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Bike Fitting - Knee over the Pedal Axle ?

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Bike Fitting - Knee over the Pedal Axle ?

Old 08-30-04, 11:10 AM
  #1  
Corsaire
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I always thougth that the " Knee over the Pedal Axle " was one of the crucial points to have a good bike fit, but this guy on the link below advises that is just non sense, according to him what REALLY MATTERS is your weigth distribution fore and aft position which is determined by the fore-aft position of the saddle relative to the cranks.

I'm confused...what gives ??!

http://www.peterwhitecycles.com/fitting.htm

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Old 08-30-04, 11:16 AM
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Originally Posted by Corsaire
I always thougth that the " Knee over the Pedal Axle " was one of the crucial points to have a good bike fit, but this guy on the link below advises that is just non sense, according to him what REALLY MATTERS is your weigth distribution fore and aft position which is determined by the fore-aft position of the saddle relative to the cranks.

I'm confused...what gives ??!

http://www.peterwhitecycles.com/fitting.htm

Corsaire
Keith Bontrager also says it's hooey. And it's not just about weight distribution,but the knee/pedal relationship that works best for you...It's a place to start. Don't live or die by any of the fit guidelines, coz they are just guidelines,that may not work for everyone.
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Old 08-30-04, 12:13 PM
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Originally Posted by Corsaire
I'm confused...what gives ??!
I saw Peter Whites article and Keith Bontrager's as well. I think one of them said itís merely coincidental that most peopleís knee ends up over the pedal axle. I like this part of Peter's artcle:

Try this test. Youíll need a friend to hold the bike up, or set it on a wind trainer. Sit on your bike with your hands on the handlebars and the crank arms horizontal. If you have a drop bar, hold the bar out on the brake hoods. Try taking your hands off the bar without moving your torso. If itís a strain to hold your torso in that same position, thatís an indication of the work your arms are doing to hold you up.
I think this is perfectly logical and Iíve used the test recently after buying a new saddle and a tandem. Iíve been riding seriously for 15 years and I had no idea on how to position a saddle fore/aft other than knee over pedal axle.

-murray
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Old 08-30-04, 01:10 PM
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Corsaire
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Originally Posted by Murrays
I saw Peter Whites article and Keith Bontrager's as well. I think one of them said itís merely coincidental that most peopleís knee ends up over the pedal axle. I like this part of Peter's artcle:



I think this is perfectly logical and Iíve used the test recently after buying a new saddle and a tandem. Iíve been riding seriously for 15 years and I had no idea on how to position a saddle fore/aft other than knee over pedal axle.

-murray
....however here's where my confusion lies: it ALSO makes sense to get the "knee over the axle pedal" correctly set for LEVERAGE, more power on the downstroke so to speak, so what set up should be first : fore & aft comfort position or knew over the pedal....hmmmmm!

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Old 08-30-04, 02:39 PM
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Originally Posted by Corsaire
....however here's where my confusion lies: it ALSO makes sense to get the "knee over the axle pedal" correctly set for LEVERAGE, more power on the downstroke so to speak, so what set up should be first : fore & aft comfort position or knew over the pedal....hmmmmm!

Corsaire
If this is true, why are all of the human powered vehicle records held by recumbents (except for the records that specifically exclude them)?? Well, except maybe climbing records

To answer your question, I would go for comfort unless you have an accurate method to measure your power output in various positions. As the article states, moving forward provides more power, but puts more pressure on your hands, hence the tendency to ride "on the rivet". Moving forward allows your body to lean into the pedals a bit more. I wouldnít want to hold that position for 50 miles, though.

-murray
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Old 08-30-04, 06:07 PM
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Here's KB's article on The Myth of KOPS >>> http://www.sheldonbrown.com/kops.html

Although many people disagree with Keith, I believe what he has to say about the whole issue and find his arguements compelling. What he does state though, is that short of getting properly fitted by a bike physiologist and fit expert, KOPS will at least get you somewhat in the ballpark, but then again so will any other coincidence. KOPS should not be mistaken for an 'essential fit element', simply because it has no basis in fact. ( as does many other blindly accepted fit 'facts', but that's a whole other thread )

Weight distribution is also very important. Your CG ( centre of gravity ) in relationship to the wheels is a big part of what dictates how your bike handles ( Which is ironic considering almost no bike company factors that into their stock geometry ), and those that do usually have some weird idea that every size bike must attempt to fall within a 3" or whatever window.

I agree, fit is confusing, but my general observations thusfar is this.

1) People generally sit too far forward. There are very few people on the planet that require a 73 or 74 degree seat angle with a non-offset post. There's a reason most people sit too far forward - riders generally have poor flexibility, and the majority of posts nowadays are non-offset design.

2) What's happeneing here is also riders compensating for poor CG/weight distribution. If the rider had a more rearward position and slightly longer stays, this would fix that problem.

3) A more forward position seems to shiftswork from muscles in the back of the leg to he front of the leg. This is probably more powerful for short distances, but the muscles in the rear of the legs ( glutes etc ) are larger and more adept to endurance efforts, and a rearward position also appears to work all the muscles of the legs more evenly. This is annecdotal evidence, but appears from my POV to be true.

Fit is a very complex issue and really, only sports physiologists that specialise in cycling really have a handle on it - the rest of us just amass info from the web and the experiences of ourselves and others. The best thing you can do is keep an open mind, realise that everyone is different and that bodies do adapt.
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Old 08-30-04, 06:17 PM
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Biomechanically, Peter White is correct - there is no way physiologically that knee-over-pedal can provide the same fore/aft positioning result for all body types. I remember in the dim, dark past when I bought my first "serious" road bike, can distinctly remember the sales guy goin', "...how does it feel?". Truth be told, I was probably lucky to be facing the right way - how the heck did I know how it was supposed to feel! There's the rub - feel is relative, and you have to have miles under your belt before you know what feels right and what doesn't, position where you generate the most/best power and where you don't. I think that the knee over pedal, like all sweeping statements, covers the big part of the bell curve, but leaves out a bunch of folks at the upper/lower end. I think the "formula" gives those with less experience or knowledge, be they salespeople or customers, a way to be right more often than not.
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Old 08-30-04, 06:21 PM
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Originally Posted by Steelrider
Truth be told, I was probably lucky to be facing the right way...
LL.
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Old 08-30-04, 07:44 PM
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For time trials and triathlons, you want a forward seating position to generate the max power for a relatively short period of time. The bike will have a large seat tube angle which effectively rotates the saddle forward about the crank spindle. That'll put your knees forward of the pedal spindle. You'll notice that the rider sits forward on the saddle nose which puts the knee even farther forward of the pedal spindle. The knee is still properly aligned with the pedal spindle, it just has nothing to do with gravity( or does it?).

For endurance and comfort, you want to balance your weight over the bottom bracket spindle. That puts my knee 2.5 to 3 cm behind the pedal spindle. It probably varies a lot as I move back and forth on the saddle a few inches to change my position every once in a while. Supposedly, having the knee behind the P spindle that much interferes with maintaining a high cadence. I spin easily to 110, cruise at 95 to 100, so it's not a problem too me.

The setback of the seat post effectively reduces the seat tube angle and provides a more rearward sitting position which often puts the knee behind the pedal spindle.

When my wife started riding 40+ miles on her bike, which is built on a touring frame, she started to complain that she felt too far forward. So I measured her knee position and found she was about 1" forward of the pedal spindle. That was a big surprise since her seat post has an inch set back. Something was wrong since touring frames generally have around 72 deg. seat tube angle. I measured her bike's angle and came up with 74. I checked the Trek site and sure enough, Trek 520's have aggressive angles and in her frame size it's 74. That's close to time trial territory I believe. My old touring frame, which I no longer ride, is 72.5 deg.

My fist thought was she needed a new bike, so I called a touring frame builder to see what gives and found out that smaller frames, which women often use because of short upper bodies, have to have steep seat tube angles to get adequate toe clearance with the front wheel, much less the fender. The only option was to get more seat post set back. There's only one, the Titec Hell Bent. It's advertised at 1.5 ", but I measure 2". Now she's happy. We left the stem length alone as she seems to be OK with the weight distribution. If she needs to go back more, the only option left is a men's saddle since they have longer rails which might allow another half inch or so. Sitting position is a compromise.

I bet there's at least a few short upper bodied women and generally just shorter people out there who are uncomfortable on their bikes because they are sitting too far forward.

Lennard Zinn, Zinn's Cycling Primer (p 5) makes two interesting points. (1) The center of rotation of the knee must be over the center of rotation of the pedals. That argues for the knee over spindle theory. Zinn says he's observed this from 3-D digitized videos of riders, (2) "the saddle is a tool for support only; it does not actually determine where the rider sits. Pruitt says, "the pelvis will find the place it needs to be to get the knee over the pedals""

There's plenty of theories, opinions and folklore out there for everybody. The best thing to do is to experiment and go for comfort. What's comfortable will likely change as the mileage and experience increases.

I take most of the stuff in most books with a big grain of salt. They tend to be race bike oriented. I find Peter White's stuff is more relevant to me as are books on randonneur cycling like the Complete Book of Long-Distance Cycling. They are not weight centric and focus on endurance and comfort.

Al
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Old 08-30-04, 08:02 PM
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If you think about it, like KB says, gravity has absolutely no effect on a riders ability to pedal efficiently. Look at a recumbent - how does KOPS apply here? If it had any real world relevance, or basis is physiology, recumbents wouldn't work. The reality is, your knee is always over the pedal spindle, just not in relation to gravity. Silly humans.
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Old 08-31-04, 05:03 AM
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I feel you ( or we ) can take all of the info and use it to get the best fit possible. In the book The Lance Armstrong performance program, by Lance and Chris Carmichale. In chapter 4 Riding Positions, page 41 Fore/aft saddle position, you can find the ( or and ) answer to your question. These guys do know what they are talking about, at least I feel they do. Good luck on getting fitted.
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Old 08-31-04, 05:38 AM
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I move fore and aft on my seat during a ride. I don't worry about milimeter differences in seat position since I doubt my butt lands on the same spot on the saddle each time.

I start at KOPS and adjust to feel, but I have been riding awhile so I know what feels right for me.
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Old 08-31-04, 05:53 AM
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when fitting a bike, i use kops as a starting point. i find that people with longer shins tend to prefer to have the saddle backed off a bike, and people with longer thighs prefer to have it a bit forward. but, in a fit, you really have to rely on the feedback of the person you're fitting. comfort is not something that you can reduce to numbers and rules. you have to ask how the rider feels. it's a bit time consuming, but i find that it works.
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Old 08-31-04, 06:54 AM
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Originally Posted by Freestyle
I feel you ( or we ) can take all of the info and use it to get the best fit possible. In the book The Lance Armstrong performance program, by Lance and Chris Carmichale. In chapter 4 Riding Positions, page 41 Fore/aft saddle position, you can find the ( or and ) answer to your question. These guys do know what they are talking about, at least I feel they do. Good luck on getting fitted.
They really do know what they are talking about because they have experimented with cycle-mounted power measureing equipment under controlled conditions. That and a heart rate monitor can tailor the "optimum" sitting position to the individual rider. Lance armstrong has a unique build and some back problems so his position is different than the "norm". For example, he sits more erect than most racers. However, all this stuff is not relevent to many of us because we have different cycling objectives than Lance.

If I was into racing, I'd spend the $1000.00 for a power meter and experiment myself.

Al
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Old 08-31-04, 07:09 AM
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Got to be flexable and adjust what feels and works,not whats written down as thats only a guide and not in stone.
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