I find myself coming back to this thread every time a post occurs on it. I do use a powermeter on my tt bike but really wanted to breakdown the force that a human body really creates. So I Google searched for a watts to horsepower calculator.http://www.rapidtables.com/convert/power/watt-to-hp.htm
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If my goal is 300 watts for a time trial I'm putting out about .402 of a horsepower. A 1600 watt sprint equals a little over 2 horsepower but this type of wattage cannot be maintained very long.
I then wanted to put this into perspective by looking at other things I have some knowledge of that create power. My motorcycle creates 102 hp and 110 fp of torque. My car is rated at 260 hp. I then look at the number of mounts that hold my motorcycle engine in place verses the power and it makes a bicycle crank look pretty beefy. Really the same goes for my car.
I still feel the stiffness has really no effect on speed and have not felt flex in crank since my early days of multisport where I could get my chainrings to rub on the derailleur cage when really pushing big gears. That could have been a combination of bottom bracket, crank arm, chainring and frame flex. Considering I was winning races overall I don't think it slowed me down.
I'm really just thinking aloud here but do feel free to throw rocks.
PS It does seem logical that the weakest link would flex first such as a tire since its a soft structure and visibly flexes just pushing hard on the bike.