Long Distance Competition/Ultracycling, Randonneuring and Endurance Cycling Do you enjoy centuries, double centuries, brevets, randonnees, and 24-hour time trials? Share ride reports, and exchange training, equipment, and nutrition information specific to long distance cycling. This isn't for tours, this is for endurance events cycling

165mm vs 170mm cranks for Randonnuering

Reply

Old 03-12-19, 08:07 AM
  #1  
friday1970
Senior Member
Thread Starter
 
Join Date: Sep 2012
Location: Brighton, Michigan
Posts: 311

Bikes: Baron Optima LR, '14 Nishiki Maricopa,'87 Trek 330 Elance, 1989 Miyata 1400, '85 Peugeot P8, '06 Giant Rincon

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 84 Post(s)
165mm vs 170mm cranks for Randonnuering

So I have two cranksets lying around in my shed. FSA Omega 170mm with the Megaexo BB, and a Shimano 105 165mm crankset with its BB. The weight differences aren't much. The FSA set is about 150g heavier. I am wondering if the extra mechanical advantage of the extra 5mm negates the extra weight.
Though my legs are shorter than average, I usually don't have any knee problems with 170mm cranks. I originally bought the 165mm cranks based off recommendations because of my shorter stature. For short rides, either set works great. But with a 200k ride, the wrong choice could lead to a longer day near the 100 mile mark.
friday1970 is offline  
Reply With Quote
Old 03-12-19, 12:02 PM
  #2  
rhm
multimodal commuter
 
rhm's Avatar
 
Join Date: Nov 2006
Location: NJ, NYC, LI
Posts: 18,892

Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...

Mentioned: 409 Post(s)
Tagged: 0 Thread(s)
Quoted: 1439 Post(s)
I'd vote for the 165's.

If you want more, here's my thinking on this:

Crank arm length does not seem to matter much. I have come to that conclusion after a lot of experimentation. I found it was easy to get used to cranks as short as 140 mm, and hard to get used to long ones once you get used to short ones. In the course of that experimentation I learned that longer cranks offer no advantage at normal pedaling speeds. If you let your cadence get uncomfortably low (like, when it gets hard to turn the pedals over at all) the leverage of longer cranks will help you get another couple yards up the hill before you start to walk, but that's realistic only in rough off-road situations, not what we encounter randonneuring.

Shorter cranks also have their advantages. The main advantage, I think, is that shorter cranks tend to promote a higher pedaling cadence. So I prefer them for that reason.

I use 165's on just about all my bikes, but 160's on my fixie.

Again, I must emphasize that crank arm length does not seem to matter much. Just as people of all different sizes are able to walk up and down the same stairs, just about anyone can ride 170 mm cranks. It stands to reason that there is an ideal size for each person, and that a smaller person will want shorter cranks, and I'm sure that's true; but there has been very little research into what is actually the ideal size. I have no data to support this claim, but I am convinced shorter is better.
__________________
I put new leather on ruined saddles like Brooks, etc. You can reach me by private message.
rhm is offline  
Reply With Quote
Old 03-14-19, 03:55 PM
  #3  
Salubrious
Senior Member
 
Salubrious's Avatar
 
Join Date: Dec 2012
Posts: 1,211
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
There is plenty of data on this and some controversy. In general, the industry doesn't like to talk about it. But it stands to reason that if frames need to be different sizes probably cranks do too.

Its not so much about power as it is about your knees. Longer cranks mean you have to move your knees more and your knees are the most important part of the mechanism. If you have knee problems you are better off on shorter cranks.

Your inseam says much about what crank length you can handle. I have an inseam of 30" and 170mm is the most I can handle. It seems I'm better off on 165s.

Here's a nice article on the issue:

https://ridefar.info/2017/02/crank-l...ance-cyclists/
Salubrious is offline  
Reply With Quote
Old 03-14-19, 04:22 PM
  #4  
phtomita
Senior Member
 
Join Date: Jan 2018
Location: Redmond, WA
Posts: 339

Bikes: '86 Nishiki Tri-A,'84 Centurion ProTour 15,'16 Trek FX 7.4,'77 Sekai GT2700

Mentioned: 4 Post(s)
Tagged: 0 Thread(s)
Quoted: 115 Post(s)
My inseam is 29.5" and both my road bikes are 165 mm (105 and Ultegra).
Since the R7000 has a shorter 160 mm one, I am looking on getting it someday....
phtomita is offline  
Reply With Quote
Old 03-14-19, 05:52 PM
  #5  
ThermionicScott 
Hammer and tongs
 
ThermionicScott's Avatar
 
Join Date: Aug 2011
Location: CID
Posts: 17,703

Bikes: 1991 Bianchi Eros, 1964 Armstrong, 1988 Diamondback Ascent, 1988 Bianchi Premio, 1987 Bianchi Sport SX, 1980s Raleigh mixte (hers)

Mentioned: 55 Post(s)
Tagged: 0 Thread(s)
Quoted: 1739 Post(s)
Our legs are strongest the closer they are to full extension. This is why it's easier to lift more weight with a partial squat than a full squat. So as long as your saddle is set properly for full leg extension at the bottom of the pedal stroke, the length of your cranks the rest of the time isn't that critical for power output. This is why most of the industry can get away with only making a couple of crank lengths within a narrow range. That said, a person's build or riding style may be factors in why they might favor a particular crank length when not at full extension (for example, a short rider may be annoyed with long cranks that cause their knees to bounce really high on the top part of the stroke, or a tall rider may get that "shoes tied together" feeling with short cranks that don't make use of their greater range of motion.)

It would seem like cranks that are perfectly proportional to the rider's body would be ideal, but I think there are other factors that end up confounding this.

More relevant to the OP, I've used anywhere from 165mm to 175mm on my bikes, but switched from 170mm to 165mm on my rando bike for two completely non-physiological reasons: they were lighter, and negated 5mm of toe overlap. So far, so good.
__________________
Originally Posted by chandltp View Post
There's no such thing as too far.. just lack of time
Originally Posted by noglider
People in this forum are not typical.
RUSA #7498

Last edited by ThermionicScott; 03-14-19 at 05:58 PM.
ThermionicScott is offline  
Reply With Quote
Old 03-15-19, 06:06 AM
  #6  
rhm
multimodal commuter
 
rhm's Avatar
 
Join Date: Nov 2006
Location: NJ, NYC, LI
Posts: 18,892

Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...

Mentioned: 409 Post(s)
Tagged: 0 Thread(s)
Quoted: 1439 Post(s)
Originally Posted by Salubrious View Post
There is plenty of data on this ...

Here's a nice article on the issue:

https://ridefar.info/2017/02/crank-l...ance-cyclists/
Thanks for the link! That is an interesting article, and pretty well sums up the available literature.

Nonetheless, I do not agree, that "there is plenty of data." There are plenty of anecdotes, and plenty of attempts to apply mathematical formulas to anecdotal evidence, but very little actual data. So, for example, Kirby Palm (Bicycle Crank Length Derivation) writes "After much qualitative observation and some informal testing, I have concluded that: The standard crank length of 170mm is optimum for a cyclist with a 31-inch inseam."

"Much qualitative observation and some informal testing"? Why do I suspect he means most bikes come with 170 mm cranks and most people are fine with that, so that must be the right size for average size people? I doubt he spent much time trying cranks that were a whole lot longer, or a whole lot shorter, than 170 mm.

I would like to see the results from experiments using a range of crank arm lengths so wide that there is an actual decline in performance at the extremes. I mean, if there is little measurable difference between 170's and 165's, they should try 150's... and 135's, and 120's, and so on. I would like to see power output, heart rate data, etc, for the full range of possible rider sizes, all of them using a full range of crank arm lengths-- not just the ones commonly available.

I think we can safely assume there is an ideal size crank arm for each rider, and that power or efficiency or something will drop off dramatically when using cranks that are too short or too long. But I have never seen test data that clearly identified what is "too short." I assume that even for tall riders it will be much shorter than 165 mm; but that assumption, along with all the other assumptions, really should be tested.
__________________
I put new leather on ruined saddles like Brooks, etc. You can reach me by private message.
rhm is offline  
Reply With Quote
Old 03-15-19, 11:03 AM
  #7  
Salubrious
Senior Member
 
Salubrious's Avatar
 
Join Date: Dec 2012
Posts: 1,211
Mentioned: 8 Post(s)
Tagged: 0 Thread(s)
Quoted: 141 Post(s)
Originally Posted by rhm View Post
Thanks for the link! That is an interesting article, and pretty well sums up the available literature.

I think we can safely assume there is an ideal size crank arm for each rider, and that power or efficiency or something will drop off dramatically when using cranks that are too short or too long. But I have never seen test data that clearly identified what is "too short." I assume that even for tall riders it will be much shorter than 165 mm; but that assumption, along with all the other assumptions, really should be tested.
Its pretty well known that if you have short cranks you can increase your cadence, not unlike what happens in a reciprocating engine.

I don't think power is the big deal here though. There have been some studies that show that the power output only varies by a few percent but the internet being what it is, I can't find the studies that I read ten years ago. The big deal is actually joint injury. This probably won't happen on a shorter ride (600km) but if you go on a longer ride its a common problem which shorter cranks do address. That is how I found out that I can't do 175s- I feel it as soon as I get on a bike using them. If I try to go longer distances (500 miles over several days) I get knee problems. Going twice that distance with 170s no problems at all. A person well-versed in this is Mark Stonich of Bikesmith Design- he's been shortening cranks for many years.

My GF is 5'3" and has the shorted frame Trek makes- but amazingly it is equipped with 170s which seems obvious are too long. She's had knee problems for many years and so doesn't do longer rides anymore. I pointed out the issues with longer cranks and she got a shorter set- no more knee issues! I know its anecdotal, but this idea has been around a long time. However, in doing a search I ran across this:
https://www.stevehoggbikefitting.com...gth-which-one/
Which has some very interesting comments, very nicely explained.
Salubrious is offline  
Reply With Quote
Old 03-15-19, 12:23 PM
  #8  
rhm
multimodal commuter
 
rhm's Avatar
 
Join Date: Nov 2006
Location: NJ, NYC, LI
Posts: 18,892

Bikes: 1940s Fothergill, 1959 Allegro Special, 1963? Claud Butler Olympic Sprint, Lambert 'Clubman', 1974 Fuji "the Ace", 1976 Holdsworth 650b conversion rando bike, 1983 Trek 720 tourer, 1984 Counterpoint Opus II, 1993 Basso Gap, 2010 Downtube 8h, and...

Mentioned: 409 Post(s)
Tagged: 0 Thread(s)
Quoted: 1439 Post(s)
All in all, @Salubrious, I think we agree. My wife, who is much smaller than I, and does not have disproportionately long legs, rides a 650c bike with 170 mm crank arms. Her bike is tiny, really looks comical next to one of my bikes., but it has longer crank arms. I am reluctant to shorten them, because (a) she likes them, and (b) if I shorten them* then I would have to raise her saddle by 17 mm or so, which she does not want.

(*Shortening them is not a problem; I have a 175 mm crank that is otherwise the same as what's on her bike, and I have taps etc for shortening it. I could safely cut the 175 mm crank down to 153 mm or so (or shorter). I've done this several times.)

Let me rephrase something. I subscribe to the principle that the ideal crank length should be proportional to some bodily measurement. I am not convinced it is inseam; maybe it's femur length, I don' t know, I haven't studied this. The reason I reject the usual recommendations is that they are based on an assumption, or the narrow range of crank arms that is readily available, rather than a full range of theoretically possible crank arms.

By "ideal crank arm length" I mean the crank arm length that gives the best compromise between power, efficiency, comfort, wear and tear on the body, or any other factor that might seem relevant. Given that the choice is between 165's and 170's, I think it important to emphasize that there is not much difference between them. I am convinced the shorter of the two is better; but I am not convinced it is shorter enough.

Ten years ago I read an interesting study on the internet, in which the tester had had several different riders try out cranks ranging from 140 to 180 mm, if I recall correctly. I cannot find this article any more. The result was that all riders strongly disliked the shortest crank arms at first but soon became accustomed to them and stopped complaining; but when they went back to longer crank arms, they strongly disliked the longer ones, and it took longer for them to stop complaining. As for power, speed, comfort, etc, there was not much difference among the crank arms tested. Logic would dictate that they repeated the experiment with shorter and even shorter cranks (as well as longer and longer ones), but i don't know if they ever did that.

Mike Burrows and Mark Stonich --both of whom have an interest in recumbent bikes-- are both proponents of shorter cranks, both for recumbent riders and for the rest of us.
__________________
I put new leather on ruined saddles like Brooks, etc. You can reach me by private message.
rhm is offline  
Reply With Quote
Old 03-24-19, 09:32 PM
  #9  
friday1970
Senior Member
Thread Starter
 
Join Date: Sep 2012
Location: Brighton, Michigan
Posts: 311

Bikes: Baron Optima LR, '14 Nishiki Maricopa,'87 Trek 330 Elance, 1989 Miyata 1400, '85 Peugeot P8, '06 Giant Rincon

Mentioned: 1 Post(s)
Tagged: 0 Thread(s)
Quoted: 84 Post(s)
Originally Posted by rhm View Post
Mike Burrows and Mark Stonich --both of whom have an interest in recumbent bikes-- are both proponents of shorter cranks, both for recumbent riders and for the rest of us.
On my recumbents, having smaller cranks do seem to relieve stress on my knees far more than longer cranks do. I was running 155's, now 165s, and I might go back.

But on my road bikes, my 170's seems to be OK. I can usually find a gear combination to allow me to do 95-100 rpms. I might stick to this size simply because most of the brevet routes around SE MI tend to be rolling terrain, and I could use the mechanical advantage going up hills (especially at my weight).
friday1970 is offline  
Reply With Quote

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service