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Shorter Cranks for Climbing

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Shorter Cranks for Climbing

Old 10-27-21, 06:16 AM
  #76  
AnthonyG
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Originally Posted by cubewheels View Post
Here in the Philippines, if you could increase the salary of your outsourced jobs here, maybe we can afford more expensive brands that carries our size or even give us the courage to burn cash on bike fitting The cheap Chinese brands we can actually afford (the equivalent of Walmart bikes in USA) have limited sizing options.

The price of Trek bikes for example is actually more expensive here, in a country that is supposed to be poor. Same goes for medicines. It's a cruel world we live in. Consider youselves lucky if you have time to care about those things like bike fit.
Trek bikes are not sized better than any other brand of bike. In fact the cheap Chinese bikes you get are most likely sized better than the Trek's.
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Old 10-27-21, 04:51 PM
  #77  
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Originally Posted by cubewheels View Post
Yes, they have better sizes in the >$600 price but most cannot afford the price.
Most here buy the 200 to $300 stocks and they quickly run out of stock and good sizes first.
Yeah NO.

Trek bikes are fundamentally the wrong size for an average person of Asian descent. It's not just a matter of buying a small or an extra small. Treks are just fundamentally built for quite tall people and no amount of fiddling will make them right for someone 5'5" or less.
Now I don't really have any experience with the Chinese brands that you are referring to, yet none of them could be worse than Trek's are and some of them would be better.
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Old 11-02-21, 03:03 AM
  #78  
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I'd just like to point out a few things:

- once you adjust your crank length, you should no longer merely be discussing cadence. You should also be discussing foot speed. If you went from a 170mm crank to a 160mm crank and your cadence only increased by ~6%, your effective foot speed is the same and you have seen no gain. In fact, you're now at a detriment because you have to fire your legs at a higher rpm, which requires more focus, more overhead etc. That being said, I think people who move to shorter cranks find that their rpms increase more than the "break even" amount due to the limited knee flexion.

- One reason why you may see less knee pain when switching to a shorter crank is that, if your knee has any wobble (even a couple mm), a shorter vertical ROM will also reduce lateral displacement. Preventing your knee from bending or straightening too much will allow you to more easily compensate for poor cleat alignment. This does not mean you "need" shorter cranks.

- shorter cranks allow you to sit farther back relative to the pedals while still achieving the same minimum hip angle. This can improve muscle engagement and reduce the amount of weight on your hands.

- All bike fit is a compromise. More specifically, it involves optimizing for the intended use. If you're going to be climbing steep hills out of the saddle frequently, you should probably go for longer cranks. Most people have a natural rhythm (60-80rpm) that they like when swaying the bike and it's going to be hard to increase that, as is necessary if you reduce crank length.

- If you're doing flatter rides, shorter cranks are almost always faster because they will almost always allow you to get more aero and rarely will it compromise your power.

- crank length optimization follows a hockey stick curve for most people. Too short is slower, as is too long. But going *slightly* too long can be disastrous whereas going significantly too short will only be a slight detriment. When in doubt, go shorter.
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Old 11-03-21, 07:29 PM
  #79  
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Originally Posted by smashndash View Post
I'd just like to point out a few things:

- once you adjust your crank length, you should no longer merely be discussing cadence. You should also be discussing foot speed. If you went from a 170mm crank to a 160mm crank and your cadence only increased by ~6%, your effective foot speed is the same and you have seen no gain. In fact, you're now at a detriment because you have to fire your legs at a higher rpm, which requires more focus, more overhead etc. That being said, I think people who move to shorter cranks find that their rpms increase more than the "break even" amount due to the limited knee flexion.

- One reason why you may see less knee pain when switching to a shorter crank is that, if your knee has any wobble (even a couple mm), a shorter vertical ROM will also reduce lateral displacement. Preventing your knee from bending or straightening too much will allow you to more easily compensate for poor cleat alignment. This does not mean you "need" shorter cranks.

- shorter cranks allow you to sit farther back relative to the pedals while still achieving the same minimum hip angle. This can improve muscle engagement and reduce the amount of weight on your hands.

- All bike fit is a compromise. More specifically, it involves optimizing for the intended use. If you're going to be climbing steep hills out of the saddle frequently, you should probably go for longer cranks. Most people have a natural rhythm (60-80rpm) that they like when swaying the bike and it's going to be hard to increase that, as is necessary if you reduce crank length.

- If you're doing flatter rides, shorter cranks are almost always faster because they will almost always allow you to get more aero and rarely will it compromise your power.

- crank length optimization follows a hockey stick curve for most people. Too short is slower, as is too long. But going *slightly* too long can be disastrous whereas going significantly too short will only be a slight detriment. When in doubt, go shorter.
Good points. But why move back with shorter cranks? When my stoker went from 170 to 151mm cranks, I tried doing a KOPS but her power dropped off. I moved her saddle back to where it was and that seems to work better for her.

We have several bikes with crank lengths all over the place. They all work fine - one simply has to do what one has to do to move the bike, i.e. put down the same power. It doesn't take long to figure out what one has to do, even without a PM. I just now took it into my head to go around and see where the aft pedal spindle is w/r to sit bone location on the saddle on our bikes. It's all over the place too. The bikes have differing seat tube angles, different seat post setbacks, different saddles, and the idea of having the seatpost clamp not out at either end of the rails is also in play. And like I say, they all ride fine, i.e. exact BB placement doesn't seem a huge deal unless it's way off as in the case of moving her saddle all the way to the end of the rails with a CoblGoblr post which has a 30mm setback.

We know that KOPS is not the way to go, and I'm thinking that the rider CG w/r to BB might be a better way to think about it. Balance while pedaling seems most important to me. That'll vary somewhat with crank length, but in general, we don't push down all that hard, so it shouldn't vary by much. Another argument for going by BB location is that we push forward quite a bit at the top of the pedal stroke and pull back at the bottom, so the physical mechanics of that are also in play.

I'm thinking I need to develop some intelligent way to determine where both pedals and the BB should be w/r to sit bone location and set all our bikes up the same way. We have about the same hip angle on all of them.
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Old 11-03-21, 07:52 PM
  #80  
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Originally Posted by Carbonfiberboy View Post
Good points. But why move back with shorter cranks? When my stoker went from 170 to 151mm cranks, I tried doing a KOPS but her power dropped off. I moved her saddle back to where it was and that seems to work better for her.

I'm thinking I need to develop some intelligent way to determine where both pedals and the BB should be w/r to sit bone location and set all our bikes up the same way. We have about the same hip angle on all of them.
So I'm personally in favor of forward fits. Mine is quite forward, but I also am somewhat strong (4W/kg) and race. Some people like rearward fits and have no issue putting down huge power from that position. I think it comes down to preference, cadence, body weight, upper body/core strength, fitness, and what kinds of rides the person is doing (crits vs climbing vs group rides vs touring). Generally, the higher the average pedal force per kilo of body weight, the more optimal a forward fit is. You need to be able to counterweight your pedal force without falling forward too much on your hands.

I honestly don't know if there's a reliable way to nail fore-aft (relative to the pedal at the forward position) given how variable the optimal position is. But I think Steve Hogg has a method to get within a reasonable ballpark for most people. And from there it's just about tweaking. If the rider is consistently sliding forward or bobbing or jumping out of the saddle, they might need a slightly more forward position. Too far forward is more obvious: Quad overengagement and numb hands.

That being said, I think saddle fore-aft is a power/aero optimization problem. If moving the CoG relative to the pedals within a reasonable range causes pain to appear or disappear, that's a red flag.

Last edited by smashndash; 11-03-21 at 07:56 PM.
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Old 01-26-22, 08:06 AM
  #81  
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Don't over think it

I'm 6'3" and have been riding 150 and 152mm cranks on all my bikes, road and mountain, for several years. I did it for knee pain, which it solved, not for any performance reasons.

I did do a lot of research before jumping in, though, and came to the conclusion that there are too many variables to predict what will happen on a particular bike. For instance, the knee-pedal relationship changes, but depends a lot on geometry. But you might not be able to push the saddle back enough to prevent a knees forward of the pedals a la triathlon bikes.

Also, remember that there are a lot of theories about how crank length will change metric x, but the bike is a machine almost purpose built to compensate for changes in leverage. So your real world experience will vary!

My advice is try it. It is not a big investment. I can't speak to US availability and pricing, but Suntour sells the XCT Jr crank at 152mm, and i use this converted to a 1x on my mountain bike. They cost 25 Euro, don't look great, but work fine. Stronglight sells a rebranded and shortened Sugino XD2 called the Impact Kid in a bunch of different lengths for about 50 Euro. These are both shortened versions of adult cranks, so plenty strong, and exactly what you would get using a crank shortening service.

If you like ithe result but want something fancier, the TA Carmina is not so expensive, so far as cranks go these days.
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Old 01-26-22, 08:17 AM
  #82  
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Originally Posted by Leisesturm View Post
The thread bump gave me the (sad) opportunity to read this missed thread in its entirety. Holy Moly what a cluster____ of speculation, misinformation, misperception and all manner of illogic. Carbonfiberboy is about the only poster making consistent sense. I'm sure he isn't the only one, but cripes. Listen. the percent change in ANYTHING between 170 and 175 is less than 3%! 2.94 if we want to get exact about it. Not perceptible. When you are talking about as gross an anatomical usage as an 80rpm cadence ... 3% gets quickly lost in the white noise of lactic acid overload. I don't doubt that for the first few tentative strokes with the new setup a person might think they have made a significant change, but once they start hammering it all just goes away. It really does.

A 10% change ... now you're talking. Why anyone would want 10% LESS torque to work with, I don't know, but if you are going to make changes, 10% is about the minimum that actually makes any real difference. For a 175mm crank that would be a 160mm crank. If you are doing it right you will also lower your gears 10%. Practically speaking you wouldn't try to lower each and every cog and chainring, just at the ends. Or you could drop down a gear (~13%) whenever you think about it. Chances are you'll do that automatically when you start to fatigue from having 10% less torque to work with.

As I have said before, the cranks we have are a compromise. Ideally they would be longer! All human powered endeavor is a need for speed. Our bicycles are descended from UCI sanctioned racing steeds that sought to allow constant high cadence pedaling for as long as possible. This meant keeping cadence constant through left and right hand turns at high speed. Much longer than 170mm and there is a real possibility of pedal strike in a corner and ... nobody wants that. Hybrids can run 175 because they run slower in the corners. But you are unlikely to see much below 160 or much more than 175 in regular production. Mainly because it makes little sense to have shorter cranks and 170/5 is the practical upper limit for longer ones without a frame redesign. Simplistic but true.

So why are there 155 ... 140. 100! Cranks? Because people want them. Misguided people, but they are a market. Fair game. Don't be that cyclist. Hold on to your money for something better than a crankset you don't need. The recumbent market is especially susceptible to the short crank thing. For 99% of recumbents standard cranks are just fine. The exceptions are those that enclose the riders feet as many only provide minimal clearance around the pedal circle. American feet just don't fit inside the toe boxes of European velomobiles with sporting pretensions. Sometimes cranks as short as 130mm need to be used but when you have the kind of drag coefficient the average velomobile does, what are a few (dozen) newton-meters of torque lost?

Look. I'm all for people doing what makes them happy. I just am dismayed that the reboot of this thread is just carrying the same old misinformation forward. At least know why you are doing something. Longer cranks are not the devil. Shorter cranks do not make you faster, or give you more endurance. At least not in the way most of you use them! Shorter cranks do not even really help your knees. Lower gears are a much better way of saving your knees than trying to limit the effective range of your knee flexion. TL;DR: unless you have a real good reason, and that is unlikely, the crankset sold with your bike, at least with respect to length, probably suffices. Piffling changes of 2.5mm and 5mm are just a colossal waste of time and money. Unless you are buying cheap crap cranksets and why would you do that?

I've yet to meet the production bike that wasn't grossly overgeared out of the box. If you are still using the 30/42/52 triple that came with your hybrid, or the 50/39 that came with your road racer you are not having a quality experience. The 30 (front) x 32 (rear) combination commonly found on most hybrids as the "granny" gear is about 27" which is also about the "gear'" that humans walk in. The low gear on my bike is 22 x 36. About 18". I don't expect a road racer to have an 18" low gear but if you guessed that the 39 (front) x 27(rear) low gear on many road bikes is too high, you'd be right. And you need LONGER cranks to wrestle that smb into submission, NOT shorter.
You have no idea what you are talking about.

You do realize the recumbent hour record was set on 130 mm cranks.

I've ridden 200 mm and also very short cranks. There are enormous benefits to short cranks in some applications.....better aerodynamics, easier to bring the pedal over the top (hip flexor issues), and lower inertial power losses from those big fat legs. Torque is a red herring, just use a smaller gear.

Instead of a lot of useless words, how about quoting some studies.
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Old 01-26-22, 09:02 AM
  #83  
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This thread needs a stake through the heart.
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Old 01-26-22, 11:41 AM
  #84  
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Originally Posted by GhostRider62 View Post
You have no idea what you are talking about.

You do realize the recumbent hour record was set on 130 mm cranks.

I've ridden 200 mm and also very short cranks. There are enormous benefits to short cranks in some applications.....better aerodynamics, easier to bring the pedal over the top (hip flexor issues), and lower inertial power losses from those big fat legs. Torque is a red herring, just use a smaller gear.

Instead of a lot of useless words, how about quoting some studies.
Is this a thread about recumbents? Is climbing a part of riding where one might benefit from lower torque? Instead of looking through my post history to pick fights how about you get over the fact that you don't like my style and that that is on you. I notice that that post of mine that so ticked you off another poster said pretty much the same thing I did. Why isn't theirs also 'lousy'? I stand by my opinions. Studies ... you say you've used 200mm cranks. What study could I find that would trump that?
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Old 01-26-22, 12:26 PM
  #85  
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I'm running 165mm cranks on my gravel bike and 175mm on my road bike. I like them both for different reasons. On my gravel bike, I have lower gearing and the shorter cranks help reduce toe strike on technical terrain. Also since I ride that bike on rougher terrain, out of saddle riding isn't an option for traction reasons. On my road bike, the 175mm cranks are awesome for torquing on road climbs and even my flat sprints benefit from the torque. I'm almost tempted to pick up a set of Dura-Ace 180mm cranks for that additional 5mm!

On a side note jumping back and forth between crank sizes, has showed me how to optimize my pedaling techniques and it's not all about crank length. For example I move forward on my saddle when I plan to spin at high cadence, which then utilizes a different set of muscles for spinning. When I go for seated sprints, moving back on my saddle utilizes another set of muscles to lay down the pedal power, while adjusting my hand positions on the drop bars. The great thing is that I can apply the same techniques to both crank sizes. Also when not cycling, I have a better idea on what leg/upper body muscles to work on when I'm doing strength training.
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Old 01-29-22, 12:52 PM
  #86  
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For me crank length is really about matching your personal range of joint motion. Go too long and you get problems with knee/hip angles etc. Go too short and you give away potential torque/leverage. But gearing is way more important for the latter, so I don't worry about that at all. I've recently moved from 175 to 172.5 on my road bike (simply because that's what my new bike came with). Can't say I've noticed any significant difference to be honest. But I'm 6'1" with relatively long legs, so 175 cranks are fine for me. All my mtbs have been on 175 cranks.
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Old 01-30-22, 04:37 AM
  #87  
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Originally Posted by PeteHski View Post
Go too short and you give away potential torque/leverage. But gearing is way more important for the latter, so I don't worry about that at all.
I Second the gearing point. This could be mechanically compensated (new cassette and chainrings) or through unconsciously hanging out in different grars more. Also, slightly changing riding position can have a significant impact.

Crank length is but one lever in a system with lots of variable levers. It would be a lot easier to make generalization if we were riding penny farthings with the cranks directly attached to the wheel, and no real flexibility in riding position. Then, I could understand heated debates about categorical statements of the performance impact of going from 175 to 165 or even 150.

I think we are used to everything on a bike being adjustable--stem length and angle, saddle height, etc etc--except crank lengths. Changing crank length seems like a huge deal because we are used to thinking it's a given and a constant. But 175 is just as arbitrary as any other length i think. I mean, i would seriously doubt if all the component makers independently settled on 175 after having done exhaustive independent research which showed conclusively how much better it was than 176 or 174. More plausibly, someone at Shimano just chose it, corporate decided it made fiscal sense to phase out tooling for other lengths, and then other companies followed them like sheep. Consumers bought what was sold.

But imaging Shimano had settled on 156 for whatever reason. Then bikes, including gearing and angle and bb drop would be designed around that number (don't estimate how much the CPSC hates pedal strike!). And then 156 would start to seem really obvious and meaningful.

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Old 01-30-22, 05:58 AM
  #88  
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Originally Posted by Frkl View Post
I Second the gearing point. This could be mechanically compensated (new cassette and chainrings) or through unconsciously hanging out in different grars more. Also, slightly changing riding position can have a significant impact.

Crank length is but one lever in a system with lots of variable levers. It would be a lot easier to make generalization if we were riding penny farthings with the cranks directly attached to the wheel, and no real flexibility in riding position. Then, I could understand heated debates about categorical statements of the performance impact of going from 175 to 165 or even 150.

I think we are used to everything on a bike being adjustable--stem length and angle, saddle height, etc etc--except crank lengths. Changing crank length seems like a huge deal because we are used to thinking it's a given and a constant. But 175 is just as arbitrary as any other length i think. I mean, i would seriously doubt if all the component makers independently settled on 175 after having done exhaustive independent research which showed conclusively how much better it was than 176 or 174. More plausibly, someone at Shimano just chose it, corporate decided it made fiscal sense to phase out tooling for other lengths, and then other companies followed them like sheep. Consumers bought what was sold.

But imaging Shimano had settled on 156 for whatever reason. Then bikes, including gearing and angle and bb drop would be designed around that number (don't estimate how much the CPSC hates pedal strike!). And then 156 would start to seem really obvious and meaningful.
I agree, the industry pretty much ignores all the studies regarding crank length vs leg length and flexibility. I like the attached summary below from a well regarded UK fitter and another very experienced fitter I discussed it with is of much the same opinion i.e. if in doubt go shorter, especially for endurance. I'm fortunate enough that my leg length fits into the narrow zone where 172.5 and 175 mm cranks happen to be a good match, but I would have no issues running 170 or even165 mm cranks. Given a free choice on a custom build I would probably go with 170 mm cranks, but bikes in my size invariably come with 175 or 172.5 cranks.

https://bikedynamics.co.uk/FitGuidecranks.htm
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Old 01-30-22, 07:20 AM
  #89  
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Originally Posted by cubewheels View Post
Huge impact depending on the riding condition.

A long 10% gradient climb for example is like riding with the saddle tilted 6 degrees more upward and with 6 degrees less seat tube angle (or few dozen millimeters of added set back). If your bike fit is optimal, you'll experience discomfort on a long 10% gradient climb. You'll find yourself pulling the handle bar and that will add to the effort of climbing.

A rather simple solution when you're coming up on a very long 10% gradient climb for example is stop at the beginning of the climb, adjust the saddle, add 6 degrees tilt downward and move the saddle forward around 20 to 30 millimeters. Climbing will feel significantly easier if you make such adjustments.

Of course when you reach the top of the climb or the hardest part is over, you should can then stop and restore your previous adjustments to the saddle.

One clever solution is use TT saddle like the ISM ones. You can sit on the nose of those saddles and the nose part is an optimal position for climbing (tilted down and positioned forward). You don't have to stop at the side of the road and make adjustments before a long climb.
I've always wondered about this. When you ride up a hill all the contact points remain in exactly the same relative orientation. So if you remain seated then your bike fit geometry does not change in the slightest. The only thing that actually changes is the direction in which gravity acts on your centre of mass i.e. there is a larger component of gravity pushing you rearward on the bike vs vertically downward. Obviously that in itself is a significant change, but I'm not sure it warrants a major change in saddle position. Especially not of the magnitude described above.

Anyway this winter I have had the benefit of training on a Wahoo Kickr Bike, which can tilt to simulate anything up to 20% gradients. Having experimented with both saddle fore-aft and saddle tilt I've come to the conclusion that it isn't worth changing either of them. Although I have to say my particular saddle (Fizik Argo Tempo) has a very pronounced tail kick-up starting from the middle of the saddle, which acts as an automatic back-stop when climbing. If I had a more traditional flat saddle I probably would tilt it downward for extensive climbing. But I wouldn't necessarily move the saddle forward unless the climb was so steep that I was struggling to stay centred on the bike - in which case I would be standing anyway.

What I have noticed is that I actually prefer my default bike fit when climbing moderate gradients in the 5-7% range. That's about the point where my hands are pretty much unweighted on the bars. On the flat I feel a little more pressure on my hands in the name of compromise between comfort and bar height.

Last edited by PeteHski; 01-30-22 at 07:28 AM.
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Old 01-30-22, 12:13 PM
  #90  
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Originally Posted by PeteHski View Post
I've always wondered about this. When you ride up a hill all the contact points remain in exactly the same relative orientation. So if you remain seated then your bike fit geometry does not change in the slightest. The only thing that actually changes is the direction in which gravity acts on your centre of mass i.e. there is a larger component of gravity pushing you rearward on the bike vs vertically downward. Obviously that in itself is a significant change, but I'm not sure it warrants a major change in saddle position. Especially not of the magnitude described above.

Anyway this winter I have had the benefit of training on a Wahoo Kickr Bike, which can tilt to simulate anything up to 20% gradients. Having experimented with both saddle fore-aft and saddle tilt I've come to the conclusion that it isn't worth changing either of them. Although I have to say my particular saddle (Fizik Argo Tempo) has a very pronounced tail kick-up starting from the middle of the saddle, which acts as an automatic back-stop when climbing. If I had a more traditional flat saddle I probably would tilt it downward for extensive climbing. But I wouldn't necessarily move the saddle forward unless the climb was so steep that I was struggling to stay centred on the bike - in which case I would be standing anyway.

What I have noticed is that I actually prefer my default bike fit when climbing moderate gradients in the 5-7% range. That's about the point where my hands are pretty much unweighted on the bars. On the flat I feel a little more pressure on my hands in the name of compromise between comfort and bar height.
I've also noticed that my hands are way more comfortable on up hills and undulating terrain for that exact reason

I also have disproportionately short legs and a heavy muscular torso which is **** for cycling and hand comfort 😂
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Old 01-30-22, 07:11 PM
  #91  
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I find shorter cranks better for higher cadence and tucked positions that allow knees to sit lower for a more comfortable tuck - just remember, every 1cm you shorten your crank, you should raise your seat by 1cm, which will actually give you 2cm of knee clearance to your body.

For lower cadence, especially where you don't tuck I'm more likely to stick with a slightly longer crank.
I'm 5'7", and I like a 170 on drop bar bikes and a 175 on flat bar bikes, especially mtb.
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Old 01-31-22, 12:54 AM
  #92  
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After reading this thread, I ordered a 165mm crankset. It will be interesting to compare it to my 172.5mm one that is otherwise identical.

One thing has me a bit worried: Presumably I will need to raise the seat-post by 7.5 mm. The bike was custom-build around my sizing and presumably with the 172.5mm crankset in mind. I wonder if the bike will handle any differently. Presumably the saddle to bar drop will be the most significant change.

This experiment is primarily motivated by pedal strikes off-road with my 650b wheels (which also presumably alter the original intended geometry of the framebuilder).

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Old 01-31-22, 03:05 AM
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Originally Posted by SquishyBiker View Post
just remember, every 1cm you shorten your crank, you should raise your seat by 1cm.
I originally thought this too, but it's not a 1 to 1 relationship and shortening the crank does not necessarily or usually mean raising the saddle byll the same amount. Moving the saddle up also moves it back because the relevant measurement and point of reference is not directly down the seat tube with the crank aligned with it, but rather from contact point with the saddle (often but not always behind the seat post) to the pedal at the lowest part of the stroke (crank vertically down). So some of the difference is made up with horizontal movement of the saddle.

Hence the super scientistic slightly bent knee standard for seat post hight. This is to the lowest point of the pedal cycle.

The shallower the seat tube angle, the less up will be required to compensate for shorter cranks.

This also means that one could theoretically handle the entire change only by moving the saddle back, provided you have enough rails on your saddle. As a thought experiment, This can theoretically go on forever, and as you increase setback more and more, you must continually lower the saddle height. Eventually you end up with a recumbant, where (basically, this is a thought experiment), the entire saddle/pedal distance is accomplished through 100% horizontal setback and 0% rise. Changes in crank length on this recumbant will be entirely compensated with horizontal movement and 0 height change.

Futher reducing the up adjustment necessary when shortening cranks, and especially if the cranks are a lot shorter, pushing the saddle back may be necessary to keep the knee/pedal relationship the same. Unless you want a more triathlon like position, that is...

So seemingly paradoxically, the more you shorten the cranks, the less you need to move the saddle up because you need to move it back more to maintain the same knee/pedal relationship.
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Old 01-31-22, 03:33 AM
  #94  
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Originally Posted by Polaris OBark View Post
After reading this thread, I ordered a 165mm crankset. It will be interesting to compare it to my 172.5mm one that is otherwise identical.

One thing has me a bit worried: Presumably I will need to raise the seat-post by 7.5 mm. The bike was custom-build around my sizing and presumably with the 172.5mm crankset in mind. I wonder if the bike will handle any differently. Presumably the saddle to bar drop will be the most significant change.

This experiment is primarily motivated by pedal strikes off-road with my 650b wheels (which also presumably alter the original intended geometry of the framebuilder).
It's more complicated in terms of saddle height changes, and depends on frame geometry and you saddle setback preferences. I just posted a reply to another post here about this relationship, then saw yours on a similar topic!

Edit: yes bar position will change too, but I would fist figure out the seat position and the see what you need to do to maintain a similar ridinbg position relative to the bars
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Old 01-31-22, 03:35 AM
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Originally Posted by Polaris OBark View Post
After reading this thread, I ordered a 165mm crankset. It will be interesting to compare it to my 172.5mm one that is otherwise identical.

One thing has me a bit worried: Presumably I will need to raise the seat-post by 7.5 mm. The bike was custom-build around my sizing and presumably with the 172.5mm crankset in mind. I wonder if the bike will handle any differently. Presumably the saddle to bar drop will be the most significant change.

This experiment is primarily motivated by pedal strikes off-road with my 650b wheels (which also presumably alter the original intended geometry of the framebuilder).
That's the intuitive view, but it depends how you currently set up your saddle height. In the article I linked to above, the fitter actually suggests starting with the same saddle height as you previously had with longer cranks. This reduces both leg extension at the bottom and hip closure / knee bend at the top by equal amounts i.e. the centre of rotation remains the same, with reduced extension and compression. Depending on your functional range of flexibility, either one or both of these reductions could be beneficial. Once you get a feel for the change you can then tweak the saddle height to optimise. But remember that the main benefits of a shorter crank are the reduced extension and compression angles throughout the pedal stroke. It is of particular benefit to anyone with limited flexibility in one or more joints i.e. most people!
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Old 01-31-22, 03:52 AM
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Originally Posted by cubewheels View Post
You got it. The gradient will give you a "pull" and your setup will affect how that pull will increase or decrease your riding comfort.

If I'm just going to have 1 hour ride doing loops in the hills, I'm going to tilt my saddle down at home before I leave. For >2 hour rides with plenty of flats, I'll keep the saddle level.

Tilted down saddle can be uncomfortable on long descents obviously. One way I deal with it, is stand over the down pedal but without changing my arm position so my butt is still over the saddle and still hunched down in an aero position. The position relieves pressure on the hands and butt and is a very comfortable position to descend.

This is one extreme example of a bike setup for Hill Climb Championship, note the maximum forward position and saddle tilted down. I suspect the event will be involving some long very steep climbs that's why the saddle is tilted that far down.

This is my solution. I think it works well for both flats and climbing. I just set the forward part of the saddle horizontal and the tail is angled 9 deg downward. I don't adjust my saddle setback for climbing, but I have an endurance setup, so my reach is fairly conservative anyway. I can see the logic in it though.

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Old 02-04-22, 04:37 AM
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Simple CAD model

For the fun of it, I put together a simple CAD model to look at how shortening cranks can change fit.

I started a new thread with the model here:

https://www.bikeforums.net/fitting-y...er-cranks.html

After the model, I posted a few interesting things I learned about my set up going from 175mm to 150mm crank lengths.
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Old 02-17-22, 01:41 PM
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When you mentioned your experiences with cramps on a 175mm crank, that's a perfect indication that 175mm was for sure long for you. Although we have to consider that you are more physically fit during the time you did the climb on a 170mm, there's no getting away with "standard" human biomechanics.

To know the reason why everybody talks about opening up the hip and the relief that comes with it, we have to understand that our Quadriceps put so much force when cycling. Although our glutes help extend our legs when pushing down the pedals, it only serves to stabilize the hip and the initial movement. Our Quadriceps need to be at an optimal angle to generate a lot of force without breaking down a lot of energy.

The length-tension (L-T) relationship of muscle basically describes the amount of tension that is produced by a muscle as a feature of its length. And in the case of the quadriceps, it is strongest at 110-120 degrees of knee extension. Given that number, shorter cranks are beneficial because it positions the Quadriceps (in relationship to the hip as well as the knee) at an angle that generates a lot of force without really breaking down a lot of energy, especially at the top of the pedal stroke where most of the force is generated to move forward.

So going back to your cramps and your relief:
175mm: Closed Hip --> Suboptimal angle for Quads during the force-generating phase of the pedal stroke (11 o'clock to 3 o'clock) --> More energy to break down for the Quads to generate force --> Tired Quads --> Cramps
170mm: Opened Hip --> Optimal angle for Quads during the force-generating phase of the pedal stroke (11 o'clock to 3 o'clock) --> Less energy to break down for the Quads to generate force (simply because of its efficiency) --> More enduring Quads --> No Cramps --> Sustained Power


One practical example for this: When you're doing a full squat, it's so much harder to overcome the force when your buttocks are all the way down to the floor with your knees fully flexed but when you reach 110-120 knee extension, or when you're almost in a full standing position, it's just so much easier to manage the weight. That's not because the weight your carrying was 100lbs heavier, but during the phase where your knee was fully flexed, the muscles that are responsible for generating the force aren't at an optimal angle.

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Old 02-21-22, 11:20 AM
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Originally Posted by mattraw View Post
When you mentioned your experiences with cramps on a 175mm crank, that's a perfect indication that 175mm was for sure long for you. Although we have to consider that you are more physically fit during the time you did the climb on a 170mm, there's no getting away with "standard" human biomechanics.

To know the reason why everybody talks about opening up the hip and the relief that comes with it, we have to understand that our Quadriceps put so much force when cycling. Although our glutes help extend our legs when pushing down the pedals, it only serves to stabilize the hip and the initial movement. Our Quadriceps need to be at an optimal angle to generate a lot of force without breaking down a lot of energy.

The length-tension (L-T) relationship of muscle basically describes the amount of tension that is produced by a muscle as a feature of its length. And in the case of the quadriceps, it is strongest at 110-120 degrees of knee extension. Given that number, shorter cranks are beneficial because it positions the Quadriceps (in relationship to the hip as well as the knee) at an angle that generates a lot of force without really breaking down a lot of energy, especially at the top of the pedal stroke where most of the force is generated to move forward.

So going back to your cramps and your relief:
175mm: Closed Hip --> Suboptimal angle for Quads during the force-generating phase of the pedal stroke (11 o'clock to 3 o'clock) --> More energy to break down for the Quads to generate force --> Tired Quads --> Cramps
170mm: Opened Hip --> Optimal angle for Quads during the force-generating phase of the pedal stroke (11 o'clock to 3 o'clock) --> Less energy to break down for the Quads to generate force (simply because of its efficiency) --> More enduring Quads --> No Cramps --> Sustained Power


One practical example for this: When you're doing a full squat, it's so much harder to overcome the force when your buttocks are all the way down to the floor with your knees fully flexed but when you reach 110-120 knee extension, or when you're almost in a full standing position, it's just so much easier to manage the weight. That's not because the weight your carrying was 100lbs heavier, but during the phase where your knee was fully flexed, the muscles that are responsible for generating the force aren't at an optimal angle.

*bow*

Human body over the years: Correction --> Adaptation --> Evolution

I love the PNW!

I'm a Med student by the way.

Sources:
Anatomy, Physiology, and Neuroanatomy by Snell
Braddom's Physical Medicine and Physical Rehabilitation
Physical Rehabilitation by Sullivan
Great first post! I like the squat analogy. Shorter cranks just make it easier to control those critical angles at both the top and bottom of the stroke. If cranks are too long, you can run into trouble at both ends of the stroke i.e. too much knee bend at the top and over-extension at the bottom. As an endurance cyclist I strongly favour shorter cranks for this reason, although fortunately my legs are long enough to cope fine with standard cranks lengths up to 175 mm. But I do prefer slightly shorter.
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Old 04-26-22, 08:21 AM
  #100  
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There is no general answer or rule to this because there are so many variables with the rider's size, proportions, weight, and the conditions and length of a race or ride, and even psychology comes into it. The only sure way to know for each person is with objective testing with stationary equipment or measuring on course performance. The answer will even change for each rider as their fitness becomes more or less, their age etc..

If someone dares to think they can be psychologically objective and test their current performance on a course or testing equipment with different length cranks, frames etc.. then they might get some answers, otherwise probably none that will make a performance difference. It is like someone believing their car will have more power because someone else told them if they bolt on this "hot rod" part that is what will happen, but a real tuner of racing engines will tell you absolutely that unless it is proven on a dyno or on the track the talk means nothing.
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