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According to this article, a seat tube angle between 65 and 110° has little effect on max power output. At most, it varied 1%. https://www.me.utexas.edu/~neptune/Papers/jab26%284%29.pdf

Adjusting the setback would affect the effective STA. The reason for a more forward seat position seems to be an aerodynamic position.

If it works, it can allow wrong sized bikes to fit. If the bike is too large, the reach would be too long so to decrease it, the seat is moved forward. If the bike is two sizes too large, one might flip the seat post to move the seat even further forward. The opposite is true for a bike that's too small.

Is it possible it's rarely done because it affects aesthetics, preferred postures, safety reasons, or weight distribution?

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    The short answer is that maximum power output is only a tiny aspect of bike fit. I'll have a more fleshed out answer for you this evening.
    – Carbon side up
    Commented Apr 15, 2019 at 7:46
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    By shifting the saddle like this on a 'wrong' sized bike, you are likely to put yourself in a bad position in relation to the bottom bracket and leave yourself at risk of knee injury
    – Andy P
    Commented Apr 15, 2019 at 9:05
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    @AndyP bad position in relation to the bottom bracket and leave yourself at risk of knee injury If an "incorrect" knee position with respect to the bottom bracket leads to knee injury, how do recumbent riders ever walk again after riding? There are lots of ways to injure your knees on a bike. Moving your knees from 3" in front of a vertical line above the bottom bracket to 2" behind that vertical line is not one of them.
    – Andrew Henle
    Commented Apr 15, 2019 at 10:02
  • @AndrewHenle I said 'risk' not guarantee. I can only speak for myself, but I know I can tolerate different crank lengths and Q factors, but if my knees are forward of the KOPS point I get sore knees within a few days. I assume I don't have a unique anatomy, so others could also be injured in this way.
    – Andy P
    Commented Apr 15, 2019 at 12:47

1 Answer 1

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Bike fitting isn't just about maximising peak power output. In fact it's rarely even the priority. The study that you've linked only touches on absolute max power without looking at any other factors which may actually be more important for most cyclists. This study is only really relevant to track sprinters who have to do a max power effort, almost as soon as the race starts.

The most important thing for most riders is comfort. For recreational riders, this is because they enjoy riding more when comfortable. For racers, this is also important, because it becomes very difficult to race for hours on end if your bike fit is uncomfortable.

The study doesn't look into the effect of saddle position over the course of a longer effort. You might find that while the difference is only 1% in a max effort, it could be far more important when looking at the power that can be produced for hours on end.

Bear in mind that elite track sprinters will spend very little time on their bikes at all. They always set it up for their very short race efforts, because it doesn't matter to them how they feel on their bike after 20 km of riding, because they don't need to do that. Be wary of applying the findings of this study to cycling in general, because track sprint is a very specific discipline with very different requirements which don't apply to the rest of cycling.

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    Right. The conclusion of this research is liberating. Like crank length, changes in STA don't have much effect on max power so you modify it to optimize other goals (like, comfort, or aerodynamics) without worrying that it will restrict max power (if max power is important to you, and for most cycling it really isn't). So STA is a variable you can change, it's not a hard-and-fast constant that you have to use as given.
    – R. Chung
    Commented Apr 15, 2019 at 16:51
  • In the case of a track sprinter, yes. Anyone else should ignore this research. If they repeat this testing with threshold or sub-threshold efforts, then we can get an idea of how STA changes will affect power output. Just because absolute peak power isn't affected doesn't mean that that's true for all power zones.
    – Carbon side up
    Commented Apr 15, 2019 at 21:21

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