Just some observations, as I was a big believer in short cranks. Switched to 145mm cranks about 7mos ago, then to 155mm about 5mos ago. Initially, the additional drop I could manage in the aerobars, while still opening the hip angle, was awesome. Outside, the aero benefit was 20-30 watts. However, after being on the road a few times, I had to raise the front end a bit to keep my eyes more comfortably on the road ahead. Power was the same with short cranks, only short bursts of speed were harder. The first mile or two running off the bike was a bit more comfortable, in that my hips were looser. Eventually though, the issues, imagined or real, created by using square bottom brackets that never quite aligned the chainrings correctly with the rear cog and front derailleur, made me try the 172.5’s again. I won’t be going back to short cranks.
For me, there is a noticeable gain in power from my foot moving faster in a larger circumference, especially at the 1 and 2o’clock position, and is in my opinion because the glutes come into play a lot more. And besides the quieter ride with the drive train lining up, it feels smoother with a standard BB. My front end did not change, and I am just as comfortable in the aerobars after 4hrs plus as with the 155’s. Running was no different either. My suggestion now for anyone wanting to try shorter cranks would be start with dropping your aerobars as far as you can and still keep your head between your shoulders and comfortably see up the road, without periscoping your head into the wind. Doing this on a trainer is not the way to go. Do it on an empty road. The other thing would be to have your saddle all the way forward, and get a longer stem if you need to. There is a reason a lot of pro triathletes ride with the saddle nose even with or slightly in front of the BB. You can substantially open the hip angle up. If after those two adjustments, you still feel like your hips are tight at the top of the pedal stroke, shorter cranks would make sense. Either way, they are cheap to try, and I learned a good amount on bike setup. Just my thoughts after trying it out for a while.
Interesting…I’m a relative newbie to TT bikes but somewhat bought into the short cranks are better mentality on mine with a 165mm 6750 Ultegra compact. It’s not near as short as the ones you were using and this uses a standard BB, but for me I do feel fresher coming off the bike and my hamstrings no longer lock up and cramp on me like they did on my road bike with a 170mm crank. I don’t think I would go shorter because I know I lose some power on hill climbs. I’m fairly short at 5’7" with a 29 inseam so maybe it just fits me better, who knows…My only question would be if I would gain some power (speed) going to a 170mm crank while being able to maintain my ability to not cramp coming into T2.
you didn’t provide info on yourself, experience, strength, height, inseam.
generally, you use a shorter crank on a flatter course…quicker turnover
more hills = slightly longer crank but obviously staying within the reasonable size…for example i am 32 inseam the max i should use is 172.5 …would never use a 175…
I have long torso, short legs (5’ 10", 29" inseam). I run 155mm Rotor 3d and am very happy with it. I am able to get my position quite a bit lower than I could with the 172.5 mm cranks that came with my bike. I initially dropped to 165 because they were fairly easy to get and then to 155 when Rotor started making the shorter cranks. No issues with drivetrain alignment as the Rotor is Shimano Hollowtech II compatible (my bike won’t take a square BB so the cheap shorties were out anyway).
As far as looking ahead goes, that just takes time to deal with/overcome the neck angles. Every time I went lower it was uncomfortable on my neck until I had enough time in the saddle that it wasn’t uncomfortable anymore.
I went through all this in 2009. 6’1", 34" inseam: 165’s. Tried 155’s and it was a diminishing return as I already had all the drop I needed for a solid position. I’d been on 175’s on both road and tt since the 80’s b/c ‘it was faster to use longer cranks’. For me 165’s were a huge revelation. No pinching at TDC, zero loss from the PowerTap, significantly more aero.
The cadence issue brought up by some is kind of silly, as if they have lost the ability to shift gears? Glad it’s working out for ya!
Kimo: you realize square taper bb’s come in all different widths right? You can fix that chain line quite easily.
Interesting review, thanks. But I think part of the issue is that 172.5s, for someone of your height and leg length, already are ‘short cranks’. Going shorter than that for you is going to ‘extremely short cranks’.
Interesting review, thanks. But I think part of the issue is that 172.5s, for someone of your height and leg length, already are ‘short cranks’. Going shorter than that for you is going to ‘extremely short cranks’.
Just depends on the individual…I’m 1" shorter than him, but have an inseam 2" longer!
A rider selects his cadence, but if you ride 20 mph on 175 mm cranks and wish to ride 20 mph with 165 mm cranks you either will spin faster in a lower gear at less torque or spin just as fast in the same gear at more torque. Something has to change with the lever length changes.
I went to 3 different, and quality (I think), bike shops and none could fix it, in terms of BB width. I agree with above that for taller people, std length is probably right. Seeing short women on 172.5’s though is annoying. Booby knocking away in the aerobars is only amusing for so long.
That could be as I think there is a huge variance even when you measure it with a book between the legs. If I jam the book against my nutz as hard as I can my inseam is 36", comfortably is 34". Either way I don’t think there is any right or wrong, just whatever feels right for that person.
Getting so far forward for me really changes the pedaling dynamics where I feel as if I need to almost push backwards a bit…hate that personally. So with 165’s I actually have to ride a bit slacker to keep my 3 o’clock position feeling the same as it did with 175’s.
I went to 3 different, and quality (I think), bike shops and none could fix it, in terms of BB width.
Do you know if there were trying to fix the issue with your bb only or were they putting different bb’s in? Sadly, the garden variety mechanic in a brick and mortar shop these days seems to be a part time pimple faced high school kid thumbing through a Zinn manual hoping he can figure out what he is doing:/ ’
The important thing is you found out what works for you!
If I jam the book against my nutz as hard as I can my inseam is 36", comfortably is 34".
You’re a funny guy.
Getting so far forward for me really changes the pedaling dynamics where I feel as if I need to almost push backwards a bit. So with 165’s I actually have to ride a bit slacker to keep my 3 o’clock position feeling the same as it did with 175’s.
More seriously, this is an interesting observation.
According to Dr. Coggan, a rider does not select cadence, but tangential (or circumferential) pedal velocity. At a given cadence, a shorter crank arm produces a lower CPV. To get back to the self-selcted CPV of the longer cranks at the same power output requires a higher cadence and a smaller gear.
Point being that CPV is the independent variable. Cadence is a dependent variable. No disagreement with your conclusion of more torque or higher cadence as an output.
When you move forward, steeper seat tube angle, you roll your hips/pelvis forward too. Now, with everything rotated forward, the standard 3 o’clock road position is more around 4 o’clock. If you don’t roll your hips forward, it will feel less powerful and awkward, at least for me
If I jam the book against my nutz as hard as I can my inseam is 36", comfortably is 34".
You’re a funny guy.
Getting so far forward for me really changes the pedaling dynamics where I feel as if I need to almost push backwards a bit. So with 165’s I actually have to ride a bit slacker to keep my 3 o’clock position feeling the same as it did with 175’s.
More seriously, this is an interesting observation.
Yea shorter cranks, if you want to keep some things like BDC constant and 3 o’clock, require some tweaks with the saddle fore/aft and height.
I’m sure thats true, but i meant it more in the sense that the rider is in control of their pedalling. Wether we tend to bike a pedal speed or cadence is immaterial to my comment. Either way the rider decides how fast to pedal and when to shift.