I wouldn’t worry too much about ultegra vs. 105. The technology trickles down such that the 105 of this year is just as good or better as the ultegra or dura ace of a few years ago (maybe “better” because the kinks have been worked out).
In other words, ultegra might be better but 105 is still very good
I went to a bike fitter complaining about being able to stay in aero bars - he made adjustments and tried me on shorter cranks. It ended up getting shorter and shorter and it didn’t make much difference to me in terms of feel (he’d said some people complain of feeling like they’re doing minature circles like a circus clown). I’m very happy with the change - so much so I just ordered another crankset to match my road bike with my TT. Estimates = 5’6’" tall, 30"inseam; I’m using crank length 145. Cobb cycling sells standard, compact, mid-compact w/ a range of crank lengths.
I take the position that my bike will always be better at cycling than me. Shimano 105 is probably better than I am.
Especially if you replace just the crank arms and keep the rest of the Ultegra setup. Unless you’re a real weight-weenie, it’s not like crank arms are high-tech
@Jon @Sir_Brian_M Coach always used to say that people will spend hundreds of dollars to shed grams off their bikes when it costs little to nothing to shed pounds (kilos?) off their backsides…
Well, not quite sure what you are trying to say here. Considering that my issue is too great of a knee bend at the top of my pedal stoke, my only options are to live with it or replace my crank arms. Losing weight won’t solve this.
Besides, I weigh 160lbs. At 5’7” tall, with a 32inch waist, there is not much more weight I can safely lose. I’ve already put in the effort to lose the weight. I used to weigh 192lbs in 2014 when I bought a bike shaped object at Walmart to get in shape.
I’ve come a long way since then, and worked hard to get where I am today. I would venture that everyone on this forum could tell a similar story.
So with that in mind, if all I needed to do in order to fix the fit issues on my bike was to lose a few pounds, I would not have bothered asking the question about changing my crank length.
Oh, nothing directed at you @Sir_Brian_M. Apologies for any misunderstanding! Was just taking a tangent on the Dura Ace - vs - Ultrega - vs- 105 riff.
Very sorry!
(FTR, your story is REALLY impressive. Getting back to the bike after a 20+ year hiatus, I only hope I can compare down the road).
Agreed, the amount of money one can throw at their bikes to save a few grams is a bit mind-boggling.
And whew! I’m glad I misunderstood you.
I have been considering shorter cranks, and am the same height and inseam as the OP. My local bike shop has been super helpful and put a set of old, Serotta adjustable fitter cranks on my bike, and I have been experimenting with the different crank lengths on my trainer. I do notice a difference in ability to spin higher cadences (better with shorter cranks, I’ve gone down to 155 from 170 mm), but I’m still getting used to using different muscles with the short cranks. Anyway, if you are able to get one of these fitter cranks, it is an awesome way to try things out before committing.
My LBS said they can’t get oem parts. They are back ordered indefinitely. They suggested looking on eBay/Facebook etc. last night I found a 105 160mm crankset on eBay.should arrive next week!
You’re not kidding. Power Meter maker 4iiii is buying used Shimano left crank arms so they can convert them into power meter cranks.
My new crank arms arrived yesterday. LBS did a rush job to get me setup for my ride today.
Oh my! What an amazing difference. Smooth at all cadences between 80-160 rpm. My cycling dynamics power curves are now nearly symmetrical, while slightly favoring my left leg for power output.
And here’s what it was with the old cranks.
@Sir_Brian_M Sorry to open up and old post. Wondering if you had an update on how the shorter cranks are going. I bought a new road bike this summer and it has 172.5mm cranks when I used to ride the 170s. It is a whole heap of difference. The crank length calculators I have found all seem to suggest 165s. I have found this thread interesting and I’m pretty sure I’ll go short, just wondered how you were getting on with them after the last update on May 22. Cheers
I love my shorter cranks, 160mm Shimano 105 crankset (only because Ultegra doesn’t exist). My NM dropped a bit, but I spend so little time there that I’ll happily take the improved pedal stroke.
Late in the season, I typically see PRs on frequented routes, but I’ll attribute some of that to the shorter cranks. Just this past weekend, I averaged 29.2 mph for a half mile segment while riding into a 10mph partial headwind. Not sure the actual vector, but suffice it to say, I’m pleased with the result.
I’ve got more power in the drops and can hold it for longer. Also nagging issues with my ankle joints have disappeared entirely.
Thanks for the update. Good to know. My kids all had 152/155 cranks on their bikes growing up. My son who has longer legs than me went to 170s (borrowed his Mama’s bike) and now has same size bike as me with 172.5mm cranks and he has no problem. He is young and flexible with size 45 feet (mine 42) and a longer inside leg bizarrely, even though he only a couple on cm shorter than me. He spins away nicely. Something odd clearly happened in the genetics. I got super short legs and feet, he got super long ones.
I get hip pain and knee pain going over the top of the stroke. Who could imagine 2.5mm would make such a difference. Looks nothing on a ruler. Will certainly look out for 105/Ultegra 165mm. At 52, I’m not getting any younger and the discomfort from longer cranks has been disturbing. I do find I prefer spinning anyway to grinding. Thank you so much again for the update.
Based on some randomly Googled on-line calculators, my optimal crank length is either 170 or 172.5 and I have 175’s. I’m just a hair until 5’11", and I’ve considered switching to 170 or 165. But, I would actually have to find some, first. And they’re aren’t cheap. I need new front rings, so now would be a good time. If I can find them. I’m just not sure if I want to drop all the way to 165. I may have to do the same thing as you did and get 105’s instead of Ultegra. 
Ultegra comes in 165 through 175. I have 160 105 crank arms.
If you go to a fitter that has a Retul they can easily change the crank lengths and see how it effects you. From past experience many fitters look at crank length last as it is very hard for them to adjust to see how it impacts your fit, and very expensive for you to buy just to try.
FWIW: my new bike is coming with 165’s.
