Crank Length After fitting, Question.

[Shortsocks]

Hey Folks.

So I went and had a Professional Fitting update done for my new Rig. Everything was pretty good. Except they put me on a 170mm crank, except I actually really like the 175mm Cranks. I'm not tall either. 5'9 32.5 inch inseam.

So I've been reading a lot about crank Lengths, pro's and cons. Also bike fittings and Crank length.... What I've come to the conclusion is that pretty much Crank Length is a Preference because I've been riding a 170mm and I cant stand it. I mean I wouldn't mind it if I didn't come from my 175mm.

So The question is, Is crank length just a preference for you guys/gals or do you folks go by your fitters advice strictly?

[Dave M]

I'm about your size and prefer 170 over 172.5's. But I think its really just a preference issue. The data seems to suggest crank arm length does not really affect efficiency and power. I say ride what you like.

[oldpotatoe]

Hey Folks.

So I went and had a Professional Fitting update done for my new Rig. Everything was pretty good. Except they put me on a 170mm crank, except I actually really like the 175mm Cranks. I'm not tall either. 5'9 32.5 inch inseam.

So I've been reading a lot about crank Lengths, pro's and cons. Also bike fittings and Crank length.... What I've come to the conclusion is that pretty much Crank Length is a Preference because I've been riding a 170mm and I cant stand it. I mean I wouldn't mind it if I didn't come from my 175mm.

So The question is, Is crank length just a preference for you guys/gals or do you folks go by your fitters advice strictly?


Preference and ‘feel’, subjective. Put 3 people in a room and ask about crankarm length, get 4 opinions. If ya like 175, use that realizing that you’ll have to lower saddle 5mm compared to 170mm.

[merckx]

Don't be oppressed. Use what you desire.

[ripvanrando]

I've used 170 mm all the way to 200 mm cranks but generally like 175 or 177.5 mm best.

Good arguments to use short cranks on TT. Hip angle and being able to get more aero.

175 mm is a bit long for a short rider but if they feel good, why not?

[cmbicycles]

The most economical solution is to just buy another identical bike and set both up identically except for cranks and then you can compare back to back and see what you think with absolute accuracy. ;)

You have the benefit of thousands of miles over varied terrain on which to base your preferences. Your fitter likely doesn't have much of an idea how you ride your bike in the real world, and has only seen you on a trainer for 1/2 hour +/-. I would err on the side of you vs. your fitter, but maybe give the others a couple weeks to give them a fair shot as many fitters make recommendations based on averages and feedback over time... you still may be on one side of the bell curve instead of the middle. If after a couple weeks you still prefer the 175, swap them back and adjust the saddle appropriately.

[echelon_john]

Hear that? That's the sound of a pendulum swinging back.

[muz]

I typically ride 170's, but have bikes with 165 to 175 mm cranks. Darned if I can tell the difference, and I ride long distance (up to 1200 km). It's only 5mm, less than 3% difference.

[LouDeeter]

If you like 175, go with it. In my experience, the longer crankset causes more hip range of motion. On hard or long rides, that can cause soreness, particularly if you don't stretch your upper legs and hips frequently. Otherwise, I remember Sheldon Brown offering convincing arguments that the "leverage" one would intuitive get from a longer lever arm (crank) is not true. He and I discussed this and he did somewhat agree that it is possible to get the leverage from a longer crank when out of the saddle, but not in it. I don't know. And, the old argument was that a shorter crank arm allowed you to spin more, while a longer crank arm was for someone who like to grind in a lower RPM. We're talking about 1/2 cm of course, which isn't much in the grand scheme of things.

[Kontact]

It is more preference than not, but there is a point when a crank can be so long that it is putting unnecessary stress on your body. There doesn't seem to be a corresponding too-short problem.

But don't ride something you 'hate'. Consider 172.5, though.

[Bob Ross]

It is more preference than not, but there is a point when a crank can be so long that it is putting unnecessary stress on your body. There doesn't seem to be a corresponding too-short problem.

Interesting premise. If I try to imagine what it would feel like to ride extremely short (like, comically ridiculously Circus clown short) cranks I feel like my knees would get unnecessarily stressed.

But that's not a realistic scenario, so...

[Ralph]

You don't always ride on the same cog when comparing and talking about crank arm length. Sure....longer cranks (levers) give more leverage. But from your high school physics class (levers and pulleys) .....a larger pulley (cog) also does that. So at 5' 9" if a 170 arm fits your body (femur length mostly) better than a 175, you can gain all the leverage back and more going one cog larger in rear. One cog larger, for most combinations, is a bigger percentage change than crank length from 175 to 170.

Same with riding real short cranks. Just be in the gears you need for the leverage you need. Maybe spin a little more. You give up nothing....if the cranks fit you.

Your fitter is probably correct after measuring you. But it may not make any difference in your riding if you're not feeling it. Ride what you want. But I think your fitter is probably correct in theory.

Sure the guy on 175's may climb a steep hill in a 30 tooth cog, and the guy on 170's may use a 32 to gain about the same leverage.

[Black Dog]

There is some good research on this, nut not a lot of it. However, it seems to show that shorter arms allow for better overall power production all else being equal.

Here is a synopsis from Training Peaks (https://www.trainingpeaks.com/blog/the-benefits-of-reducing-your-crank-length/) Web site:

Crank Length
When I present on the topic of crank length, I begin by asking where crank length came from. Where did these lengths that we consider “standard” originate from? There are some theories dating back to the origin of the first push bike, or the length that was optimal for the penny farthing bike (bike with a large front wheel and small rear wheel). Most likely, crank length has just been passed down from one generation to another and over time has just become accepted even though there is no basis for the current “standard” with the current bicycles we ride today.

There has been a lot of great research lead by Jim Martin and John McDaniel on the topic of crank length. During the initial study, Martin1 looked at max power and found there was no difference between 145 to 195mm crank lengths, he did note that there was less oxygen (O2) uptake with the shorter cranks.

In the next step, McDaniel et al.2 looked at efficiency and setup a study where cyclists used crank lengths of 145, 170, 195mm, where cyclists pedaled at 40, 60, 80, and 100rpm, at an intensity of 30, 60, and 90 percent of blood lactate. The results showed that O2 uptake increases as pedal rate increases. It’s important to note that pedal rate is not cadence and is defined as the speed of the pedal along it’s axis.

An easier way to think of this would be would be if you took two athletes and placed them on the track. One in the inside lane (we can call this the 145mm crank) and one in the outside lane (the 195mm crank) and both athletes had to run 1 lap (revolution) in 1 minute 30 seconds. The athlete in the outside lane has a greater distance to cover and would have to run at a faster rate than the athlete in the inside lane to both complete one revolution of the track. This would be the same as an athlete pedaling a 145mm and 195mm crank at 90rpm. With the 195mm crank length, the foot speed is higher to cover the revolution at 90rpm compared to the 145mm crank length.

Most report that when they switch to a shorter crank, that their cadence increases. It is theorized that the increase in cadence when moving to a shorter crank length isn’t due to trying to make up for the lack of leverage, but to replicate the foot rate/speed an athlete is accustomed to on a longer crank and to use the extra available O2, which is minimal.

[Ken Robb]

I almost always have ridden 175. I got one bike with 172.5 and couldn't tell any difference. I got a bike with 180 crank and, at first, loved it because I could muscle up hills in a smaller cog though I didn't think I could spin them as fast (RPM) as my 175 cranks. After riding this way for a while I got twinges in my knees so I went back to my 175. Also at this time I got an old bike with Nuovo Record 170 cranks. Like most of my bikes this was a 60cm frame. I could feel that I was pedaling smaller circles and I rode a bigger cog than I would when riding 175 but I was comfortable with that. I think I could learn to love 170mm cranks.

I can hypothesize that shorter cranks might keep our legs in a range of motion (less flex) where we can produce more power (torque) than when we are turning bigger cranks with more knee flex. In an extreme example think about how little power one can generate when sitting on a saddle that is way too low keeping your leg in a position of extreme flexion and you never get near fully extended.

These are just unscientific observations by an old man with no training whatsoever in anatomy or sports medicine. I really wanted to write "kinesthesiology" but I couldn't spell it. :)

[carpediemracing]

I have very short legs (approx 28.5" inseam) yet I found, the hard way, that 175s work better for me.

I've also learned that I'm basically all anaerobic and even my sitting in technique involves smashing the pedals for about 1/4 revolution to close little gaps, and soft pedaling or coasting a lot.

I race and I can't climb or TT due to having close to a zero aerobic engine. However I can sprint, so this pedal punching sort of makes sense.

I tried three times, about 4-10 months each time, to move to 170s, because, on paper, it's better. I could spin more, my legs are short, I ought to be able to sprint faster. It was also much more comfortable when pedaling very easy because my knees didn't come up as high, and since I'm not skinny, my knees would usually have to displace some torso at the top of the pedal stroke.

The reality is that on the 170s I didn't sprint faster, I wasn't as comfortable aerobically in the field (maybe because I had to exert more torque for my quarter revolution gap closing smashes?), and I actually struggled to finish races with the same riders.

I paid money for the shorter cranks, I adjusted my fit, I started on the shorter cranks in typically Oct-Dec the year prior... I was committed to the 170s. Cognitive dissonance alone would have had me loving the cranks. But I simply couldn't get good results with them. I think the latest I gave up was July or August, the earliest was May.

Each time, after a long period of acclimatization, after trying the 170 cranks in races, I would finally give up and move back to 175s. I immediately, and I mean immediately, felt much better.

Since my experiments were with Cannondale SI cranks, I literally only changed the crank arm itself. Spider was the same, pedals, etc. I dropped the saddle 5mm when I went back to the 175s but that's about it.

I can tell you the long cranks don't help at all when climbing very steep hills out of the saddle. I do like them on power climbs, where I'm rolling a big gear over moderate grades (3-5%).

So it's all about preference and matching the cranks to your physiology/style.

[11.4]

I've launched more than a few discussions about crank arm length, coming from the track world, and there are some interesting issues to consider.

Most of the studies are largely worthless. Typically this is because they take an ergometer, put the athlete on it, and simply change the crank arm length without other changes and without allowing riders to become fully acclimated to the new lengths. What are the issues? First, by only changing the crank arm length, your degree of knee flexion changes quite a bit. In the pedal stroke, the calf is just along for the ride; the geometry is determined by the length of the femur. As your cranks shorten, your 3 o'clock position brings the foot closer under the body, increasing the knee flexion (and for those who worry about such things, changing the KOPS position). One has to change the fit completely with a change in crank arm length. Second, some riders acclimatize immediately to different fit parameters but others need quite a bit of acclimatization. That's also why previous posts on this thread are so much in conflict with each other on the issue.

Second, adjustments for crank arm lengths aren't always logical. If you reduce the crank arm length 10 mm and drop your saddle 10 mm, the center of rotation of the pedal stroke has been reduced 10 mm. And the top point on the pedal stroke has reduced by 20 mm. Your individual needs may require this, for example to avoid thigh impingement with the diaphragm or to deal with limited hip mobility, but it isn't arbitrarily correct. I usually keep riders at the same saddle position when they reduce crank arm lengths and sometimes will do so when they extend the length. The center of rotation is ignored by most testers and fitters, but it isn't trivial. Your legs are used to scribing a circle with a particular center, not just a particular top or bottom point. Add to that that if you drop the crank arm length by 10 mm, you are effectively pulling your pedal position back 10 mm relative to your knee, so you may need to move the saddle back, which then throws into play all kinds of issues about hip flexibility, rotation, back rotation, and so on.

Another point to consider is how foot action (ankling and the like) changes with changes in crank arm length. When you shorten your crank arm length, you're probably having to throw a bit more range of flexion into your pedal stroke, especially if you increase cadence. As soon as you do that, you absorb or expand part of the change in effective crank arm length. The change is dependent on how you already pedal and your own morphology, but it does change.

In short, it's all an interacting system. You can't dissect one dimension like crank arm length and ignore the others. Every individual is different, and these two facts are why you really just have to try it for yourself. Trying to emulate someone's crank arm length is like trying to emulate their saddle height. It just doesn't work.

[Ti Designs]

If you're smart enough to understand how the body reacts to something like a crank length change, you're smart enough to go into some line of work that isn't bike fitting and pays far better...

So I'm answering this as an idiot.

Now that we got that out of the way, we need to look at the hardware and firmware. The hardware is the bike, or in this case the crank, and the fixed distances of the body, also known as range of motion. The firmware is all the motor skills you've gained, plus your reflexes. You have two limits on range of motion here, the top of the pedal stroke where you're closing hip angle, and the point where the pedal is furthest from the hip (around 5:00). The danger of going past these ranges of motion isn't that tiny distance that you're past, it's the body's reflex action to going there - in both cases it's pretty bad. At the bottom, if your saddle is too high or too far back, you run out of range of motion some time before the pedal gets to 5:00, the pedal gets pulled down, that tugs on the anterior tibialis. Your muscles have a defense for that, it's call a pull reflex. Every time your pedal gets just past you're range of motion, your body is tugging back. Here's the funny thing (if injury was ever funny) your body limits what you can do with your muscles, but not it's own reflexes. When your anterior tibialis pulls back it's not holding anything back - it's a reflex. Unlike walking where your foot isn't attached to anything, there's no strain relief on the bike. The bike is solid from the pedal to the crank to the frame to the seat post... There's a huge spike in tension caused by going 1mm past your range of motion.

The limit on hip angle is just as critical if not more so. Being outside your range of motion means moving the SI joint 80 times a minute for as long as you're on the bike. The list of things going wrong is really long...

The firmware is what you've learned over your life about how to use your body - it's called motor skills. I'm not going to agree with the statement that shorter cranks are better for higher RPMs because I've done my homework. Your body has defenses against changing certain things. Your body would always rather push longer than push harder - that's how you prevent injury. In walking, you would think it would be easy to walk faster just by increasing your step rate. It's not, the body wants to increase the stride length. So, you're a machine that wants to change stride length and the bike allows for changes of cadence, but the stride length - the crank length, is fixed. It's a bit of a mismatch.

Crank length isn't a simple question to answer. It's about limits of range of motion and what skill sets to can learn to handle a wide range of cadence. I'm going to end here, because anything beyond this can't be general information, it has to be about an individual pedaling a bike.

[Shortsocks]

I have very short legs (approx 28.5" inseam) yet I found, the hard way, that 175s work better for me.

I've also learned that I'm basically all anaerobic and even my sitting in technique involves smashing the pedals for about 1/4 revolution to close little gaps, and soft pedaling or coasting a lot.

I race and I can't climb or TT due to having close to a zero aerobic engine. However I can sprint, so this pedal punching sort of makes sense.

I tried three times, about 4-10 months each time, to move to 170s, because, on paper, it's better. I could spin more, my legs are short, I ought to be able to sprint faster. It was also much more comfortable when pedaling very easy because my knees didn't come up as high, and since I'm not skinny, my knees would usually have to displace some torso at the top of the pedal stroke.

The reality is that on the 170s I didn't sprint faster, I wasn't as comfortable aerobically in the field (maybe because I had to exert more torque for my quarter revolution gap closing smashes?), and I actually struggled to finish races with the same riders.

I paid money for the shorter cranks, I adjusted my fit, I started on the shorter cranks in typically Oct-Dec the year prior... I was committed to the 170s. Cognitive dissonance alone would have had me loving the cranks. But I simply couldn't get good results with them. I think the latest I gave up was July or August, the earliest was May.

Each time, after a long period of acclimatization, after trying the 170 cranks in races, I would finally give up and move back to 175s. I immediately, and I mean immediately, felt much better.

Since my experiments were with Cannondale SI cranks, I literally only changed the crank arm itself. Spider was the same, pedals, etc. I dropped the saddle 5mm when I went back to the 175s but that's about it.

I can tell you the long cranks don't help at all when climbing very steep hills out of the saddle. I do like them on power climbs, where I'm rolling a big gear over moderate grades (3-5%).

So it's all about preference and matching the cranks to your physiology/style.


This is pretty much Exactly what I went through. To the "T".
Thanks for all the responses. I'm going to put on my 175mm's and go to the Fitter next week and get him back to work. Its amazing how much of this is preference, and there really is no rhyme or reason to it. We just like what we like sometimes.

I guess thats the the great thing about life. Logic is surpassed it seems.

[11.4]

This is pretty much Exactly what I went through. To the "T".
Thanks for all the responses. I'm going to put on my 175mm's and go to the Fitter next week and get him back to work. Its amazing how much of this is preference, and there really is no rhyme or reason to it. We just like what we like sometimes.

I guess thats the the great thing about life. Logic is surpassed it seems.

Not necessarily preference or randomness. It's founded in the complexities of how your body operates and the uniqueness of that. There's a huge thread somewhere on this that Ti and I both like (and mouthed off in, of course). My general point is that each person has a certain range of motion in which they can change crank arm lengths, saddle heights, whatever, and do fine. Get them past that and their performance drops fast. Sometimes that happens not because of something like basic leg length, but because you've shifted your knee flexion angle, your range of hip motion, whatever. It's why I generally recommend not changing saddle height with a change of crank arm length; try to acclimate to a new length with the same center of rotation before selectively making other changes. Some people have problems with crank length changes simply because they are already positioned off the middle of their comfort range and are impinging on points where they can't pedal effectively; others have a very narrow usable range; others have other positional issues that most fitters don't recognize or address. Again, it's an experiment of one and you have to figure it out for yourself.

[wallymann]

...but i was a better sprinter with 170s.

[carpediemracing]

A brief note.

I adjust saddle height when changing cranks because my sensitive/fragile? knees hurt otherwise. I tried the longer cranks without moving the saddle but that ended pretty quickly. Leg extension for me seems to be critical so saddle height is a critical measurement. How far up my foot comes doesn't seem to matter (hips, knees, etc) except when I'm really heavy and I end up kneeing myself in the gut.

To be fair I often sit with my legs under me, my heels under my butt, for long periods of time, so my knees are okay with being "closed", so having my foot come up high isn't going to hurt me. I know some people can't sit like that.

I 100% prefer the "feel" of the shorter cranks. Higher up position, no torso clearance problems, feeling like being more over the bars, knowing I can pedal deeper into corners, the feeling of exerting a lot of force (like narrow bars, which I like to some extent), etc. But for some reason they just don't work for me. I slap the 175s on, the saddle drops, bike feels much less racy, but I'm contesting field sprints for wins rather than struggling just to finish (same courses, similar rider composition, and all my tricks to getting to the finish in reasonable shape).