am8117

I have tried to delve into the (not-always-so) scientific articles on the web about this, but looking at my own history after having changed crankarms from 172.5 to 170 I felt no difference ...

Could anyone tell any difference going marginally larger crankarms, eg. 172.5 to 175? I thought staying on the shorter side of the sweet medium was always safer, but wonder if there's actual real world experiences in this small steps (of 2.5mm)?

PeteHski

It probably depends how marginal your range of leg motion was in the first place. I can go from 172.5 to 175 (and regularly do) without noticing any difference whatsoever. But I'm quite tall (184 cm) with long legs (88 cm true inseam).

tempocyclist

My two road bikes are both 170mm. I noticed no difference when I rented a bike for a week and it had 172.5mm cranks (saddle height adjusted accordingly). Some people may be more sensitive to change.

Iride01 

And on the flip side of that, I'm 180 cm tall with 87.6 cm inseam and ride 165mm cranks. When I've made an effort to try longer I just don't like them as for me they wear me out because I feel like my legs are thrashing too much.

I tend to think that for people that only like a slow cadence, they'll do better on longer cranks. Those that can handle faster cadences into the 110 to 120 or better range might like shorter cranks, but its not a given. It's something a person has to try and see for themselves. There'll be fit changes that will need to be addressed when you change to longer or shorter.

Rolla

I've ridden every size between 165mm (fixed gear) and 180mm (BMX), with my road, mountain, and gravel bikes at 172.5 or 175mm. For me, it's mostly about pedal strike when cornering on fixed gear or hitting rocks, logs, and ledges while mountain biking. But unless I'm at the two extreme ends, I don't notice any difference in my cadence, leverage, or leg speed. If they didn't mark the sizes, I'd never know which I was riding.

whatshubdoc

I think it depends on your personal sensitivity (princess and the pea-ness).

I started road biking 20+ years ago on 172.5mm cranks not knowing what to buy for my leg length. Rode that groupset for 10 years. Now I only ride 172.5 after trying 170 and 175 for 6 months each.

My mtb rocks 170 cranks as they do not make 172.5 for MTB but I can tell. And some days it bothers me (long spin/climb days mostly) but others it doesn’t.

urbanknight

A long time ago, I was told that longer cranks aided in climbing while shorter cranks were good for spinning higher cadences, and also for clearance on fixed gear bikes (velodrome banking or cornering). No idea how valid that is, but it made sense to me and I ran a 167.5 track crank, 172.5 or 175 road crank, and 177.5 or 180 mtb crank. As long as I set the knee cap over the pedal spindle, the crank length didn't seem to matter with regard to fit. As far as performance, I barely noticed the difference in feel between all of those cranks, so no clue how much it helped or hindered my performance, if at all.

Germany_chris

I have short legs but prefer longer cranks, I like 175/177 on my road bikes and 180 on my mountain bikes

Troul 

if i was given a choice, 177.5 would be on my Domane. I have not looked to see if that exists, but it is the preferred length that I do best with.

I've used the other various lengths on other various frame, & i just was more satisfied with the 177.5.

subgrade

I've tried 170 and 175 mm cranks, and the difference, while not crucial, was noticeable. It didn't affect my speed or knee condition, but shorter cranks are inducive of slightly higher cadences, hence lower gear at the same speed. Being more of a masher, I think I slightly prefer the longer cranks.
P.S. I'm 185 cm (6'1) tall with 89 cm (35 in) inseam.

jgwilliams

I think you'd have to make a bigger change to notice it. I used to run shorter cranks (165, I think) on a recumbent and felt it made a definite improvement. On my road bikes I always seem to have ended up with 172.5 and been quite happy with it.

Like you, I read a number of articles on it. It would seem that the crank length doesn't actually make a great deal of difference to the power output as riders tend to use a higher cadence on shorter cranks. I think it's largely down to personal preference. Don't forget, though, that you need to compensate by adjusting the saddle height, Possibly not for a mere 2.5mm, but I'd have thought once the change is up to 5mm you'd probably start to notice.

PeteHski

Longer cranks for climbing at low cadence? Maybe if it doesn't cause issues with your range of leg articulation. Shorter cranks for spinning? Certainly makes it slightly easier to spin if that's your goal. Performance? Well that's coming from the rider, not the crank length. As for KOPS....... well not much credibility in that concept today.

From reading all the literature on crank length, the only thing that seems to be an issue is if you go too long and start getting injuries from too much knee/hip joint articulation. So if in doubt it's best to run shorter cranks. The other thing that comes out is that most bike manufacturers fit standard cranks that are too long for short riders.

DaveSSS 

There's a theory that crank arms that are 21.6% of cycling inseam. I'm only 168cm tall, but my cycling inseam is 83cm, so I decided to try 175mm last season and they're working out fine. I did lower my saddle about 3mm. By this theory, the really long legged riders need a lot longer crankarms than 175. I never use KOP to set my saddle position. I'm significantly further back. I made no change to setback when I moved from 170 to 175.

https://zinncycles.com/custom-cranks/

PeteHski

Where does the 21.6% come from? Theories are great if they are both explained and proven in the real world. Where is the research, proof etc? I can't see on their website. Maybe I missed it?

easyupbug 

In my experience between 170 and 175 the change is just like a gear change. My longer crank just gives a little bit easier gear and a shorter crank a little bit higher so shifting gears adjusts that. There are other reasons varying from knee and back issues to riding triathlons that deserve further study.

Kapusta

I have seen the article it is based on, though I don't remember where.

It's certainly less random than whatever bike companies use to decide what crank length to spec on their bikes.

urbanknight

Yeah, I know KOPS is considered useless today, and I actually get better power to the pedals with the seat further forward, but I get knee problems.

Good point on the short rider thing. I've never seen anything shorter than 170mm on a road bike, even a 48cm for people under 5'.

PeteHski

You would think they would mention it on their website, but I can't see it. Other studies I have seen don't tend to agree with this theory. According to this I should be ordering custom 190 mm cranks. No thanks.

PeteHski

If you are interested, this is the best 1-page impartial summary I've found on crank length.

https://bikedynamics.co.uk/FitGuidecranks.htm

70sSanO

This was basically what I was taught. I rode 170’s on the road for years and when I started mtb, I just adjusted to the 175mm length.

I used monetary analysis when I swapped out my road cranks with an NOS 172.5 at a good price.

I do feel shorter cranks are easier to spin.

As for KOPS, I’ve used over the knee over pedal or slightly back (mtb) for decades. It has served me well, and at 70 and fortunately without knee pain I don’t have much reason for change.

John

bargainguy

I'm 5'4, and have a keen interest in folding bikes as well as road bikes. Had always ridden 165mm or 170mm, never greater than 170mm.

About 15 years ago, I decided to experiment with short cranks on my folders. I had Mark Stonich of BikeSmith Design and Fabrication shorten a couple 170mm Shimano cranks for me, an Ultegra triple and a 105 double. He shortened both by 22mm (the standard shortening capability of his basement CNC setup) to 148mm, drilled and tapped new pedal threads, and rounded and buffed the new crankarm edges.

What I found was interesting. Much easier to spin, but at the cost of seemingly reduced power. Really felt it going up hills and against a strong wind, like I just couldn't get a decent power stroke going. It was easier to pack either one in a suitcase for travel with the shortened arms, however.

While the easier packing was a plus, I couldn't handle the reduced power, so I went back to 165mm and 170mm on the folders about a decade ago. Still have both short cranks in case I find a special project for them someday.

Kapusta

Have you actually tried 180-190mm cranks for any length of time?

I don’t know whether that ratio is correct or not. What I do know is that we all tend to get used to whatever we are riding, whether is is optimum or not, and changes from that feel weird at first.

The reason everyone is so used to 170-175mm cranks is because that is what most bikes come with.

Kapusta

Regarding MTB crank length: for years the conventional wisdom was to go longer than road, and 175 was pretty much the standard for average folks. But recently, that is starting to change and cranks are getting shorter. At first this was due to the lower bottom brackets leading to pedal strikes, but as people try it, many seems to really like it. The MTB I just bough comes with 165mm cranks for the med and large sizes.

urbanknight

I think that plays into that earlier comment about crank length being like a gear. You shortened the lever, so it's going to require more force from you to move it at a certain speed. Of course, you can only go down so many gears and spin so fast.

PeteHski

No, I've only tried shorter cranks and found them to be fine. Most of my riding is endurance based and my legs are 54 years old. So I appreciate a bit less joint articulation while pedalling, especially 6 or 7 hours into a big effort. I would need to see some hard evidence clearly showing 190 mm cranks are optimum for me to even think about trying a set. Everything I've read recently suggests that standard cranks (172.5/175 for me) are in the ballpark for my inseam and going shorter (165-170) might actually be beneficial for endurance (even less challenging for my ageing joints).

The only advantage I can think of with longer cranks is for very low cadence climbing if you run out of low enough gears. Which used to be much more of an issue before wide-range cassettes and compact chainsets became available.