I switched to 165s on my commuter and it helped with my knee pain. Knee pain that originated when I tried to "train" myself to spin faster than normal on 172.5s. A few rides like that and I had knee pain linger for six months after! I'd really made a mess of myself.

For me it was the same way, very noticeable, but then you've got to raise the saddle a comparable amount so your foot ends up the same distance from you at the bottom of the stroke. At least that's what I did when I switched to 165s. That way your knee and hip aren't bent as much at the top of the stroke. In my experience that's what hurts them. But as you say, different people are indeed different.

I'm 6'2" tall but I'm extremely flexible, and I'm pretty sure my knees are dislocating slightly when they bend so much at the top of the stroke on longer cranks. Decreasing the movement, both by decreasing the cadence and decreasing the joint angle by decreasing the crank length and raising the saddle, works well for me. That in addition to a weight-training regimen to stabilize my knees.

I watched the video. Interesting. The presenter does mix up leverage, cadence, circumference, force, etc... a bit. And the conclusion was pure speculative theory.

Different people have different preferences.

I've started purchasing 180 cranks for my bikes (with me at 5'10). Except for my TT & Funny bikes which I go with 175.

I'm a masher, and am happy with the slower cadences. Although, that has been evolving over time. I've also been reasonably flexible, so I like the longer range of motion I get with the longer cranks.

I'm a commuter that will on occasion do longer rides, but not a racer.

Other people like shorter cranks, even down to 165 or so for one reason or another.

Longer length gives one more leverage, but also a longer crank circle, both varying linearly with the crank length, so the power/effort remains essentially the same, and is easily adjusted using gearing.

Now, I mentioned 180's on the road bike, but 175's on the Funny bike and the TT (which I still have to finish building up).

There is actually a reason for the discrepency.

Lengthening the cranks by say 1cm (170 to 180), means lowering the seat by 1cm so you can reach the pedals at the bottom of the stroke, and the knees come up the equivalent of 2cm higher. an one runs into the risk of knees to gut.

For bikes with very low bars, one is forced to do various adjustments to increase the body/knee angle including pushing the seat forward, and using shorter cranks.

At 6’3” I prefer 175s, but most mid-level bikes were shipped with 170s, so I make do with what’s there.

I once had only two bikes: Both road bikes: One with 170 and one with 175 cranks. I noticed that it felt more smoothly professional to pedal the 170s after the switch from the 175s. When I switched back to the 175s, it felt slow. Slow is hard to do smoothly or professionally but in my head, I'm thinking about having more "leverage" which is good (right?). Then, we had a guest instructor at a club clinic one day who was my size and he prefers 172.5s. So that is my go-to these days. I'm still slow, but smooth, and not professional.

Tandem riders will sometimes adjust the impression of cadence using the crank length. So, if say the captain generally spins faster than the stoker, give the captain long cranks, and the stoker short cranks, and the two will feel more comfortable pedalling together.

When people talked about crank length, I found it silly to think that people can feel the difference in 5mm. Then I was riding a new-to-me bike, and I couldn't get the seat height right. I kept raising it and lowering it. Then I realized the cranks were 175. What a difference. And the difference is really double, because a 5mm difference in radius is a 10mm difference in diameter. And then there is all the trigonometry of our knee angles etc, so it really does make a difference. I've tried shorter cranks, and they feel a little funny but not uncomfortable. Once, a friend loaned me his bike for a day ride we took together. It felt a little off, so I checked, and yup, 172.5 cranks. They weren't so long as to annoy, but I do not like 175.
[MENTION=73614]rhm[/MENTION] once saw a "junior" crankset on ebay in France, and he suggested I buy it. It had 155 cranks. Later, he confessed he was hoping I would dislike it so I could pass them to him. Well, I like them. I have them on my street fixie. It's geared low, so being able to spin fast helps. I had to raise the saddle, of course, but that's OK. I loaned that bike to a nurse visiting NYC for the pandemic. The nurse said they'll return it, but I know I might never see it again. We will see.

My speed breakthrough came when I went from 170 to 175 40 years ago. Used it exclusively since except: my old Peugeot fix gear; no ground clearance, a newer Peugeot fix gear; same issue and an '80s race bike I set up as a double with 172.5s. Knees did not like that bike! I now keep the Q-factors down, ride only 175s and only triples and fix gears.

170 works well for me, 175 is fine too, and I have put down some real power/speed with 165mm cranks. I do modify my cadence slightly depending on crank length, but I don't think it matters too much. I'm 5'11" with a kind of short inseam for what its worth. I think the best for me is 170, or maybe 172.5, but I don't care much either way.

I used to be in the "doesn't matter, don't care" camp. I'm 5'11", 33" inseam, and had bikes with 170, 172.5 and 175 cranks. They all seemed okay to me.

Until a year or so ago, while recovering from being hit by a car. No impact to my knees, but the other stuff affected my overall posture and eventually filtered down to my knees.

Now the bike with 175 cranks demands careful saddle height adjustment. If it's too low I'll get knee pain from pressure at the top of each stroke; too high, and I get lower back/hip pain from rocking in the saddle. I don't feel any sense of leverage and still tend to spin rather than mash on that bike.

So I mostly stick with 170 or 172.5 cranks. The only time I noticed any difference was when I switched a set of 52/42 Biopace rings from the 170 to 172.5 cranks. Within a few rides using the slightly longer cranks I had knee twinges. My cadence felt herky jerky. Switching back to the 170 cranks solved that problem. But with conventional round rings I don't really notice any difference between 170 and 172.5.

Some day I'm gonna try some 165 cranks, if I can find the right frame project. I have a feeling it'll be easier on my knees about 10 years from now.

The Brits had this figured out many decades ago. The amount of flex in the knee at the top of the pedal stroke increases with longer cranks, thus causing an overall decrease in performance. There is a certain amount of flex in the knee that's considered ideal, and that's what people should be shooting for when choosing a crank length. I'm 5-10 and love 170's and 165's. Used to ride 175's for many years, and had a lot of pain, along with no performance increase that I could notice.


https://cimg7.ibsrv.net/gimg/bikefor...b5111b6ab6.png

https://www.bikeforums.net/classic-v...l#post21465205

All good stuff in this post. Everyone's physical geometry is different, and therefore crank-length choice becomes personal, much like saddle choice. I've ridden everything from 175 to 165, and I've written it all off as to what is suitable for a particular bike at that point in time. I also want to compliment you on your loaning of a bike to a visiting nurse. You've got a good soul, Tom. Thank you for helping support the front-liners! :cheers:

I went ahead and switched it to 170’s. Lots of great info everyone shared, as always. I‘m a spinner, I stick to a cadence for the entire ride. Habit I picked up racing triathlon and using cadence sensors. I was most worried about knee pain which was brought up a lot. As of now I don’t have any knee pain and I want to keep it that way as I get older. Thanks again to a great bunch of people.

You could still try the 175s and see what you think. Some people do fine with long cranks.

I found 175 is my strongly preferred to the point that my vintage bikes that have 170 on them get ridden much less. I am 6' 2" and have been to a bike fitter that uses Retul and confirmed that 175 is best. Of course smaller does not hurt, it just feels so much less power / leverage when pushing and especially climbing.

My challenge has been when I get a vintage bike I really like the search for 175 cranks has been costly to replace the 170s, especially on French cranks. I have mixed feelings but have used Velo Orange on one bike, but it is not a bike that I am concerned being a purist.

I’m 68 and “now” 5’8” with 29” inseam. I rode 170mm for decades on my road bike. When I started mountain biking I rode 175mm.

About 5 years ago, I found an NOS Ultegra 6503 crankset with BB for less than $150. It was 172.5mm. Now I ride 172.5mm on my road bike and haven’t noticed any difference.

John

I have 170mm on two road bikes, 175 on a road bike, 172.5 on a gravel bike, and 180 on a touring bike.

The 180s are fine, don't love em or hate em...i think they feel different but can't tell if it's me wanting them to feel different or actually feel different.

In theory, the 180s would be great since in 6'5. I really dont care either way though.

148mm?? No wonder you had no power! Those would fit someone a foot shorter. You'd probably do great on 160's, but they're very difficult to find, so your 165's sound good.

(148. Golly.)

Here you go!

https://cimg6.ibsrv.net/gimg/bikefor...af95f8d78f.png
Rennen Adjustable Crank

I actually saw one of the above in the wild back in January.

See also:
https://cimg5.ibsrv.net/gimg/bikefor...e4197c1ae.jpeg
Helium Dos 2 Size Cranks 120/125 and 130/135mm

Seriously, though, two years ago I replaced the 170s on my early 80s Merckx with a Velo Orange 50.4 BCD in 175mm because my guy at the LBS suggested I might like 175s better and because the 170s were out of stock at VO at the time. They felt weird at first.

A few weeks later I picked up a long-tail cargo bike with 175mm and a few days after that, a friend gave me a BMX race bike with 180s. That put things in perspective. I fell in love with the later, though not with the crank length. I am now happy with 175s on all three bikes, so neither of the other bikes will mess up my BMX spin.

You’ll get used to whatever you use, within a reasonable range. So long as you can adjust your gearing accordingly and you’re not scraping pedals if you pedal while cornering.

Crank length experiments are covered in DeLong's guide to Bicycles and Bicycling. They were found to be the least critical dimension in fitting a rider. The longer cranks just get turned slower, and can be hard on knees, while the shorter ones get turned faster, and tax our dexterity.

180mm's
 

I reasoned that I should have longer cranks, based on my height compared to "average." I'm 6'-2" and the average cyclist is 5'-8", or whatever, so by simple proportions I decided to try 180's. They are scarce. I put 180's on both my road and time trial bikes. I rode and raced on 180's for several years. I still had 175's on other bikes.
The left 180 crank arm broke on the road bike (causing permanent injury, by the way) and then I sold off the TT bike.
Going back to 175's I could not tell the difference.

Exactly; too-long cranks are hard on my already arthritic knees.

The first time I tried 165's on my road bike (I'm 5-10) my first reaction was not great. "I'm riding a little kid's bike!" is how it felt. But I got used to them and I found it was a lot less work to get the pedals around than with 175's. Slightly less leverage, as the person above noted, but overall, less tiring on the body, and less taxing on the knees and hips.

Shorter cranks tend to make me want to spin more. But 175's always gave me knee, hip, and lower back pain. Nothing that didn't heal up eventually, but why deal with it if you don't have to? Glad I ditched those. 172.5's are OK for short rides, but I mostly prefer 165's and 170's these days.

I've had some back problems, that were mostly taken away with consistent ab workouts. But to help even further and prepare for a coast to coast race, I decided to get a bike fit. The fitter noticed that my hips were rocking a little too much and recommended a shorter crank. I'm not the tallest at 5'9" and according to him, the crank length I had was probably too long anyway. I settled on 165's and the rocking lessened. He also cited various articles and research that concluded shortening the crank did not decrease performance. After almost 2 years since the change, I am happy with the results.

Speaking of arthritis and knees (I know this thread addresses more performance)....my 4 bikes focus on keeping knees flexible and maximum range of motion at 71 years old, 6'4 and long inseam. I do 4 short rides a day. Start with lower handlebars and 165 cranks....then higher position and 170, then higher and 175 and finally cruiser position and 180 cranks. Gradually increases range of motion throughout the day. I cobbled together a 195mm set (fabricated from 2 cranksets) but had knee pain with these. Actually, would like to try these again with more conditioning and reduced knee stiffness (with diet, weight loss and supplements to reduce inflammation).