now draw a right triangle with the 72cm saddle height line as the hypotenuse. The vertical side of the triangle (from the BB to the top of the saddle) is 72cm X sin73 = 68.85cm. The horizontal leg of the triangle is 72cm X cos73 = 21.05cm.
Now suppose the saddle is moved back by 1cm with no other changes. With the saddle contact point moved back 1cm, the horizontal leg of the triangle becomes 1cm longer to 22.05cm. The vertical leg of the triangle does not change in length, since the saddle movement is horizontal. To find the new "maximum leg extension", take the square root of the sum of the squares of the two known sides (68.85cm and 22.05cm)to get the length of the hypotenuse. The answer is 72.3cm. Add the length of the crankarm and you get 90.3cm, which is .3cm longer than the previous 90cm. The new angle of the "maximum leg extension" line is the inverse tangent of 68.85/22.05 = 72.24 degrees.
|First KOPS theory was center of mass, not reach.||micha|
Jun 12, 2003 6:10 AM
|When KOPS first came on the cycling scene, it was explained as a way to place the rider's center of mass directly over the bottom bracket to get the best possible bike handling.
Over the years, the idea of putting the rider's center of mass directly over the bottom bracket faded away. But fiddling with KOPS remained popular. Someone in the early 1970's just thought up a different reason for its existence.
|Another way to approach the problem...||eddie m|
Jun 12, 2003 7:03 AM
|I think handlebar position is more critical than saddle position. When you stand, you need to use your arms to hold your center of mass over or forward of the bottom bracket. That is obviously much more difficult if the bars are in the wrong place. Once the bars are optimally located, it should be easy to find the right spot for the saddle, if you ignore the KOPS thing. (This is similar to the Keith Bontrager approach.) Of course, determining the right spot for the bars requires more judgment and experience than is typically found at your LBS. I doubt that many elite coaches are concerned with KOPS.
KOPS is popular because it is easily determined and seems to be based on some scientific data. Mechanically, the position of the knee has no particular significance, but it is probably true that most riders are comfortable with KOPS. The problem is the religious application of it. What if you are a person with unusual body dimensions? Why would you believe that a rule determined by observing the positions of riders with average body dimensions would apply to you? I have a friend who bought a very expensive, very steep angle, custom bike, based on his KOPS position, but his riding didn't improve in any way that I've noticed.
Both recumbents and triathletes show that a wide range of fore and aft positions are effective.
As far as "KOPS as a starting point," why is that any better than "put the saddle at a comfortable height" as a starting point?
|re: Disregarding the KOPS method||MikeDee|
Jun 12, 2003 7:05 AM
|KOPS is important. First, it affects the weight distribution on the bike (which affects handling). Second, it changes the hip angle (the angle between the upper body and the thigh) which in turn affects power production. I can sure feel the difference in my legs when the seat is shoved way back vs. when it is moved all the way forward.|
|My take on this debate........||Len J|
Jun 12, 2003 7:48 AM
|is that KOPS is a great starting point but is not the critical thing that I pay attention to. Rather, for me it is balance on the bike.
I want my center of gravity such that there is balanced pressure on my hands & Butt. Think about when you bend over. Most people, the more they bend over, the further from center their Butt gets to counterbalance the forward lean of their body. The same is true on a bike. If your seat is way forward, all your weight is on your hands, the more you push the saddle back (within reason, the more your individual center of gravity is moved back and the less weight is carried on your hands (or the less stress on your abdominals/lower back needed to keep pressure off your back). Since everyones center of gravity is slightly different and everyones leg bone length is unique, KOP as a law doesn't work to provide good fit for everyone. As I said, it's a good starting point but not the end all & be all of bike fir.
As far as the torque vs cadence issue, I don't find it to be true in my case. As long as the center of BB to top of seat is constantno matter where my seat is, my cadence/torque stays the same. Obviously, if I change my seat from way forward to way back I will be using different muscle groups, but once the new position is "trained", there is no difference for me in torque or cadence.
|re: Disregarding the KOPS method||rayclark|
Jun 12, 2003 10:10 AM
|Thank you for all the input. Alot of good info. I think I'll try the hands behind the back method and see where that gets me. Seems like a good way to try. How much effect does the for/aft position affect the knees? I'm asking because lately my knees have been a little uncomfortable. Not really hurting but kind of like a very low grade ache. I'm just wondering where I should concentrate my adjustments to. Saddle for/aft? Saddle height? Reach?
|re: Disregarding the KOPS method||eddie m|
Jun 12, 2003 12:23 PM
|I think all the general statements like "a lower saddle helps you spin," and "moving back helps you make more power" are all based on the incorrect idea that saddle position alone determines these things. When the saddle is moved, that also chnges the its relationship to the handlebars. I think if you move the saddle and handlebars together, so that the riders position was unchanged but rotated slightly around the bottom bracket, then no change in spinning or power would result. I think that's why triathletes move their saddle so far forward. Their body position is probably pretty close to a traditional road rider's, but rotated forward to make the back low and flat for aerodynamic reasons. It will be interesting to see if triatheletes adopt a more traditional race position now that they are allowed to ride in packs, where aerodynamics is less important.
It's also interesting that both of the posters who determined their positions by riding with their hands behind their back set their saddles further back than the KOPS position. Maybe KOPS is just a compromise between setting the saddle back for comfort of efficiency and more forward for better aerodynamics.