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165mm vs 170mm cranks for Randonnuering

Old 04-30-19, 11:35 AM
  #26  
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Originally Posted by ThermionicScott View Post

P.S. Now that you bring up BB height, I wouldn't be surprised if part of the reason for the industry standardizing on 170mm cranks is to fix that aspect of frame manufacture, rather than needing to offer a zillion more frames with varying BB heights. If a bike company were sympathetic to the need for a wider range of crank lengths, perhaps they could scale the BB height with the frame size. Maybe some makers do already...
My GF complains often that she can't put a toe down to balance herself on any of her bikes. She has to get off the seat at a stop. This is because even though she's on the shortest Trek frame made, its bottom bracket is the same height as mine. The industry really doesn't support shorter people wanting to ride bikes. Some of this has to do with wheel sizes and how geometry changes affect handling; but to me it just sounds like they don't want to do the harder work of figuring it out.
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Old 04-30-19, 12:15 PM
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the industry is deathly afraid of pedal strike. Sure, it can be dangerous in extreme cases, but it usually isn't that bad. I have a whole collection of vintage pedals with the bottom outside edge totally messed up. I have never gone down due to pedal strike
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Old 04-30-19, 06:27 PM
  #28  
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Originally Posted by rhm View Post
<snip>On the other hand, I'm pretty confident you could switch your wife's crank onto your bike and you'd get used to them in a short time and get to like them just fine. But it's a tandem stoker crank, and the pedal threads will be backward, so never mind that.
<snip>
You often mention that it's important to spend some time out of the saddle on all rides (I hope I'm not confusing you with someone else), and it's good advice. Shorter cranks do tend to discourage the rider from getting out of the saddle, and that's not a good thing. Anyone investigating 'ideal crank arm length' would need to keep this in mind. Whatever the ideal crank arm length is, it's going to be a compromise.
So far I haven't ridden a tandem on which normal L and R pedals didn't fit all 4 cranks normally. Specially threaded tandem cranks may be ancient history. In any case, I already spin 100 comfortably on the 175s, and am not about to give up the OOS leverage or the steep stuff seated leverage. I don't see what shorter cranks could improve.

We've now ridden a couple hundred miles with the 151mm stoker cranks. It became obvious that we were much slower on steep climbs where our cadence dropped below ~80. On the good side, Stoker likes them. On the bad side, she's cramped more with the shorter cranks, something I did not expect, but because of the shorter lever arm, she has to push down harder on the steep stuff to produce the same power. On the good side, she can stay up a little longer when we stand. On the bike mods side, I've put a 40T cassette on, so now our lowest gear is 26 X 40. That gets us up the 15% grades we could not climb with the shorter stoker cranks and a 34T cassette.

On our tandem, captain's ratio is 5.56 and Stoker's is 5.59. On my single, my ratio is 5.40. Stoker's previous ratio was 6.30.
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Old 05-27-19, 02:45 PM
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Iím never riding anything shorter than 200mm cranks again if I have a choice.
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Old 08-16-19, 01:22 PM
  #30  
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Just did conversion #4 to short cranks. All for friends. In each case warned that it was pure guesswork. Three of four had very short test rides on a non-ideal test bike. Each rider is completely amazed at how well 150 or 152 cranks work. For them. Promising it will work for you would be silly. But if you are curious or have any reason to think you are a good candidate for shorter cranks it is worth a try.
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Old 08-18-19, 06:15 AM
  #31  
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For an extreme long crank argument, check out this 1969 Bicycling article posted in the C&V forum: https://www.bikeforums.net/classic-v...-magazine.html

For what itís worth, Iím in the short crank camp because my hips arenít very flexible. With 170s I have a hard time getting over the top of the pedal stroke when Iím on the drops because my hip canít close far enough. The natural tendency is to compensate by rolling the pelvis pack and bending with the spine rather than hip, which isnít good for the lower back.
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Old 12-03-21, 10:08 AM
  #32  
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Coming to this thread late. I was stressing about a difference in 5mm over crank length until I looked at what the difference looks like on a tape measure. It's about a 1/4 of an inch. That distance looks negligible especial since cleat and even seat height/fore aft might make a bigger difference in knee bend and health vs 5mm of crank.
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Old 12-03-21, 11:56 AM
  #33  
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Originally Posted by Damon216 View Post
Coming to this thread late. I was stressing about a difference in 5mm over crank length until I looked at what the difference looks like on a tape measure. It's about a 1/4 of an inch. That distance looks negligible especial since cleat and even seat height/fore aft might make a bigger difference in knee bend and health vs 5mm of crank.
The difference does not seem like much and in terms of power it isn't.

And a Randonneur often isn't long enough for a knee injury to show up.

But if you compare a longer crank like a 175mm vs a 165mm, then the distance needed isn't so much to do damage to the knees. I've ridden the Tour Divide Race a few times and by the time some riders have gotten to Eureka Montana, their knees were already injured. This usually happens with shorter people, since mountain bikes tend to come equipped with 175s and mountain bikes are the preferred mount on the TDR. Eureka is about 250 miles from Banff by the route, over 5 passes (if Koko Claims is part of the route).

If you already have knee problems, running a shorter crank will allow you to still be effective. I know one woman that had a torn meniscus in her knee and so ran 150s and was able to complete the entire 2700 miles. You spin faster with the shorter cranks, just like in an engine, exchanging torque for rpms. So you might have to adjust the gears a bit if shorter cranks are used.

I run 175s on my Cutthroat on the TDR in 2017; by the time I made Wise River my right knee was shot. Its still sensitive to this day. When I get a new bike I always make sure to install shorter cranks on this account. In 2019 I had no knee problems at all running 170s and I made it a lot further that year- into Colorado.
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Old 12-06-21, 09:53 PM
  #34  
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Originally Posted by antimonysarah View Post
But more seriously, this is the first thread that's made me want to try shorter cranks; I'm 5'5.5" and short-legged (29" inseam men's jeans are about an inch too long), and have been fine on 170-175mm cranks, but am a poor climber and if I could get a few percent of speed from different cranks I'd take it.
I made this comment and never really thought that seriously about trying it, but now that this thread has resurfaced it occurs to me that I now have an indoor smart bike that can swap between crank lengths in a minute and ride an exactly repeatable virtual course.

Hmm.
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Old 12-07-21, 11:48 AM
  #35  
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Originally Posted by antimonysarah View Post
I made this comment and never really thought that seriously about trying it, but now that this thread has resurfaced it occurs to me that I now have an indoor smart bike that can swap between crank lengths in a minute and ride an exactly repeatable virtual course.

Hmm.
Two years later, I'm still in favor! Just make sure you have the correct leg extension and let us know the results.
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Old 12-07-21, 11:57 AM
  #36  
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I would use the Shimano for a few reasons - the length isn't going to make much difference, Shimano chainrings shift much better than FSA chainrings IME, and they are a wee bit lighter (although I doubt this will make the least bit of difference).

You body needs to output power to keep your bike moving through the wind or up a hill, and the amount of power it takes to ride up a is the same if your legs are making a circle with a 165mm radius or a 170mm radius, and the power you can produce is pretty constant if you take the time to get used to minor differences.
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Old 12-07-21, 12:07 PM
  #37  
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I've ridden brevets with cranksets from 170mm to 200mm and am considering 150mm now. I think it is a pretty complicated subject to be honest. Sore hip flexors might be an indication cranks are too long.
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Old 12-08-21, 01:00 PM
  #38  
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I have had bad knees for the past half century. Often on longer rides I have to add a patellar band to limit knee pain part way through the ride. I have 170mm cranks on a vintage bike, have 175mm on the rest of my bikes. After I do a long ride, I find that walking up a set of stairs seems to be easier on my knees after riding my vintage bike with the shorter crank, but there could be other factors, this is not a scientific test. A 5mm crank arm difference is roughly a 3 percent difference in torque on the crank.

As noted above by several others, cadence would likely rise on shorter cranks and you might find that you are favoring a slightly lower gear since your torque on the crank is reduced slightly, if you are doing comparisons on a virtual training machine with adjustable crank arms, you might be able to measure these differences.
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Old 12-08-21, 01:17 PM
  #39  
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Originally Posted by Tourist in MSN View Post
I have had bad knees for the past half century. Often on longer rides I have to add a patellar band to limit knee pain part way through the ride. I have 170mm cranks on a vintage bike, have 175mm on the rest of my bikes. After I do a long ride, I find that walking up a set of stairs seems to be easier on my knees after riding my vintage bike with the shorter crank, but there could be other factors, this is not a scientific test. A 5mm crank arm difference is roughly a 3 percent difference in torque on the crank.
My girlfriend experiences the same thing- she finds she can walk better after riding. Age does things to us- stuff I could tolerate 40 years ago are out of the question not. But because I've paid attention to how bike fit really works (including crank length, foot position on the pedals and so on) I can ride further now on a more comfortable bike than I ever could when I was in my 20s. And I can ride faster now than 15 years ago...
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Old 12-08-21, 04:34 PM
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I find sensitivity in my knees with 2.5mm of difference. All my bikes have 170's now except for my BMX/cruiser stuff. 165's might be coming sooner than I would like.
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Old 12-08-21, 11:02 PM
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Originally Posted by canopus View Post
I find sensitivity in my knees with 2.5mm of difference. All my bikes have 170's now except for my BMX/cruiser stuff. 165's might be coming sooner than I would like.
No shame in shorter cranks! I put 165's on my fixed-gear not long after building it (I think from Sheldon Brown's influence) and after that worked so nicely, more of my bikes have gotten 165mm cranks when I decided on new ones.
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Old 12-10-21, 02:59 PM
  #42  
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I was the OP on this thread. Even though it's been a year, I think I went with a new set of 165s for build at the time, which was a 1986 Trek Elance 330, converted to 650b, One reason was for saving my knees just a little bit more, and second was to keep my pedals from hitting the pavement due to the smaller 650b tires.
Its been a good bike for the local brevets that have us on longer stretches of gravel and/or two track paths.
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Old 12-15-21, 01:26 PM
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Originally Posted by antimonysarah View Post
I made this comment and never really thought that seriously about trying it, but now that this thread has resurfaced it occurs to me that I now have an indoor smart bike that can swap between crank lengths in a minute and ride an exactly repeatable virtual course.

Hmm.
Try it! We need data!
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Old 12-15-21, 05:47 PM
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Originally Posted by canopus View Post
I find sensitivity in my knees with 2.5mm of difference.
I doubt it. 2.5mm probably just exceeds the manufacturing tolerance for all but the best of the best components. Your cranks are mismatched by that much right now and you don't even notice. And as long as I am here I will observe that the 2.94% loss of torque going to the shorter cranks is not easily compensated for by downshifting since few clusters have less than a 9% change between gears. It's even bigger at the extremes. Seems to me that headwinds and climbing are the places where one would be least likely to want shorter cranks.
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Old 12-15-21, 06:43 PM
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Originally Posted by Leisesturm View Post
I doubt it. 2.5mm probably just exceeds the manufacturing tolerance for all but the best of the best components. Your cranks are mismatched by that much right now and you don't even notice. And as long as I am here I will observe that the 2.94% loss of torque going to the shorter cranks is not easily compensated for by downshifting since few clusters have less than a 9% change between gears. It's even bigger at the extremes. Seems to me that headwinds and climbing are the places where one would be least likely to want shorter cranks.
Taguchi is rolling over in his grave.

I'd be shocked if Shimano cranks had 1/10 that variation.
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Old 12-15-21, 07:59 PM
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Originally Posted by Leisesturm View Post
I doubt it. 2.5mm probably just exceeds the manufacturing tolerance for all but the best of the best components. Your cranks are mismatched by that much right now and you don't even notice. And as long as I am here I will observe that the 2.94% loss of torque going to the shorter cranks is not easily compensated for by downshifting since few clusters have less than a 9% change between gears. It's even bigger at the extremes. Seems to me that headwinds and climbing are the places where one would be least likely to want shorter cranks.
If manufacturing tolerances were allowed to be 2.5mm out of spec, we would still be working with wood because nothing would fit together.
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Old 12-16-21, 07:04 AM
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I mentioned above (in post 38) that I have bad knees. And mentioned that after a long ride I find it is easier to walk up a flight of stairs if I rode my 170mm crankarm bike instead of one of my 175mm crankarm bikes. But for me the difference in crank arm length is quite small and hard to notice. But I have good knee flexibility and hip flexibility. I think if my range of motion was more limited, that is where I would be shopping for much shorter crank arms.

My knee problems are related to fragile anatomy. Occasionally if I push hard on my knees, I get a sudden shot of pain, which might go away in hours or in months. Thus, I have not stood on the pedals to accelerate when a light turns green for over a decade, never stand on the pedals anymore for power.

For me, low enough gears to make sure that I do not overstress knee joint is much more important than crank arm length.

I am not a medical professional, I am a retired engineer. I am looking at my knee issues the way that an engineer looks at a piece of machinery, bearing strength and articulation angles, etc. But I could certainly see how people with flexibility problems could benefit from shorter crankarms. But I think they should make sure that they have low enough gearing to compensate for their reduced torque on the crankset.
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Old 12-16-21, 02:02 PM
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Originally Posted by Leisesturm View Post
I doubt it. 2.5mm probably just exceeds the manufacturing tolerance for all but the best of the best components. Your cranks are mismatched by that much right now and you don't even notice. And as long as I am here I will observe that the 2.94% loss of torque going to the shorter cranks is not easily compensated for by downshifting since few clusters have less than a 9% change between gears. It's even bigger at the extremes. Seems to me that headwinds and climbing are the places where one would be least likely to want shorter cranks.
Even cranks 100 years old do not have that kind of variance. Ask me how I know.

The issue here is torque of course- and with longer cranks you have more torque. But since the issue is torque, how much torque can your knees handle before they cause you to stop riding? When you run shorter cranks, its easier to spin faster, so when confronted with a headwind or hill you might have to gear down a bit. I've gone from 175s to 170s and not found that I had to mess with the gearing on the bike. If you went to 155s its likely a different matter.
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Old 12-16-21, 04:00 PM
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Originally Posted by Salubrious View Post
Even cranks 100 years old do not have that kind of variance. Ask me how I know.

The issue here is torque of course- and with longer cranks you have more torque. But since the issue is torque, how much torque can your knees handle before they cause you to stop riding? When you run shorter cranks, its easier to spin faster, so when confronted with a headwind or hill you might have to gear down a bit. I've gone from 175s to 170s and not found that I had to mess with the gearing on the bike. If you went to 155s its likely a different matter.
I was being deliberately hyperbolic to make a point, and you just helped me.

I have five single bikes, four tandems and two recumbents. There is every length of crank on them from 165 through 175 and I couldn't tell you what has what. It is simply a non-issue, that small a change. Well, if it isn't costing anything, why not. But to remove a perfectly fine set of 170mm cranks. Pay ... what, $100? $150? More? You'd better, if you want something decent. Or find them used. Now, can you make the swap yourself or do you have to $$$ to have it done by the LBS? For 5mm? I don't think so. That is all I'm saying and all I ever will say about it. A 3% change just isn't worth three figures to try out.

We have a double recumbent tandem built for Dutch people. At 5'10" I can 'just' reach the pedals with the 170's that are in the Captains spot. At 5'6" my wife can 'just' reach her pedals. There isn't any way to fix that. Theoretically my wife should be alright but she would like some shorter cranks. The rule is "the Stoker is always right" so I am duty bound to make it right for her. I'm pretty sure her cranks are 170's just like mine. Taking my own medicine, I am not going to swap a full out tandem crankset. I will find some crank shorteners. Happiness begins at 155mm. Go big, or go home. YMMV.
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Old 12-16-21, 04:35 PM
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Originally Posted by Leisesturm View Post
...
We have a double recumbent tandem built for Dutch people. At 5'10" I can 'just' reach the pedals with the 170's that are in the Captains spot. At 5'6" my wife can 'just' reach her pedals. There isn't any way to fix that. Theoretically my wife should be alright but she would like some shorter cranks. The rule is "the Stoker is always right" so I am duty bound to make it right for her. I'm pretty sure her cranks are 170's just like mine. Taking my own medicine, I am not going to swap a full out tandem crankset. I will find some crank shorteners. Happiness begins at 155mm. Go big, or go home. YMMV.
Several years ago I saw these when I was doing a search on their site for something, thought that these were really weird. Reading your post, I thought you might be interested, but they apparently only fit square taper.
https://www.sjscycles.co.uk/componen...nk-shorteners/

Now the bad news, since Covid, their shipping fees have been a bit high.

If you are interested, you probably should e-mail them first with your brand and model of cranks so they can tell you if they should fit or not.
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