GamblerGORD53

I have an old Rudge, which used to all have 7 1/8 ... 182 mm. My old Raleigh 5 spd had gutless 165s.
4 Years ago I got a SA 5w and first used it 3 times with those 165s. Then I got a new crank with 180s. Instantly had the 9% more power, especially up hills. I can still wiz it up, which is the best way for speed. I am just 5' 8". Went 4200 miles on tour with it and a Rohloff.

With a derailler it is just lost in the gearing. 165 does now feel knuckle toed by comparison.

AlmostTrick

I'd say the most comfortable/efficient crank length for a particular rider corresponds to their leg length and preferred cadence.

Persons with longer legs will usually feel better running longer cranks. But it's harder to spin a longer crank as fast as one could spin a shorter one, so persons who like spinning higher RPM's will often feel better with a shorter crank. So it's a balance of the two. This is why you really have to try different sizes for yourself and see which you prefer.

I'd also say the popular 170mm length is likely ultimate, or close to ultimate, for a high percentage of riders.

McBTC

While there is not a lot of research in this are, the little that does exist supports going to less than 160 cranks even for longer legs. The mass component market doesn't support shorter cranks and 165s are about all that's easily available but even 165s are not found in any standard setup except on the smallest road frame. Even so, shorter cranks may be the more efficient setup. For some, as low as 145 may be the most efficient setup and even shorter may be no less efficient than going longer. Learning that is the case if not easy because changing crank size is not as easy as changing gears. Crank lengths in the 170s probably is no more ideal than longer versus shorter stroke gas engines or thinking carbo loading is necessary before a long ride.

HillRider

Where did you read this? I've never heard of any studies to support it.

This is certainly off-topic but shorter stroke length, within reason, is a better design. It allows higher rpm without excessive piston speed and allows for larger valves (due to the larger bore diameter) for better, more efficient breathing. The only reason for a long stroke is when tax laws are based on bore diameter (not just displacement) as the British laws were years ago or to make the engine more compact when there are packaging concerns.

Excessively short strokes, like F1 engines, do have issues with emissions due to extra surface area but for most uses, shorter is better. However, I have no reason to think that applies to crank length.

fietsbob

Seems 165 cranks are used on Track Bikes, so if you are not at full speed

the up slope foot and pedal wont hit the Banked track.

dim

here is a good article:

https://www.analyticcycling.com/Pedal...ngth_Page.html

AlmostTrick

How does this research deal with the fact that a longer crank offers more leverage, and therefore more torque? So while a rider may not be able to spin a longer crank as fast, he/she doesn't have to because the increased leverage allows them to gear up a bit. This is why it seems to me it comes down more to personal preference.

I remember reading a study a while back that showed shorter cranks offered more performance, and while it's fuzzy in my memory now, it seems it had something to do with the amount of oxygen used by the rider.

If you have links please post.

McBTC

For most power using 145s* see--e.g.,

"...a study** done by Jim Martin at the University of Utah (Determinants of maximal cycling power: crank length, pedaling rate and pedal speed). What did this study show?"


Ref: https://www.powercranks.com/cld.html


**Jim Martin's study (University of Utah) is used by manufaturers to justify making fewer options available, but the research showed that going as low as 145mm may actually help put you closer to your peak efficiency.


* https://www.ncbi.nlm.nih.gov/pubmed/11417428





Personally, my experience on training equipment has seen steady improvements in both pace and cadence going to 106 mm cranks.

rydabent

+1 A longer crank arm means more torque. Torque is what turns the wheel.

HillRider

You own experience negates that data which shows a significant fall off in power as the crank length goes below 120 mm. Oh wait, did you mean 160 mm cranks?

Anyway, that limited data in the study you referenced showed an insignificant difference between 145 and 170 mm cranks. I also wonder what the sample number of riders tested was. Lots of poorly controlled studies get published showing what the sponsor wants to show.

McBTC

True, while Power produced with the 145- and 170-mm cranks was significantly (P < 0.05) greater than that produced with the 120- and 220-mm cranks, according to the study, 145s were not found to be significantly greater than 170s. Even so, the study does reinforce my personal experience that 175 (even 180) -- as convention would be suggest is appropriate for someone my size -- is not the most efficient crank length and that sub-145 is even better based on maximization of wattage. The error bars are interesting to consider since they represent the variability that exists among individuals. Unfortunately, it's difficult for individuals to work with this variable so most riders are pretty much stuck with adopting the consensus view about these matters, whether they question it or not. Triathletes are an exception to the extent that more of them as a percent are interested to see if their personal experience might challenge the conventional wisdom; and for those who have, some apparently have benefited from going to shorter cranks, for reasons that are in addition to whatever improvements in efficiency might be realized (e.g., seeing an improvement in run times after completion of the ride-part of the competition).

dim

bottom line ... the faster the front crankwheel turns, the faster the bike travels (assuming that you remain using the same gearing) ....

so if you have a faster cadence/rpm's using the same gearing, then you faster ... a shorter crank gives you a faster cadence

correct me if I'm wrong

McBTC

You're right: in any given gear, >rpms = >pace.

HillRider

That's a big if. If you can turn a faster cadence using the same gearing then certainly you go faster.....but you need to generate more power to do it and maybe you can and maybe you can't. A shorted crank does not give you a faster cadence, particularly against increased resistance. It may allow some riders to spin faster but they may also need a lower gear to do it.

noglider 

It's hard to believe that people can feel differences in crank lengths when the differences are so tiny, but some of us can. When I get on a bike with 172.5 cranks, something feels a little weird. On a bike with 175s, I just can't get comfortable.

That may have something to do with my physique. I have short thighs and long feet. One of my bikes has 155s! It doesn't feel strange to me at all. In fact, it doesn't feel different than 170s except that it requires me to raise the seat a bit so I can straighten my legs at the bottoms of the pedal strokes. This puts my center of gravity a little high, and that's what I'm really feeling.

AlmostTrick

Don't forget, the shorter crank will have less leverage and therefore require more force to turn it. (in the same gear)

McBTC

...in theory, perhaps; and,

however, in reality...

...with the resulting lower foot speed comes countervailing benefits that more than compensate for these variables, at least for those who experience greater efficiency going to a shorter crank. The greatest benefit will be for those for whom shifting to an even higher gear feels completely natural when going to a shorter crank.

HillRider

And who might that be? So you tell me that lower leverage with the crank will allow higher gear at the same time?

McBTC

If it enables the rider to achieve a more aerodynamic position, that's a freebee but in addition to that, the powercranks link above also talks about pedal speed and knee leverage, although less scientific than Martin's work, as follows:The article also discusses the results of the personal experimentation of others who sorted out in the 130-150 mm range and the personal experience of the 6'2" author (with a 34" inseam) who has experimented with cranks as short as 85 mm and believes his optimal crank length to be 130-145.

GamblerGORD53

The underlying and undeniable scientific principle involved is ... What is gained in force is lost in distance. Newton's Laws.
181.5 is 10% more than 165. Me with the long crank will do 90 revs for your 100. Our TOES will be going EXACTLY the same speed along our respective circumference of motion. My knees will be pushing at 10% less weight than you. So I don't see how knee strain is a factor. I can see how high revs do help in high speed applications.

jyl

Browsing through studies, it seems that, other than at extremes, crank length doesn't make a significant difference to power.

That is the conclusion of the Martin study quoted above. Determinants of maximal cycling power: crank length, pedaling rate and pedal speed. - PubMed - NCBI

And also two more studies:

Effect of crank length on joint-specific power during maximal cycling. - PubMed - NCBI

"These data demonstrate that crank length does not affect relative joint-specific power once the effects of pedaling rate and pedal speed are accounted for. Our results thereby substantiate previous findings that crank length per se is not an important determinant of maximum cycling power production."

Effects of crank length on maximal cycling power and optimal pedaling rate of boys aged 8-11 years. - PubMed - NCBI

"Power produced when using the 170 mm cranks [mean (SEM)] [364 (18) W] did not differ from that produced with the LL20 cranks [366 (19)]. Optimal pedaling rate was significantly greater for the LL20 cranks [129 (4) rpm] than for the 170 mm cranks [114 (4) rpm]."

However, it seems there are some potential differences:
- Shorter cranks require higher cadence to get the same power as longer cranks. So if you prefer faster or slower cadence, you might prefer shorter or longer cranks.
- Shorter cranks require less range of motion at the leg joints. So if you already have limited ROM/flexibility, or conversely if you are worried about losing ROM/flexibility (use it or lose it), you might prefer shorter or longer cranks.
- Shorter cranks keep your knees lower at the top of the pedal stroke, which could permit a flatter back, so depending on flexibility and tibia/femur length, and on your need to ride in an aero position (TT or climber?), you might prefer shorter cranks.
- Shorter cranks require lower gearing, so depending on whether your lowest gearing needs to be and/or can be made lower (like, are you already using the lowest gearing your bike can have, to climb), you might not prefer shorter cranks.
- Shorter cranks require a higher saddle, which may result in a more rearward saddle, and possibly some setback adjustment.

According to the 20% of leg length formula that some propose, I should ride 165 mm cranks. I'll keep an eye out for cranks in that length (that I'd want to see on my bike . . . )

Come to think of it, I've previously had occasion to drill holes in a solid alloy crankarm, and it was pretty easy using a drill press. I suppose I could buy a cheapish crank, drill and tap a bunch of holes, and experiment away, without spending several hundred dollars on "adjustable" cranks that weigh 1000 g (PowerCranks etc).

Jamminatrix

The reality is that if there was one perfect length, everyone would be using it. Teams, sponsors, and manufacturers of the industry all spend millions of dollars every year on developing technology and looking for seconds. And so far, there's still no conclusive evidence other than personal preference - that seems to *generally* correlate with rider size.

Torque only starts. Horsepower is what maintains.

You've neglected deflection of joints, ligaments, and muscles increasing.

McBTC

Not sure what you're saying about revs or what you mean about "knee strain" but it must be consistent with the fact that in any given gear, the longer the crank the greater the foot-speed. The greater the circle described by the arc of the pedal the more distance the foot must travel per revolution.

Maelochs

If the crank does not reach from the spindle to the pedal, you will find your performance compromised.

Maelochs

On a more serious note, I think torque is a big issue, which is why MTBs and tourers tend (IME) to offer longer cranks---getting all that mass moving, or doing so on rough surfaces. other than that there is an issue of comfort ... I have relatively long legs. I used to feel more comfortable with 175s. Now I am older, weaker, and used to 170s, and my 175s feel a little long ... but i doubt I would notice after half-an-hour.