Often when out riding on the road or on the local bike path, someone will fly past me, tucked down on their aero bars. Invariably they will not speak.
It seems aero bars are only purchased by anti-social people, either that or after fitting these bars to a bike it gives one an extreme sense of superiority over lesser cyclists who don’t use them. But this is a whole different story.
The other thing I will often notice as this rider gradually pulls away to eventually disappear in the distance; his knees are splaying outwards as he pedals.
I find this kind of ridiculous, as any aerodynamic advantage gained from having the upper body in a low tucked position, is lost by the rider’s legs splayed outwards, therefore increasing the frontal area and catching large amounts of air.
The other point is to pedal efficiently legs need to pump straight up and down like two pistons. If the knees are splaying outwards the rider is not achieving maximum power.
The problem may be that the rider’s knees are striking his elbows at the top of the pedal stoke, and he is bringing his knees outward to clear. But more often it is a sign the rider is sitting too low, or too far back, or a combination of the two.
Often a cyclist will ride knees out even with regular bars; the problem is the same. There is a limit to how far your hip joint will rotate in its cup in the pelvis. To demonstrate this stand with your back to a wall and raise your knee forward and upward as far as it will go.
This is the limit of the hip joint’s rotation and the only way you can make the knee go higher is to move the thigh outward. You can also demonstrate this if you try to squat with your knees together, you will not get your butt very close to the ground; but squat with your knees apart and you can get much lower.
This is exactly what is happening when pedaling a bike. If your saddle height and/or the fore and aft saddle position is set where your hip joint reaches its limit at the top of the pedal stroke, your knees cannot help but splay outwards.
Also if you lower your back to achieve a more aero position, often you will rotate the pelvis forward, thus limiting the movement of your hip joint further. This is especially true if your spine is not flexible enough to get the back low without rotating the pelvis.
Don’t place too much importance on “Knee Over Pedal” (KOP) position, it is not that important. Look on it as a guide (A place to start.) rather than an absolute rule. The same with saddle height, this should be as high as is practical.
When the pedal is at the top of its stroke, (With your back in its lowest position.) you should be able to lift your foot a centimeter or so above the pedal, before your hip joint reaches its limit. In other words your hip joint should operate at slightly less than its limit at the top of each pedal stroke.
If your saddle is too high, your hips will be rocking as you pedal, and you will feel that you are stretching at the bottom of each pedal stroke. It is easy to feel if your saddle is too high, less easy to feel if it is too low.
This is why the person with the aero bars who passes me on the bike path does not know his saddle is too low; it feels fine to him. Whereas I can see immediately that his position is wrong.
Saddle height is not a constant thing; as you lose weight and gain fitness your saddle height can be reassessed and probably can go a tad higher. Always move in small increments and see if it is an improvement. (Feels better.)
Rather than follow exact formulas when setting up your position; think of what you are trying to achieve and adjust the bike to reach that end. If your back needs to be low for aerodynamic reasons, then realize that this will affect your pedaling action.
To achieve one at the expense of the other is defeating the object.