I’ve been trying to get a better understanding of proper fit, specifically hip angle. I see on SlowTwitch that it is 90 (+10) degrees with the line going through the ankle and on the the Bikesport site it appears to be 90 degrees with the line going through the knee. Notwithstanding specific rider and bike factors, what is optimal?
I would like to know also. I tried bringing it up in one of the “critique my blah blah blah” posts but no one would have it.
90-100 degrees
Line from ankle to hip with the pedal at BDC and the line from the hip through the shoulder
BDC is more or less in line with the seat tube.
It would appear from this website that the femur should be about 90deg from the hip-shoulder line
http://www.bikesportmichigan.com/features/exisitingfit.shtml
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I was fitted by a F.I.S.T. certified fitter and the angle from hip/shoulder line is not 90 degrees to either my femur line or the line to my ankle. There may be reasons for this that I will explore that have to do with the particulars of my dimensions/ flexibility etc, and my bike.
However, as Bikesports is F.I.S.T. certified, is the apparent difference from ST on this point the result of a change in guidelines that is not reflected on ST or due to a different fit philosophy on this point at Bikesports.
There appears to be consensus on 90 degrees but not on what the 90 degrees is in relation to, i.e., femur line or ankle line.
"There appears to be consensus on 90 degrees "
This seems to be a triathlon thing. Look at the top TT’ers and they’re usually running a more acute hip angle. Their slacker seat angles and low in the front positions dictate this. But of course they don’t have to run afterwards.
My hip angle is well over 90 degrees. I think I do this because I have hamstring flexibility problems. The more open angle probably helps this problem.
… what is optimal?
Hard to say, since anything short of a vertical (walking, running) stance compromises muscular power.
“Optimal” is a classic engineering problem – trading off constraints and benefits. In my view, “optimal” means “fastest going down the road.” Not “highest power” or “most efficient” or anything like that. Fastest down the road. In triathlon, we add the further qualifier, “and still able to run.” (Although the ability to run well has more to do with pacing on the bike than position.)
So, what is optimal? It will be different for everybody, and the guidelines that Dan and other experienced folks give are a great place to start. If you are really interested in finding that genuine sweet spot of tradeoffs, you can start testing various position tweaks with a powermeter and early windless morning bike rides on your favorite loop.
There appears to be consensus on 90 degrees but not on what the 90 degrees is in relation to, i.e., femur line or ankle line.
I use 90 degrees from the pedal axle (at its most extended point), to the bony point on the side of the hip (whatever it’s called), and out to the end of the collarbone. I like having the 90-degree line run an inch or two under my collar bone, so that my body angle is greater than 90 degrees. Any less than that and my thighs come up too close to my torso.
I don’t know if it is optimal though. 
"My hip angle is well over 90 degrees. I think I do this because I have hamstring flexibility "
C’mon Art. Age has a bit to do with this. It’s the curse of the boomers.
And conservative views on life never made anybody appear younger. 
Interesting that the Bikesports pictures use the femur as the guide for the hip angle. FIST doesn’t use femur at all (below taken from the tribike fit article on the Slowtwitch main site) but Bikesports may have thought that the femur is easier to display pictorially, easier to understand, etc… Also note that Slowman is amenable to a hip angle of up to 100 degrees, which compares well to the Bikesport hip angle of 90 deg, since Slowman takes his hip angle measurement from the hipbone to the pedal axis vs the “femur” line that Bikesports uses.
Each of the three riders represented at right are in a position that is appropriate for triathlon racing. One immutable rule is that the range of motion in which your thigh musculature operates ought to be biomechancially sound. We might roughly refer to a “hip angle” that is formed by using the bony protrusion of your hip (greater trochanter) as the apex, and with that angle’s lines being: 1) one that run from the hip to the foot, and, 2) from the hip to the bony protrusion of the collarbone.
That hip-to-the-foot line is a little tough to nail down. Ought it to be from the hip to the bottom bracket? Or to the maleolus (bony protrusion of the ankle)? Or to the pedal axle? If so, where? At the bottom of the pedal stroke? With the crank in line with the seat angle (or relative seat angle)? If it’s the hip angle you’re measuring, why measure the angle in its most obtuse configuration? Why not at its most acute, when your foot is at the top of the pedal stroke?
All these are valid observations, but it doesn’t much matter. If the proper bike fit is in fact proper, it doesn’t matter where you measure, but each of these lines formed by the proximal point (hip) and the terminus at the line’s distal point (ankle, BB, pedal axle, whatever) is going to change depending on which distal point you choose. I personally favor the pedal axle at the bottom of the pedal stroke, and my definition of “bottom” (for the purposes of measuring this angle) is not at 6 o’clock, but at the point where the axle is in line with the seat angle.
The preferred angle is 90-95 degrees, and while I don’t like angles more acute than that, I don’t mind a more obtuse angle, up to a point. I can in some cases live with 100 degrees. I have a problem living with an angle greater than that. As long as this is your hip angle, however, it doesn’t matter to me whether you’re riding at 71 degrees or 81 degrees of seat angle. Realize, however, that as you rock yourself back in the saddle you’re rocking yourself up in front, that is, your back will not be as flat and you will probably be punching a larger hole in the wind as you propel yourself forward.