Don't think thats an issue. in my cycling days I went between 170's on the TT bike, 172.5s on the roadie, and 175's on the mountain bike with zero issues.

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My TT Bike is 172.5. My road bike is 175.

I don't even notice a difference. The geometry is different, anyway. The bikes are different weights.

I'm a firm MOP LC person (5:3X HIM and 12:5X IM), so I might not be your best test subject :)

I have 175's on my mountain bike and 172.5 on the road bike... the difference between those two lengths is barely perceptible.

As you increase crank length, your ideal fit moves the saddle down and forward. Then, in order to maintain the exact same overall position, your bar position would also need to move. At some point the stem length and the stack height become an issue. But, lower seat = lower centre of gravity, which generally improves handling. On the other hand, the longer cranks put your pedals closer to the road so then pedaling through corners can become a problem.

The thing that will probably limit the practical crank length you can use, is how high you can raise your leg (pedal in top dead centre position) without running into your torso, and while still making good power. The crank length and how it affects your pedal speed can be compensated with gearing.

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Less is more.

I'm 5' 11 1/2" with long legs and years ago as a cyclist when long cranks were in vogue I went to 175 and since starting triathlon and going now to 160 on my tri bike I went to 170 on my road. With your hip angle so much more open the issues aren't as great but I figured it would serve me better not getting too different. I prefer riding the 170 and feel more powerful including hills I can only guess because I have a more efficient pedalling action. The one place I think I notice the difference is racing where there are sudden accelerations you react faster with a longer crank/lever. I have no velotron data but it just feels better and my position is also slightly better on my road bike too.

I work fly in, fly out in the oil and gas industry for weeks at a time and have a cx bike at work. I put 165 on that and it feels shorter than I would prefer but there is only flat dirt tracks or trainer to ride and it all centres around my Ironman training.

Maybe try 165mm cranks on your time trial bike.

With the endless debate...you need to try it for yourself. I started out as a Pro on 172.5 ..went to 175..and noticed a significant advantage..never went back during Pro career.

I tried the short thing about 10 years ago. It didn't work for me. I went from 175 to below 170 on the TT bike. Performance deteriorated..went back to 175's...back to previous levels.

I'm 5'11 and have a 34" inseam ...average I suppose? I ride a big gear and push high wattage...just can't do it with a small crank.
But again...I'm not convinced either way as far as making a general statement. I would give it a shot and see.
All I know is that if I ride a crank below 170 and switch back to 175's...my performance jumps significantly higher.
It remains a mystery I think?

There’s no way you will notice a difference.

How do you know you cannot push a high wattage with a "small crank"? Do you have data to show you tried and it did not work?

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I just got my 1st ride in in my road bike, now equipped with a 165 crank vs the prior 172.5. It felt great. I'm 5'3". I had been feeling like my knees came up too high and today's ride was more comfortable. Also exciting - the new power meter (Quark) was in constant contact w/ my Garmin and therefore a much less frustrating experience that most recent rides w/ the prior one (Stages). Yay.

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Back in the day, I rode 175s on my roadie and 177.5s on my TT. At the time, we believed that longer cranks provided better leverage. For reference, I'm 6 ft and have a 33 inch inseam. When DuraAce 7800 came out, the 175s weren't available because the pros were getting all of them, so I rode my new Litespeed with 172.5s.

As I got older, my knees became a little less flexible. In 2013, I bought a large Giant TCR Advanced. It came with 175s. They caused my knee to bend more acutely coming over the top and it was painful.

So, if you have knee flexibility issues, you will be able to tell the difference with longer cranks.

I think the general consensus from ad nauseam discussions about this is that there are a range of crank lengths that work. Anecdotally, I am 5'10" with a 30" inseam meaning my legs are a lot shorter than yours and I am switching with my bike build from a 172.5 to a 170. You being at a 172.5 with a significantly longer inseam than me makes a lot of sense. Just like I'll bet my stem is longer than yours as my torso is longer than yours given our inseams.

The one thing I will say is you won't find the answer to this question on here. Many others, yes, but not this one.

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2018 Races: IM Santa Rosa, Vineman Monte Rio, Lake Tahoe 70.3