get both and "test" them for a few months, with the help of your "coach"

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Swimming Workout of the Day:

Favourite Swim Sets:

2020 National Masters Champion - M50-54 - 50m Butterfly

So tempting!
But alas, I have no velotron and thus cannot accumulate vast quantities of "data" in the correct way.

I think I'll have to just choose one and ride....

So let's have a vote.

Pick a number guys!
160 or 165?


[Edit] Not that there's much consensus that it matters, but I'm 1.78m (5'10) with an inseam of about 840mm. My saddle height is 745mm measured from BB to perch (not vertically) while using 172.5mm cranks.

At the recommendation of Dave Luscan I went to 165mm from 172.5 this winter. Has worked pretty well for me; going down to 160 is almost the same difference again and I think (for whatever that means) that would have been too much.

Main experience is better able to produce power in aero, and higher preferred cadence when doing so. On my road bike, and with the longer cranks on my P4, I'm at 75-80rpm, and now with the shorter crank I'm at 85-90rpm.

YMMV, but I would go with 165.

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Citizen of the world, former drunkard. Resident Traumatic Brain Injury advocate.

I bought 155 rotor cranks last year. I am 184cm tall (6'1). I used them to get a better TT position without closing my hip angle. I alternate between my TT bike with 155's and my road bike with 172.5 and don't notice a massive difference in feel when I swap between the 2 bikes. I haven't found any downside to the 155's but they definitely got me lower on the TT bike. I figured if I'm going to experiment going shorter then might as well go as short as possible. They don't feel that much different when I'm riding and I spent all winter riding them on my bike trainer.

BTW, I bought mine from an online shop in France " Velo-perso". They were a lot cheaper than buying them in the UK.

Thanks Tubs
I just checked out Velo-Perso. Similar price to Bike24 in Germany where I was looking, but good to know they're there.

I am in the exact same boat. 6'2", Went to Cobb 155's from 175's after a bike fit from Chris Balser. Crank length allows the hips to open up and I'm extremely happy with the decision. Additionally, going back to the 172.5s on the roadie is seamless.

Ai_1 It's super hard to make this recommendation via text. The best would be to have you in my fit studio, on my dynamic fit bike and we'd make changes with the position and crank length and come to a decision together. I guess the next best thing would be a video, at profile, of you riding to see your current position on the 172.5s. If we had to continue in text I'd ask this - what is your handle bar elevation (with bike level, rest a long level on the center of your saddle and let it hover level over your arm-pads - what's the gap down to your arm-pads)....and....are you comfortable with that "drop"? Specifically does your hip feel cramped or pinched at the top of the pedal stroke, does your thigh hit your belly, etc.

From that we could make a more accurate assumption as to which would be better 160s or 165s.

Ian

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Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan

In my opinion/experience, a large part of the answer to that question comes down to the individual mobility of the cyclist.

Muscles operate most efficiently over their full range of motion and the energy cost of being on the wrong crank isn't insignificant (even when the cyclist can't really 'feel' the difference).

Based on the testing I've done on myself and others, the O2 cost can be 5-10% greater for the same power output when the cyclist is on the 'wrong' crank.

A few more thoughts here...

https://www.alancouzens.com/blog/crank_length.html

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Alan Couzens, M.Sc. (Sports Science)
Exercise Physiologist/Coach
Twitter: https://twitter.com/Alan_Couzens
Web: https://alancouzens.com

This thread might be helpful:
https://forum.slowtwitch.com/...0bio-mcgeek#p6507911

I'll just paste it for easy access.
Hello All:
In other current threads there appear to me to be attempts to market adjustable cranks by one particular seller. These are thinly veiled under the pretext of trying to help one particular forum member find the best length for him or her.
I am writing this to point out that there are several options available to anyone who wants to experiment with different cranks. Most obviously, one might visit a fitter with an adjustable crank system. For the do it yourselfers, there are several options as well. One easy option is to use crank shorteners which are typically sold so kids can ride on tandems with their parents. $135-145 from Tandems East or one by SJS at 65 British Pounds. These would allow you to find the length you like and then buy fixed length cranks from Cobb or other sellers of novel lengths. Adjustable cranks are made by SRM, High Sierrra, and Purely Custom ($449). With these too, you would find the length you like and then buy regular cranks in that length. Another approach would be to buy two or three lengths of Origin8 or Sinz which sell for only $50-60 per pair. The downside to these is that they are mostly available for square taper bottom brackets (which I still ride myself). So, if you want to experiment with length, there are lots of options from reputable companies.
Cheers,
Jim

Shorteners:
http://www.tandemseast.com/parts/cranks.html
https://www.sjscycles.co.uk/...-right-each/?geoc=US

Adjustable cranks:
SRM: http://www.srm.de/...rmeter/science-road/
High Sierra: http://www.hscycle.com/...ustablecrankset.html
Purely Custom: https://purelycustomfit.com/...-bike-sizing-cranks/

Origin8. These are listed as single speed but the two pair I bought were doubles: https://www.amazon.com/...words=origin8+cranks

I'm riding 155 on the tri, 165 on the gravel, 172.5 on the road, and 175 on the mtb. I also do not own a fleet of velotrons, but I can't tell the difference

Oops, too late. I ordered 160mm cranks before seeing your post. Although I could return them unused.

I'm pretty comfortable with the 172.5 cranks but reckon I'd be moreso with something shorter. My hip angle feels a bit pinched in aero position and I feel my knee angle is excessively tight at the top of the stroke.
I think my saddle to pad drop is about 70mm but will need to check. I have the pas inclined about 15deg so my elbow is probably more like 80mm drop.

My tri bike currently has a 170 on the drive side and 165 on the other (long story). When I am riding, I can't tell the difference. If I could find a decent crank that did not have a wide q factor in 150mm, I would go the Jens route and go much shorter and narrower.

Chad

"Hip feels a bit pinched.....70mm of pad drop" - sounds like you made the right call with the 160s.

Ian

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Ian Murray
http://www.TriathlonTrainingSeries.com
I like the pursuit of mastery
Twitter - @TriCoachIan

Thanks AC. Always helpful.

Something something Velotron.

If you can go 160/155 then try that... I am 5'11 and have a saddle height of 75.5 & I'd love to be on a 155!

If anything get a 155mm then if it doesn't work we can trade as I have a 165mm just make sure it is a 24mm spindle crankset 😉😉😉

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Speed kills unless you have speed skills!!!

actually there is a way to test shorter cranks: cut cheap cranks short!
no, that’s not a joke, i found a bike-shop in germany that does exactly that (http://www.ramlon-bikes.de). it’s not that hard at all from an engineering point of view. you cut the crank, drill a hole and cut in a new thread: voila, your short crank. any decent workshop/garage should be able to do it.
the cranks do have to be solid of course (! many are not to because of weight !), but if it’s for testing, any kind should be ok. so talk to your lokal bike shop, have them prepare 3 different legths and give them to their customers to try out.
here’s a picture of a custom 145 mm sram apex crank on my bike. i bought it used and had it shortened.



cheers,
dan

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then someone will say, what is lost can never be saved.
despite all my rage, i am still just a rat in a cage.
- smashing pumpkins: "bullet with butterfly wings"

You don't have to go all the way to Germany. Mark in MN does a great job!

http://bikesmithdesign.com/

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No coasting in running and no crying in baseball

Thanks, but fear not! I didn't intend to hold myself subject to a democratic vote on the issue. Interested to know what STers thought but I don't and never have weighted all opinions equally. Arguments on merit, assertions on logic, evidence and experience. Typically but not universally in that order.

I've put a bit less thought into this than most of my purchases (I'm prone to procrastination on these things) but I'm reasonably confident in my choice.

I have previously had a good look at the subject and have read previous contributions by a number of experienced fitters including those you've mentioned but never managed to decide which length was the prudent one to try.

while i have no quarrel with what you're saying, alan, there is a chasm of context you're leaving out, for the purposes of this discussion, like you answering my question, "is it appropriate for me to beat my wife..." ignoring the rest of the question, "...in tennis."

your article to which you link does include one sentence in which the context is placed, "a crank length that is on the long side will also prevent an athlete from rolling the hips forward into an effective aero position and will actually cost them a not insignificant amount of speed!"

this is what differentiates proper crank length in tri or tt, from road (or gravel or MTB) where you're not constantly finding, with every pedal stroke, the limits of mechanical advantage.

somewhere in nature lurks the unifying theory of everything (in tri/tt bike position), where mechanical advantage, efficiency, aerodynamics and crank length live as values, and if you change 1 value you change the rest. if you change the crank length on your gravel bike you probably don't change the aerobar elevation. but on your tri bike, you do, if you want to normalize that bike for hip angle at TDC.

so, i'm cool with everything in your statement. still, the statement is short on the implications of crank length in tri versus in other cycling disciplines. that's why crank length, as a variable, is constantly on the table in tri: because you're up against a hard limit on mechanical advantage and aerodynamics with every pedal stroke.

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Dan Empfield
aka Slowman

Thanks Dan,

Your response brings back a very fond memory of you, me and Mat hanging out in Gordo's basement engaged in deep, friendly argument over the role of mobility in bike fit. Very good times.

Unfortunately, in this case, it's with deep regret that I have to say I am in complete agreement with what you've written above.

With a couple of minor additions...

1. In triathlon, especially long course triathlon, for the vast majority of folks on the course, I would suggest that, with less than stellar natural mobility going in, coupled with mean race durations of 12hrs and bike speeds of ~30km/h, efficiency greatly trumps aerodynamics when identifying the optimal position in that 'chasm of context' that you're talking about. This is not reflected in fit marketing ('cause it's not as sexy as taking out more spacers :-)

2. This 'balancing' of important factors that you're talking about rarely happens in a real world bike fit. IME, fitters are either over-fixated on aerodynamics to the exclusion of individual efficiency or, (less commonly) focused on coming up with a comfortable fit without assessing the aerodynamic cost. I have a hard time coming up with a name of a fitter who does both well. I know some sports medicine/physio guys who are very cluey on the comfort/*bio-*mechanical efficiency side and some 'wind tunnel guys' who know the ins and outs of a truly aero fit but there are few who do a complete job of balancing the 2 IMO.

Frankly, it blows me away that in this day and age, most fits are being done without any actual data collection on either side of those equations, i.e. aerodynamic or physiological 'cost' of various positions.

As you suggested above, the answer to the 'right' crank length for an individual surely lies in collecting data from those metrics to come up with the optimal 'balance-point' for each individual.

Thanks, once again, for some great dialogue.

AC

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Alan Couzens, M.Sc. (Sports Science)
Exercise Physiologist/Coach
Twitter: https://twitter.com/Alan_Couzens
Web: https://alancouzens.com