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-   -   crank length (https://www.bikeforums.net/showthread.php?t=1095800)

Squeezebox 01-25-17 09:27 AM

crank length
 
I'ld be interested in your opinion/experience with different crank lengths. Including how that relates to cadence, and power output (measured or not), comfort, etc.
Someone fairly casually mentioned the subject. I'ld like to hear more.

Squeezebox 01-25-17 09:42 AM

My carbon road bicycle is 172.5 . My touring bicycle is 170. The around town 7 speed 170 also. And I did have a track bicycle with 165 cranks.
Each bicycle handles so much differently that I don't think that I can tell any great difference in crank length. Maybe with the track bicycle, but fixed gear is so much different. I also had a road bicycle to fixed conversion, no markings on the crank. was the difference fixed gear or crank length? I wish I had the extra $$ to try out 180 cranks on the touring bicycle. But alas. I'm 5'8" with 52 cm bicycles.
So what's your opinion and/or experience?

mstateglfr 01-25-17 09:43 AM

I have 170 and 175. I am 6'5. I couldnt care which I use. I am not a refined enough rider to care about 1cm of difference in my pedal stroke and since neither is too long for me, its not like my hips will hurt.


You have been riding for 3+ decades and have road bikes, town bikes, and a zombie killer. You have toured Europe and locally. I am sure you have enough experience to share too- what have your crank lengths been and how has it affected your riding?

Wilfred Laurier 01-25-17 09:46 AM

Over the past couple years I have used 170s, 175s, and 180s. There is a minor difference in how comfortable it is to spin at med/high rpm, but that might be partly because I have spent decades road riding on 170s without giving it much thought.

indyfabz 01-25-17 09:47 AM


Originally Posted by mstateglfr (Post 19335092)
you have been riding for 3+ decades and have road bikes, town bikes, and a zombie killer. You have toured europe and locally. I am sure you have enough experience to share too- what have your crank lengths been and how has it affected your riding?


+1.

indyfabz 01-25-17 09:50 AM


Originally Posted by Wilfred Laurier (Post 19335105)
but that might be partly because I have spent decades road riding on 170s without giving it much thought.

I don't even know the length of my inferior steel LHT crank arms, but I am guessing 175 since it's a 60cm frame.


Franky, I simply tour (and have evidence to back it up) without worrying much about stuff.

bradtx 01-25-17 10:06 AM

@Squeezebox, I've used 170, 172.5, and 175 mm crank arms. I spec'd 172.5 mm for my builds and currently only have 170 mm and 175 mm crank arms.

Comparing 170 mm to 175 mm crank arms on two very similar bikes, I can spin up my cadence higher with the 170s and although there is a leverage advantage using a longer crank arm, it isn't something that I can feel. FWIW, both of my touring bikes have 170 mm crank arms.

Brad

GamblerGORD53 01-25-17 10:12 AM

The facts are .... There is a 3% power diff for 5 mm length. Usually it is only noticed with an IGH like a SA hub with big gaps. I went from 165 to 180 and it changed everything to the better. Comparing these at the same speed, the shorter one will do 100 rpm while the 180 will do 91. BUT the relative circumference speed will be EXACTLY the same. Newton's second law. Knee extension is worse for higher, but offset some by less downforce.

I find the shorter one is gutless. I am 5'8". Tour bikes are mostly using 175s now, not bad.

fietsbob 01-25-17 11:27 AM

At a modest cadence, 170, 175, 180 are all fine. 180 lets the saddle come down
that 5 or 10 mm, Vs, the shorter...
while maintaining the same saddle top to pedal distance.

Standing on the pedals, climbing hills, there is the Leverage to consider..
Plus there is the frame BB height..

so the Low BB on my Brompton has 170 cranks.
Higher BB on The Koga, has the 180..

it also gave the illusion of more saddle setback,
then I bought a different seat post.



...

McBTC 01-25-17 12:04 PM

There are studies showing, for example, that 145s are more efficient than 175s but confirming such findings in your own situation is difficult. You can experiment with inexpensive crank shorteners but they change the Q-factor and even if you were to bite the bullet and purchase new cranks, you'd need to raise your saddle by more than an inch which will put you into an more aggressive riding position if your current setup prevents you from easily raising and possibly bringing back your bars. Going with shorter cranks makes it a lot easier to pick up your pace.

robow 01-25-17 12:30 PM

Shimano presently offers their road cranks in 4 sizes ranging from 165 to 175mm. Think about the fact that this small 1 cm range is designed to serve humans that are 5 ft tall and those that are 6.5 ft tall. Obviously there is a lot of leeway here. Many years ago when I was buying stock bikes, a size 56 frame sometimes came with 170 cranks and other times with a 175, there was no 172.5 at the time. I became accustomed to 175's on my mountain bikes and so over the last 20 years when I build a frame up, I use 175 but I'm sure that I can't tell the difference in 2.5mm,.... 5 mm maybe?...wouldn't want to bet my life on it. A few years ago I changed out a bottom bracket for a friend who had over 20,000 miles on a bike after just a few years, and when I went to remove the cranks, I noticed he had two cranks arms of different lengths and yet he had never realized the difference. Ha

McBTC 01-25-17 12:34 PM

1 Attachment(s)
* http://www.ncbi.nlm.nih.gov/pubmed/11417428

indyfabz 01-25-17 12:45 PM


Originally Posted by GamblerGORD53 (Post 19335167)
The alternative facts are ....

fify ;)

phughes 01-25-17 01:18 PM

I changed from 175 to 170 on my LHT over the Summer. I much prefer the 170s. I spin more easily. With the 175s I felt too much of an on/off sensation on each revolution. I was dealing with a nagging fit issue on this bike as well. I am sort of between frame sizes and opted for the 56 over the 54. The 54 comes with 170s so I decided to try them. I am more comfortable on the bike with the shorter cranks. It was a good change for me on this particular bike, for the way this bike is ridden. I sit and spin up hills and don't get out of the saddle. I also increased my speed a bit on flats as well. YMMV but for me, it was a good change.

Many moons ago, I raced BMX with 165s.

tarwheel 01-25-17 01:23 PM

Are you a spinner or a masher? I would presume that spinners would prefer a shorter crank and mashers a longer one. Your height, leg length and frame size are other relevant factors. In my case, all of my bikes have 172.5 cranks. When I buy a new crank, I search until I can find a 172.5. My knees are very susceptible to small changes in saddle height, so I would rather not mess with a good thing. I know that 172.5 fits me just right, so why change? However, 172.5 cranks are getting harder and harder to find as manufacturers limit their product lines.

bwgride 01-25-17 03:11 PM

Sheldon Brown

http://www.sheldonbrown.com/cranks.html

LeeG 01-25-17 04:37 PM

I like my cranks to be the same length

Brett A 02-19-17 10:27 AM

I went though this question as I was setting up my first-ever touring bike last summer in preparation of my first-ever tour; a 4 week/ 80k feet climbing solo, self-contained tour from Sebastopol,CA to the North rim of the Grand Canyon via Yosemite, Death Valley and Zion National Park.

The bike came with 170s. And over the summer, for may overnight camping rides from the house, I tried 172.5 and 175s. All with the same size granny (a 26)

Even though, after 30+ years of riding, I am used to 175s on my mountain bike, and 172.5s an my road bike, I wet with 170 for touring for two reasons that make sense intellectually and experientialy.

A shorter crank requires less articulation of the knee joint (it doesn't open/close as much on each cycle). And, since a touring bike is ideally geared in a way that does not require a lot of force on the pedals, 170's are just more comfortable and, in my estimation, safer on the joints. (Now that I'm 50, that is more of a concern)

I ended up with a 22/36 low gear combo with 26" wheels. This is about 15.5 gear inches which allowed me to climb the Sierra Nevadas, etc. on a fully loaded bike without going above a conversational effort, climbing at about 3 to 4 mph at around 80rpm. Point here is that at such easy effort, crank leverage is a non-consideration.

So I'd recommend 170s from my experience.

dabac 02-19-17 10:43 AM

I do find it easier to maintain a higher cadence with shorter cranks. That was important to me when my knees were giving me trouble.
Before and after, it didn't matter much.

I am a tad bit faster on longer cranks. But tend to be sorer after.

shelbyfv 02-19-17 11:24 AM


Originally Posted by mstateglfr (Post 19335092)
You have been riding for 3+ decades and have road bikes, town bikes, and a zombie killer. You have toured Europe and locally. I am sure you have enough experience to share too- what have your crank lengths been and how has it affected your riding?

:roflmao: Actually, it's over 40 years ......

robow 02-19-17 11:41 AM


Originally Posted by dabac (Post 19388374)
I do find it easier to maintain a higher cadence with shorter cranks.

Do you think that such a small difference in crank length, less than 3% from a 175 to a 170mm affects your cadence more, even though you will still be turning the same number of gear inches, or going one gear lower, which can often decrease gear inches by 15% allows for a higher cadence? I'm going to bet on the latter.

36Oly_Rider 02-19-17 12:14 PM

Not sure where I saw it... may have been GCN or something... but wherever it was, it was said that on the flats, you really won't notice the difference between different sized cranks, but you'll benefit more from the shorter ones going uphill.

dabac 02-19-17 02:07 PM


Originally Posted by robow (Post 19388500)
Do you think that such a small difference in crank length, less than 3% from a 175 to a 170mm affects your cadence more, even though you will still be turning the same number of gear inches, or going one gear lower, which can often decrease gear inches by 15% allows for a higher cadence? I'm going to bet on the latter.

The OP asked about opinion/experience, not data verified from double-blind testing.
And those are mine.
You are welcome to yours.

IMO humans can be surprisingly sensitive to changes in bike/rider interaction.
Sometimes the change in feel influences the rider's effort to create a greater difference than physics/mechanics only would suggest.

I have a long history of achy knees.
I kept trying to train myself out of mashing and into spinning.
But as soon as I didn't actively think about pedalling technique, I kept upping the gears and dropping the cadence.
That is, until I went to shorter cranks.
That kicked my average cadence up with 10, w/o me having to think about it.
And my knees stopped aching as often.

For me, there's just something about the feedback from longer cranks that makes me opt for a higher gear, a harder push and a lower cadence.

The pattern still stays true. I've got bikes with different crank lengths, and I always get a higher average cadence on the shorter-cranks bikes.

IK_biker 02-19-17 10:08 PM


Originally Posted by GamblerGORD53 (Post 19335167)
The facts are .... There is a 3% power diff for 5 mm length.

Wrong.
There are no such facts in evidence.

GamblerGORD53 02-19-17 11:06 PM

Maybe I used the wrong terminology BUT ... Pedals ARE levers >> Power or work = F x D.
Math is math. There is nothing wrong with my math as stated. 5/ 165 = 3%.
You can wizz around all the hell you like with 18 GI or whatever, I will prefer 75 avg rpm.
What is gained in force is lost in distance.

You noticed that Usain Bolt won 9 gold medals with LONG strides??


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