Bike Fitting Advice Needed: How Critical is Having the Kneecap Directly Above the Pedal Axle?

by andyspaceman   January 29, 2014  

I have long legs and a short torso for my height - 5'11 with a 33/34" inside leg (depending on how you measure it and which brand of jeans you believe).

So for a bike to fit me well, it needs a frame that is proportionally tall when compared with it's cockpit length. Or a big stack for a given reach in bike fitting parlance. Some people would call these sportive bikes.

However, one subtlety is that much of my leg length is in my femurs (the top half). I had a professional bike fit a couple of years ago which positioned my saddle and bars nicely in relation to one another, though the bike fitter was also adamant that despite my long shanks, it was really important to still get my kneecap directly above the front pedal axle with the cranks in a horizontal position - for optimum power transfer.

I get the theory, but the result of that is:
- the saddle is positioned way back on it's rails, on a layback seatpost
- a short (90mm) stem to stop me having to stretch too far
- my centre of gravity is positioned towards the rear of the bike
- meaning I compensate by moving forwards whenever I need the front tyre to bite hard in a tight or fast turn
- meaning I can't remain seated as much as I would like on very steep climbs, and when I do get out of the saddle I occasionally bang my knees on the bar

I also feel like I'm over-using my glutes - I get a lot of muscle tightness in my hamstrings and backside that takes a lot of stretching to get rid of, whereas my quads never really feel too fatigued.

I know that it's theoretically better to use this muscle group (over the quads) primarily, because it's a much bigger/stronger group that can store more energy. But I am tempted to slide the saddle forward slightly to redress the Centre of Gravity issues, and try recruiting my quads a little more and glutes a little less.

Any experienced bike fitters out there? Do you reckon I should give it a go, or is that just a good way to decrease my power? I have a 100mm stem sat in the garage, so could easily shift the whole cockpit forward slightly in equal measure.

I run 175mm cranks, and mostly do 40-60 mile recreational rides once or twice per week, though usually tend to push myself quite hard.

All sensible advice will be greatly appreciated, especially by my aching bum cheeks!

11 user comments

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hello, i would agree with the front of the knee cap directly down over the centre of the pedal axle, i have done it myself with a spirit level on last couple bikes. i used to have my saddle too far back which gave me more power on hill etc but when i moved saddle forward, i noticed i could spin faster up climbs instead and felt like it freed out my hips,felt restricted or something before. I got faster on the flat as well. Are you sure your saddle isnt too low.also i am the same height, pants leg as yourself.i use a 172.5 crank, had a 175crank and a 170crank on diff bikes. could spin mad on 170 but power on hills was less. 175 felt too big for me in range of motion. Steve Hogg does a great video on the fundamentals of bike positioning, look it up.i played around with cleat position more,heights of seatpost, saddle position etc till i got to where i am now. also on a side note stretching is great too for cycling, gets the tension out of the muscles and recover faster in my opinion.

posted by 27humpy [4 posts]
30th January 2014 - 0:13

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sorry forgot ask what size bike you have and what geometry has it

posted by 27humpy [4 posts]
30th January 2014 - 0:16

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Keith Bontrager and the myth of KOPS.. http://sheldonbrown.com/kops.html

I'd shove your saddle and bars forward by 10mm and see how it works out.

posted by Malaconotus [34 posts]
30th January 2014 - 2:22

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Fascinating reading. Thanks for the link.

"If the seat tube angle is too shallow [saddle too far back], rider [center of gravity] will be well behind the position where it is comfortable and efficient for out-of-the-saddle riding. If he jumps out of the saddle for a sprint, he may hit his knees on the bars. In the climbing position, the rider may have to lean back uncomfortably far, putting extra stress on the arms and shoulders. In most cases, the rider can put just as much power in the pedals, but only at the expense of upper body comfort ... In my experiences so far, I've found that most riders are suitably positioned with a seat angle that falls between 72 and 74 1/2 degrees. What is important is that I have not noticed any specific correlation between seat angle and my customers' femur bone length. I am reasonably certain that none exists."

Sounds like moving your saddle forward may solve your problems. Your LBS will likely have an angle level to help determine how far forward you need to go to get a seat angle between 72-74.5 degrees if needed. FWIW, my seat angle is 74 on my Pinarello and was worlds more comfortable than the 75.5 degrees I had on my old Kestrel Talon.

Melancholy is incompatible with bicycling. ~James E. Starrs

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posted by movingtarget [100 posts]
30th January 2014 - 3:52

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27humpy - it's a 56cm Genesis Equilibrium, with 'a few' modifications.

I got into road cycling about 5 or 6 years ago, but had well over a decade of MTB behind me at that point, so 175mm cranks were a no-brainer. I've always run them offroad, so they've always been comfortable on-road too. That said, I'm on my second folding commuter bike with 170's, and have done a couple of seasons on the track on 170s too. So I'm not too picky there.

My bike fitter was trained by Steve Hogg, which is why I'm a bit hesitant to go against the advice. Had a look at his video - he makes a convincing case.

But...one person I'll always listen to is Keith Bontrager. And I get his physics and reasoning - that was a really good read. I need to go and measure the seat angle I have set up currently. The Equilibrium has quite a steep seat tube on the frame (74deg on the 56cm), but with the layback post and seat positioned where it is, I reckon I must be a little way south of 72 degrees.

I think I'll get the allen keys out this weekend...thanks for the tips.

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posted by andyspaceman [207 posts]
30th January 2014 - 23:09

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I've always seen the KOPS as a starting point, but certainly not the holy grail it is often lauded as.

I always have a snigger when I see a club riders bikes with the saddle slammed back on the rails, a 130mm stem slammed as low as possible, all in order to attain the 'pro' look.

Than you look at pro's bikes and yeah, most of them run 130mm stems slammed down, but the saddle is actually quite far forward... hence the low and long stem (well partly anyway).

Balance on the bike is more important (IMO) than KOPS. Can you ride in the saddle with the hands off the bars and maintain your normal riding position? If you fall forward, chances are your saddle is too far forward and needs to come back, if not, then play with moving it forward.

Also, if you have long femurs, you may want to experiment with moving your cleats back on the shoes as another option.

posted by Jimmy Ray Will [105 posts]
31st January 2014 - 13:46

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No-handed stability is good, so it sounds like I have some room to play with.

The bike fit I had started with cleat & foot position, and I've been pretty happy with that aspect since, but it's an interesting thought. I'll try tweaking one thing at a time:
1. seat position
2. longer stem
3. cleats

It sounds like KOPS is a nice thing to have, but not at the expense of COG/balance. So it's going to be sacrificed...

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posted by andyspaceman [207 posts]
31st January 2014 - 14:21

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Not very critical, look at recumbents.

posted by felixcat [173 posts]
31st January 2014 - 17:02

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I've read the bontrager article before and found it interesting. While he explodes the myth of kops, he doesn't really give an alternative which is the real shame.

I use a great bike fit guy but he agrees that after an adjustment period, if it's not comfortable or not working, it's not right, no mater what the science says. Get a set of scales under each wheel in turn and see what the weight split is between front and rear. Try for 60/40 or 55/45 rear/front as a starting point.

posted by onzadog [3 posts]
1st February 2014 - 9:45

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sounds like your saddle is too far back and stem too short, when i went with front of knee over centre of axle etc i ended up saddle positioned about on seatpost. i will give my measurements to give u an idea what works for me anyway. i have a 2007 trek madone 5.9sl, a 56cm. its 56cm exactly from the centre of handlebar to tip of seat. 70cm centre of handlebar to centre of saddle rail in seatpost clamp. 70cm from centre of bottom bracket to centre of saddlerail etc. i dont know your measurements exactly but we are both 5ft 11 so it will give u an idem anyway. jamming a book under my crotch against the wall to ground gives a leg length of 33 inches. and from the fork crown on fork to under the stem is 180mm. best of look anyway

posted by 27humpy [4 posts]
5th February 2014 - 22:07

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sorry forgot to add i use a 100mm stem

posted by 27humpy [4 posts]
5th February 2014 - 22:11

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