You probably wouldn't see any lower power.

I output almost the exact same power on a 200 or a 175.

Don't over think it. the 155 or the 160 will both be fine. Pick the one that gives the best position without impacting your run.

My fitter actually recommends a170 but I'm still dealing with some hip impingement at that length

Thru all research and testing done and there's not a single watt lost going with a smaller crankset!

From a 172.5 to a 155 could be too agressive of a chage, first go 165mm or 160mm... anything less than that will put in a 110-115 cadence lol

I went from 172.5 to 165 and it was the best change I've made! Cadence increased about 7-10% as well as my HR! Went from a low 80's cadence to mid 90's and i like it like that a lot more!

Also your BB will be a limiting point if it's anything other than a bb30! Couple of people selling Rotor PM 160mm crankset check them out.

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Speed kills unless you have speed skills!!!

Don't you lose some torque climbing up a hill due to the shorter lever arms? I believe you would need to use the next cog up on the cassette when going from a 172.5 down to a 165 to compensate.

This is correct, you gearing will need adjusting however, not even a fraction of watt is lost! Instead when climbing is done with shorter cranks; you'd want to either climb outta the saddle or simply shift to a easier gear and cadence your way up the hill.

If you're a grinder as i used to be then there will be a period of adjustment needed as getting used to the higher cadence will initially tire you out and elevate you HR 10-15 bpm higher, this is something you will easily adapt to anywhere between 5-10 rides & the longer and higher cadence you do/maintain the rides; the faster you'll adapt and eventually you'll go back to the previous gears you used before changing crankarms length.

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Speed kills unless you have speed skills!!!

i just switched from 172.5 to 160mm on my tri bike. I'm much more comfortable now and my knee tracks less on my impinged hip. I retested my ftp and it didn't change. I went from a 53t chainring to a 50t chainring and my average cadence is exactly the same although I do catch myself spinning a little higher sometimes. My LBS thought I was nuts wanting to go so low but I love it. Heck, I'd probably order 155's if I could go back. Going to the smaller chainring I am a little worried about spinning out on descents, but living in South Florida it'll probably be a while before I get to test that out.