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  #1  
Old 10-10-2020, 01:41 PM
ridethecliche ridethecliche is offline
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Fit indications for shorter cranks

I just wanted to start a bit of a discussion on the topic of using shorter cranks to solve fit issues. Under what circumstances is the rec for moving to shorter cranks more than just personal preference?

One of the reasons that I'm asking is that an issue I've always encountered has been my knees whacking my stomach in the drops. I've adjusted saddle tilt slightly in the past and have to do it a bit again to adjust my hip angle but that's besides the point. My bike currently is a bit on the smaller side for me (running a 130 stem) but I have very little bar drop at about 6cm to the tops.

In any event, hoping for a more general discussion. The other threads I've seen on the topic deal more with the availability.
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Old 10-10-2020, 02:29 PM
giordana93 giordana93 is offline
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definitely one of the reasons tri guys are going to shorter cranks is to get the torso lower without bumping into knees so it's definitely a thing. also easier on the knees generally because you're forced to spin more
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Old 10-10-2020, 03:21 PM
ridethecliche ridethecliche is offline
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Originally Posted by giordana93 View Post
definitely one of the reasons tri guys are going to shorter cranks is to get the torso lower without bumping into knees so it's definitely a thing. also easier on the knees generally because you're forced to spin more
Yeah I've had some knee issues in the past but I'm on 172.5s.

The knee hitting torso thing isn't really weight related for me. I have had back surgery so my flexibility is all sorts of weird but I've been trying to do a couple of yoga sessions during the week to help with that.

Also curious if it will actually hurt my sprint numbers. Moving my cleats back a bit didn't have the deleterious effect I expected it to.
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Old 10-10-2020, 05:14 PM
Peter P. Peter P. is offline
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I don't feel crank length should be adjusted to solve the knees hitting the torso issue you are having.

Crank length should be adjusted to leg length and personal pedaling style.

I don't know what size frame you ride, your seat height, or crank length. A picture of the bike would be interesting to see, particularly with that 13cm stem.

From the limited information you supplied, I think your position is unorthodox and I'll admit I haven't seen your position, and to cure the interference problem, I'd just raise the stem.
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  #5  
Old 10-10-2020, 07:56 PM
ridethecliche ridethecliche is offline
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This is an older picture. Since then I got a fit and saddle came down and forward a cm.

http://imgur.com/a/ViE0cW8

Frame is a medium (fitter said it measured close to a 56tt). I'm 5'10.
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  #6  
Old 10-11-2020, 07:52 AM
chow834 chow834 is offline
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Personally went from 165mm cranks down to 155mm (following the recommendation of a bike fitter), and will be sticking to 155s.

1. Allows for a position with more pelvic tilt - lower, more stable, and more aero (if it matters)

2. Supposedly less stress on the leg muscles/joints over longer distances as you move them through a smaller range of motion (though this might only apply if the original crank length was way too long for you)

Generally I would think downsizing cranks isn't usually a problem as tall track riders typically use 165mm cranks on the velodrome - and hence don't think sprint numbers will be affected
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  #7  
Old 10-11-2020, 01:02 PM
ridethecliche ridethecliche is offline
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Quote:
Originally Posted by chow834 View Post
Personally went from 165mm cranks down to 155mm (following the recommendation of a bike fitter), and will be sticking to 155s.

1. Allows for a position with more pelvic tilt - lower, more stable, and more aero (if it matters)

2. Supposedly less stress on the leg muscles/joints over longer distances as you move them through a smaller range of motion (though this might only apply if the original crank length was way too long for you)

Generally I would think downsizing cranks isn't usually a problem as tall track riders typically use 165mm cranks on the velodrome - and hence don't think sprint numbers will be affected
That's interesting, just read a bunch more about this as it seems that the shorter crankarms could also help with some knee issues that I've had in the past. I read some stuff here: https://lermagazine.com/article/at-a...e-and-hip-pain

I may grab a set to try out over the winter. I've been working with a fitter and I'll see what he says, but I think I'm still keen on trying it. Unfortunately I have 2 left sided PMs that are for 172.5 cranks, but I guess it's easy enough to sell and rebuy. Better than not riding due to pain and other issues!
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Old 10-11-2020, 04:38 PM
Peter P. Peter P. is offline
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Quote:
Originally Posted by ridethecliche View Post
This is an older picture.
Thanks for the photo. It helps give some perspective.

The setup seems just fine for a "normal" riding position. The saddle to bar drop is reasonable, and you've wisely got the max number of spacers under the stem. The stem length doesn't look out of proportion with the frame or your setup. Even your crank length as mentioned sounds reasonable.

But when you mention your back issues, I start to think you have to raise your stem. If inverting the stem will gain some height, try that first. Next would be buying a cheapo stem on eBay that has more rise. If you find a stem that cures your problem, THEN you can spend the money on something fancier.

Other than that, I don't see a solution other than buying a frame with more stack height. I don't feel all the stretching and yoga is going to stop your knees from hitting your torso.
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  #9  
Old 10-11-2020, 06:57 PM
ridethecliche ridethecliche is offline
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Quote:
Originally Posted by Peter P. View Post
Thanks for the photo. It helps give some perspective.

The setup seems just fine for a "normal" riding position. The saddle to bar drop is reasonable, and you've wisely got the max number of spacers under the stem. The stem length doesn't look out of proportion with the frame or your setup. Even your crank length as mentioned sounds reasonable.

But when you mention your back issues, I start to think you have to raise your stem. If inverting the stem will gain some height, try that first. Next would be buying a cheapo stem on eBay that has more rise. If you find a stem that cures your problem, THEN you can spend the money on something fancier.

Other than that, I don't see a solution other than buying a frame with more stack height. I don't feel all the stretching and yoga is going to stop your knees from hitting your torso.
I've had back surgery twice but my back hasn't really been bothering me much with this setup. Even when i raced back in the day, I rarely rode in the drops because of the contact and my seat height and bar drop was way more aggressive.

I'm actually thinking of picking up some 165mm cranks to trial and see how they feel. I quit riding due to knee issues 12 years ago and I feel them starting to creep back in. Only bothers me riding and I just got a fit so I'm hoping it's not that.

Frankly I'd ride 150's if it meant riding pain free lol!
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  #10  
Old 10-12-2020, 01:15 AM
chow834 chow834 is offline
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Quote:
Originally Posted by ridethecliche View Post
That's interesting, just read a bunch more about this as it seems that the shorter crankarms could also help with some knee issues that I've had in the past. I read some stuff here: https://lermagazine.com/article/at-a...e-and-hip-pain

I may grab a set to try out over the winter. I've been working with a fitter and I'll see what he says, but I think I'm still keen on trying it. Unfortunately I have 2 left sided PMs that are for 172.5 cranks, but I guess it's easy enough to sell and rebuy. Better than not riding due to pain and other issues!
Good read! I’ve seen 165mm stages PMs, and manufacturers seem to be jumping on the shorter cranks trend with current gen Shimano going down to 160mm
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  #11  
Old 10-12-2020, 03:54 PM
ridethecliche ridethecliche is offline
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Quote:
Originally Posted by chow834 View Post
Good read! I’ve seen 165mm stages PMs, and manufacturers seem to be jumping on the shorter cranks trend with current gen Shimano going down to 160mm
Rotor makes them down to 150 I believe.

I guess I'm desperate enough to try going down a bunch at this point. I quit riding because of this issue. Just trying to find a solution.
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  #12  
Old 10-12-2020, 11:14 PM
giordana93 giordana93 is offline
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Quote:
Originally Posted by ridethecliche View Post
Rotor makes them down to 150 I believe.

I guess I'm desperate enough to try going down a bunch at this point. I quit riding because of this issue. Just trying to find a solution.
desperate? I'm a little confused. In OP you seemed to complain about knees interference with stomach and not something too serious. I would caution against 1) changing too many things at once--you just got a fit, what did that involve? 2) going too extreme--take an aspirin, not the whole bottle (credit to Harvey Penick). I'll note that in the article riders a,b,c, & d were short, between 4' 10" and 5' 6". If you're taller than 5' 2" I wouldn't go shorter than 165. And the fact that your legs are long enough to hit you probably means you are more leg than torso. Anyway. just my .02
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  #13  
Old 10-13-2020, 12:56 AM
ridethecliche ridethecliche is offline
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Quote:
Originally Posted by giordana93 View Post
desperate? I'm a little confused. In OP you seemed to complain about knees interference with stomach and not something too serious. I would caution against 1) changing too many things at once--you just got a fit, what did that involve? 2) going too extreme--take an aspirin, not the whole bottle (credit to Harvey Penick). I'll note that in the article riders a,b,c, & d were short, between 4' 10" and 5' 6". If you're taller than 5' 2" I wouldn't go shorter than 165. And the fact that your legs are long enough to hit you probably means you are more leg than torso. Anyway. just my .02
Appreciate the input.

I bought the cranks on a whim. I'm still making changes with the fitter but if all else fails I guess this will be something that will be tried out as well. Long and short of it is that the saddle came down and forward. My cleats were more or less set up right, though I've made some micro adjustments to that. I have a pretty collapsed arch on my right foot so have some arch support and shims so the system doesn't collapse inward on the downstroke, but I have a bit of a wobble at the top of the stroke that has been a bit hard to dial out. This increase in knee pain just ended up popping up as an issue after I started this thread, though it's an old issue that only pops up on the bike.

The knee interference issues makes it difficult to use the drops, which is semi-serious in faster scenarios and for more control when riding.
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  #14  
Old 10-13-2020, 01:30 AM
l0n3rider l0n3rider is offline
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if i understand it correctly .. assuming your saddle height and for-aft are setup within acceptable range ..

the crank length is more about range of motion. to test this .. ride your bike on a trainer .. pedal in single leg ..

the crank length will reveal your range of motion at the top stroke .. if you do not have the range of motion .. there will be "clunking" sound .. and normally your knee will move side way at the top of the stroke. it will give knee problem in the future (if not now)

try it in various hand positions .. at the bar, at the hood, in the drop ..

shorter crank length will give more space .. easier for your hip flexor .. and this relates to your hand position as well .. in the drops, your abdomen is lower and less space between your thigh and your abdomen at the top of the stroke

how should you setup? it depends .. if you rarely pedal while your are in the drops .. then slightly out of range is OK .. but make sure when your hands are at the bar and at the hoods .. your pedal is smooth and your knee can move straight without have to go side way at the top of the stroke .. no "clunking" sound ..

you can shorter your crank or work on your hip flexor ..

my less than 2 cents

Last edited by l0n3rider; 10-13-2020 at 01:33 AM.
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  #15  
Old 10-13-2020, 07:00 PM
ridethecliche ridethecliche is offline
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Quote:
Originally Posted by l0n3rider View Post
if i understand it correctly .. assuming your saddle height and for-aft are setup within acceptable range ..

the crank length is more about range of motion. to test this .. ride your bike on a trainer .. pedal in single leg ..

the crank length will reveal your range of motion at the top stroke .. if you do not have the range of motion .. there will be "clunking" sound .. and normally your knee will move side way at the top of the stroke. it will give knee problem in the future (if not now)

try it in various hand positions .. at the bar, at the hood, in the drop ..

shorter crank length will give more space .. easier for your hip flexor .. and this relates to your hand position as well .. in the drops, your abdomen is lower and less space between your thigh and your abdomen at the top of the stroke

how should you setup? it depends .. if you rarely pedal while your are in the drops .. then slightly out of range is OK .. but make sure when your hands are at the bar and at the hoods .. your pedal is smooth and your knee can move straight without have to go side way at the top of the stroke .. no "clunking" sound ..

you can shorter your crank or work on your hip flexor ..

my less than 2 cents
This is fair but sometimes life, previous injury, and biomechanics are hard to alter even with good stretching. I could arguably stretch more (and should) but have been doing a decent amount of yoga to help with this.

The cranks are a last case resort of sorts. Still working with the fitter and likely going to see a sports med doc for a referral to a good PT.

If shorter cranks help negate the issue while I work on keeping things limber and let me keep riding without making things worse or losing power etc... why not go for it!?

But you're right. My knee has a slight wobble in it at the top of the stroke. I bet that's exacerbating things because the tracking goes off when that happens. I've done things like run and snowboard with no issue so I don't think there's anything structurally wrong with my knee. Will try to follow up with doc/PT and even look into a fitting with a PT fitter if I can't figure this out...
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