After years of riding different types and styles of bikes, the variance of crankarm lengths is notable when pushed hard. For me, I like to ride everything but regarding crank length and determine what's appropriate, I use a 'feel' by how much the knee pains. I leave the math for the rest of it.... wheels, chainring, gearing, etc.. If the knee's really feel it, I'll change out for a shorter crank arm. Might seem odd but usually works for me. Also, as we age our joints naturally degrade and progressing to using shorter crank arms does help.

OK, I have thought of some corollaries to your assertions, Rudi. A rider, with his particular physique and conditioning X (strength, power, endurance), expecting to ride in a certain style Y (cadence, speed, speed range) , over a certain terrain Z (hilliness, traffic (insomuch as traffic affects the rider's speed and cadence variations), wind, distance to be traveled) should have an optimal crank length L. Changing X, Y, or Z might change L. So I guess the idea is to estimate your lowest cadence and your strongest impediment (snow, hill, headwind, baggage), and then figure how low you're willing and able to pedal safely and comfortably.

Maybe those are just rewording what you're saying, rather than corollaries?

With all due respect, your reply does not make sense to me. The study ran riders of various heights though a progressions of crank sizes from quite short to long and found a very small difference in pedaling efficiency. There may be other reasons to select a specific crank length, such as alleviating knee pain, but this study indicates pedaling efficiency is not one of them. Moreover, it states that one can pick a favorite crank length without concern for losing too much pedaling efficiency.

I think efficiency is not as important as comfort and reducing the risk of injury. We achieve greater efficiency if we mash very tall gears. The trouble with that is that our knees won't last long enough for us to be pedaling into old age. This is one reason -- but not the only reason -- experienced cyclists encourage high cadences.

A more useful question is: Given the desire to spin fast, what is the crank length that is most comfortable and useful?

Road racers and mountain bike climbers don't want to spin as fast as commuting riders and club riders. Road racers need to get up a hill fast and use the last bit of strength they can muster. Maybe 175's are good for racers from 5'7" (170 cm) through 6'0" (183 cm).

The rest of us should probably be using 170's at most and probably a lot shorter.

An off road rider needs to add force rather suddenly when encountering a mushy surface or a short steep incline. The ability to do that is important enough to sacrifice a high cadence. Furthermore, I imagine a steady cadence isn't all that likely when riding off road.

noglider- another idea: https://store.cycledifferent.com/mm5/..._Code=ADAPTIVE

But for a basic test, use a trashed long arm crank, further in towards the BB drill / tap to pedal threads.

If you look at the study, you will see large gaps in the crank arm sizes, enough for the ideal length for a particular rider to be skipped over. 'Hasty Generalization' is a logical fallacy (the use of any logical fallacy in an argument indicates a good bet that the conclusion is erroneous) wherein the sample size is too limited to be meaningful.

The difference between the right crank and the wrong one will not be a large value- it may well be only about 3-5%. But in bicycles, that can be a pretty large figure, given how little differences there are in the performance of many components. It can certainly make a difference in a race. More:

https://https://bikesmithdesign.com/Short_Cranks/rom.html

https://www.powercranks.com/

165's get used on Velodromes so the right pedal, on the up-slope-'hill' side of the banked track doesn't hit it

when you are not going fast around the track .. like waiting for your opponent to make a mistake,
and you take advantage of it in a mad dash for 2 laps, in the Matched Sprint events.

FWIW, most of my bikes are 170, one is 171, one is 165, and one is 172.5. I've logged many miles on 170 and 165, would have a hard time telling them apart, but maybe possibly I can imagine that I feel the 165 as smaller. I haven't put enough miles on the 172.5 to comment, but so far it has seemed "normal".

The biggest thing about crank length is how it pairs to the BB height. I first installed the 165 on a bike with a BB 1cm higher than what I was used to. The shorter crank raises the saddle, and that plus the higher BB made me feel higher up off the road. But I put many miles in that configuration and the pedaling wasn't any different than I expected. I've since shifted cranks around to put that crank on a bike with a lower BB, and it made that bike feel more normal.

You are seeing what you want to see. That's called confirmation bias. The Bikesmith Design page is basically anecdotal in nature. I'll take actual science over that any day. The study I linked to states that 170 mm cranks will cost either the tallest and shortest riders 0.5% efficiency at most. That's down in the noise.

I've found shorter cranks to allow more leeway in terms of how hard I can ride early in the season, or when I'm not riding often enough.

I think it's simple to understand how a less-severe bend range in the knee can prevent injury or re-injury.

Very clever.

I tried the using the various fit calculators in the thread, and doing the math twice I should be riding 177.80 - 179.33 cranks. Interesting since I'm way more comfortable (less knee pain ) riding 180's than 175's and felt "awkward" on 170's. As to the "spin to save your knees" instead of mashing argument, if you drop a gear or 2 to lower the force required to turn the peddles at a lower ( mashing ) RPM you also save your knees.........

Yes but eventually, it gets uncomfortable, and you shift back up. We're saying (really hypothesizing) that shorter cranks makes spinning comfier.

plan2peak.com

Why would you want to believe scientific tests using instrumented measurements, many test runs, many test subjects and test data results presented in easy to understand graphics when you should be listening to the personal observations of me and my internet friends?

There is a 1.6% difference in power between 145mm and 195mm cranks. 170mm falls in between and has an even smaller difference between either of them. I don't see how measuring power differences between 170 and 180 is going to yield differences that are greater.

The take away from the study is that if there is optimal crank arm length for you and you don't know what that is, 170mm is going to be at most 0.5% from optimal if you are extremely short or tall, less if you are more normal size. I can live with that.

If you keep reading through that study you will encounter even more heresy with pedaling efficiency that will cause the denizens of Forum 41 apoplexy.

Fortunately we C&Ver's pride ourselves on being able to swing our legs over a wide variety of top tubes and enjoy the ride and savor the difference!

Mark of Bikesmith lives in my town. I've met him and his wife, who is adamant that the shorter cranks made a huge difference for her.

I think that actual science is good too. I am an engineer for my day job. I just don't think this is good science in this study.

Here are the cranks used in that study

120 and 220 mm cranks
145 and 195mm cranks
120, 145, 170, 195, and 220mm cranks

I copied these right from the link itself (which is a series of Power Point panels). I did not even know that 220mm cranks existed, but we can see easily that there are big jumps in the crank lengths used. If we apply the French formula, (20-21% of inseam) its pretty evident that the gaps between sizes are so large that the peaks for most riders probably exist between the gaps. For example, the formula suggests that for me 167mm is ideal and I find I have good power with 165s and 170s. I notice that the 175s are not as easy to go long distances (IOW I can go faster and further with less fatigue if I have a 165 instead of a 175). I don't see a 160mm, 165mm (a common size) nor do I see 175mm. This is what I mean by the gaps are too large. For many riders its likely if they are less than 6' in height that the peak of performance for them exists between 155 and 170, so their peaks would simply not show up with this level of resolution.

In short, the gaps are too large in this study. I think it would have made more sense embarking on something like this if 5mm changes were made. Additionally, this study seems to have ignored the prior information (the French formula)- it could have sought to prove or disprove that at the same time.

Bottom line is it does not seem to present enough data to be useful.

Well, my totally non-scientific opinion is that with my short legs, there is a huge difference in feeling between 165 and 175. I basically cannot ride 175mm cranks comfortably. I have to move the saddle down about 3cm to make it somewhat comfortable--I don't know why, and really, I guess it doesn't matter--but this makes me strongly prefer 165mm cranks. 170 I can tolerate, but I will always choose 165 if available, and if it's not available I will think long and hard about using a different crankset.

I'm quoting you again because I wanted to make sure your questions were answered despite the massive sidetrack of the conversation. Did you?

Thanks everyone. Yes, question most definitely answered. Learned a lot from the sidetrack as well.

Yeah these guys are like the mad scientists of the bike world.. you learn a lot just hanging out here. Glad they could help.

You are assuming that there is a significant peak of performance at a specific crank size in the commonly available sizes. This study shows that for all riders tested, short and tall, there was a neglible difference in power output and efficiency especially between 145 mm and 195 mm. So that magic peak of efficiency can't be very high because the fall-off is low. I think the placebo effect is present when people say they can feel a real difference in power/efficiency in 5 mm delta of crank size.

I have a similar opinion and there's lots of physical variables not being discussed like femur, torso and arm length and bike fit in general. When mtn bikes with horizontal top tubes became popular in the late 80's, 175 cranks were everywhere. The only way I could develop any power was to use a 0 offset post and shove the saddle as far forward as possible. Then I needed super long stems to accommodate my my monkey arms and long torso. Off the shelf bike frames are and were designed to fit people with average proportions and I'm not one of them. 165's allow me a noticeable difference in position and I feel confident I could feel the difference in a blind test on a trainer.

edit

I prefer straight posts on my road bikes too, although this saddle is obviously not dialed in. 170's on this one.

I have a 33 inch inseam and ride 170, 172.5, and 175 cranks and spin like a gerbil on crack... The difference of 5 mm is really quite small and for average people this is a range that we can adjust to.

My mountain, touring, and one fg mountain bike have 175 cranks, road bikes are 170 or 172.5.

Maintaining spin off road is really crucial to maintain power to the back wheel, variations can cause stalls or spinning out on loose surfaces.

I ride a good number of fg bikes and find 165mm cranks to be a little short (longer femurs I guess) and am happy with 170 cranks and slightly narrower pedals or clipless to do increase cornering clearance.

I am not assuming a significant peak, and I suspect that there is a macho thing that says to use a larger crank. I am also assuming that there is a peak, that is all. Every person has an ideal fit of a bicycle for their physique. We have different seat heights and angles, different stem lengths, different frame sizes, yet somehow in all this all people can all use the same size crank?? That does not follow logically.

If you look at the crank, foot, and leg, there is lever action in each part. The most significant part of the lever mechanism is your leg, not the crank. For this reason the crank has less effect than your leg does, but to discount it entirely would be a mistake. I covered this already in a prior post.

The study only shows that with the lengths used, there is not much difference. It simply does not have the resolution to show that there isn't a peak in performance with a particular length- that would be an unscientific conclusion. It certainly does not disprove the French formula. I suspect that the people who did the study were not even aware that the French *had* a formula.

I agree that the improvement in rider performance is not going to be much, but why leave that on the table?

Since the title of this thread is cranksets, and since the OP's question is answered to his satisfaction, and while I have your attentions, here is a new question.

A crank designed for three rings puts the third ring farther out to the right than a crank designed for one or two rings: true or false? I put one of these cranks on my track bike. It has one ring in the position for the biggest ring, and he chain line is horrific. Putting on a real track crank should fix this, right?

Are the ring positions relatively standard for a given type of crank (single, double, triple)?

From my experiences I'd have to say a triple crankset places the inside ring even further in then a double does, this is just from my experiences experimenting with mounting different cranksets on different BB's on different bikes, I've run into the issue many times with a decent length BB on say a road bike using a triple crankset where the small ring section actually just ends up rubbing on the frame. This could just be coincidence, but it's my experiences.