So this is a bit of a tough question, as my body shape isn’t usual.
I have a short body, very long legs.
Around 6’1 and 37" legs.
But I have a longer LOWER leg.
I also have femoroacetabular impingement of the hip.
Because of the longer lower leg I have always struggled with an acute hip angle at the front.
This has really been helped by 155 cranks, but I am starting to feel they are too short for my long legs, and I keep being told they are an aero PENALTY because they expose more of long legs to the wind in the vertical plane.
The reason I feel they are too short is the great feeling on hills I get from 165s. But this is aero position is tough on my hip.
Is there anyone out there with long legs (relative to height) especially in the lower leg, and what cranks so you use?
If the 155’s help you train and race pain free I said f the aero penalty.
Interesting post and observation. I tend to think I have similar proportions, but not as tall. I’m about 5’9’‘- 5’10’’ with around a 33’’ inseam. From pics and how I feel, I think I do have longish lower legs + 10.5 US size feet (or skinny ankles/calves). I use 172.5 crank arms on my road bike which seems fine. On my tri bike, I switched to 165 this year. In training, it feels pretty good and I’m spinning more efficiently. Most of all, I feel like I can get a more even effort around the pedal stroke. My FTP is up slightly, but it might be more b/c of my consistent training. Wonder if 155 would work better for me! 
This thread has pics of me on the tri bike: http://forum.slowtwitch.com/forum/?post=6199000
I’ve prob shrunk to 5’ 11 1/2 now. 34" inseam. On my roadbike I have a 175 crank, but on the tri bike I use a 170. The short torso isn’t so noticeable on the road bike, but on the tri bike I had to put on a really short stem. From my 20’s to my 40’s, the tri bike also had 175s, but my position is more upright now then it was back then. I definitely like the 170 on the tri bike better than the 175.
Afaik, my upper/lower legs are proportional to each other.
It’s the long lower leg, combined with poor ankle mobility and a locked back which create all the problems!
Have you tried IMS therapy? Lots of needles later my back is much, much improved. Improved my swim without swimming. Same for bike!
No, can you give me some details?
I’m uk based btw
Just had a look at your thread, you definitely don’t have my proportions! Are you sure about that inseam?
If you have long arms too, you should just hang up the bike and swim instead. Sounds like the right proportions.
Curious what kind of bike are your riding and whats the size? I have a short torso and long legs, I am 6’1 my upper and lower leg lengths are the same. Interesting you are having hip issues, I had the same problem. First my seat was just too high, second my top tub was to long for my torso. I really had to shop for a bike that would fit my my dimensions (Trek). Look up the Cobb seat measurement tool, their numbers were almost exact for me. Good luck, BTW I don’t think small cranks are the solution. For your leg length 170? i would be comfortable with either 170 or 172.5, I am currently riding 172.5.
I am 6’ with long legs out of proportion for my height. I trialled many years ago on a tt bike before converting to triathlon 177.5 and was running 175 on my road bike. Since converting to race triathlon 5 years ago I started reading about how shorter cranks are more of an advantage. I went from 170 to 165 initially but still found I suffered some hip impingement especially at Kona on Hawi so I trialled 150 and found them too short before settling on 160 which feel just right and haven’t had impingement issues since. I have a set of 155 to trial but have been happy with the 160 so haven’t gotten around to it yet. I have since gone to 170 on my road bike that feels a lot better than the 175 that I had been using. I am convinced shorter is the way to go, the 150 felt fast but hard to maintain the power as it was unusually short and had to concentrate to maintain constant output. It also stressed my back a lot more but may have not raised the front end enough with the seat going up with shorter cranks. I think everyone is different and only you can feel what is best by trail and error.
My experience with the 155s is they feel too ‘fast’ it’s hard to keep a steady effort and I am finding they fatigue my quads much faster.
Anyone else have these experiences? I have been using them for a year, so it’s not an adaption issue!
I have found since going shorter that my cadence is slowing over time. Have a read here with some interesting stuff.
https://www.powercranks.com/cld.html
Yeh I’ve seen that but tried to avoid a lot of the powercranks stuff as reading both that and what’s posted on here the science is a bit flimsy to say the least.
With shorter cranks and the same cadence are the peak forces higher?
I think the force is similar just I engage for more degrees of rotation generating more power than with longer cranks where you get more of a dead spoke in your pedal stroke.
On place measured me with over 34’’ inseam! I measured again at home and it was still aroun 33’‘. My saddle height is usually around 30’’ on both road and tri bikes. I have “short” arms too so, I don’t think I have good proportions. Do the “long” legs benefit your running? I tend to place higher on the run portions of races and generally a faster runner than the other sports. Hoping the shorter cranks benefit my running legs for IM.