Carbonfiberboy 

Here's a simpler way to think about crank length. Crank length is simply a gearing issue. We can use a standard "reductio" argument here. Given your current gearing, could you do that climb faster with 100mm cranks? No, you couldn't. You'd be hard pressed to just turn the cranks. Without a gearing change, it becomes a torque issue. If you can reduce the necessary torque with sufficient gearing, then any crank length will serve. Then it becomes a biomechanics problem, which is very difficult to solve because of the training issue. We become accustomed to a certain position, certain rpms, a certain crank circle, and only prolonged training with that new position, cadence, and crank circle can resolve whether or not it generates more power over a particular time span. This is not a simple problem. Hence the standard formula of: inseam in inches * 5.5 = crank length in mm. Most folks just use what came on the bike or else use the formula and see if that works for them. Or not.

Since your standard climbing cadence is considerably faster than 65, gearing your bike lower to allow a faster cadence and thus lower force would have been helpful. Just putting on shorter cranks doesn't mean you'll spin faster on a climb. To the contrary, because you can't spin faster unless you gear lower. One has to accept that cassette size is a visual for others which doesn't matter to you as you can't see it.

The climb from the Deli Stop to Sunrise is good training. I was at the ranger station a couple years ago, talking to a tandem team. They were about to start their 3rd repeat of the day. Can't say that tandems can't climb. An exceptional day ride is the clockwise loop from Ohanapecosh over Chinook and then White passes. People park in the equipment yard, to the left going in.

Iride01 

50/34 rings and a 11-28 rear? You might consider getting an 11-32 cassette or a crank with smaller rings. Or just ride 200 or more miles per week and you'll be able to handle that hill next time.

Wilmingtech

^^^^This.

Lemond1985

I go between 170's and 172.5's to 165's without issues. You should be fine, I doubt you will ever notice any difference after the first minute or so. I ride a different bike all the time, so my body is used to making small adjustments on the fly, so YMMV, but i think you will be fine.

I love my 165's because they allow me to use a powerful "kick forward" pedalling style. Often longer cranks create a weak spot at the very top of the pedal stroke, pretty much cancelling out any leverage advantage from the longer crank. The shorter crank helps me stay op top of the pedals through the whole pedal strike and use a "kicking" motion to propel me. I have a tendency to drop my heels a lot while climbing, and this helps quite a bit with that problem.

Clyde1820

I've noticed that as well. Shorter legs, here, and 160-165mm cranks have always felt "right," whereas typical 175mm's have that "weak" spot at the top you speak of. Haven't done 155mm's, but I suspect I'd do okay with those as well. 165's on the current bike (a rebuild, in progress).

Lemond1985

I think if you're out of the saddle climbing, crank length becomes almost irrelevant. For me it only matters when I'm seated, YMMV.

Carbonfiberboy 

My singles have 170mm cranks, our tandem 175. My stoker has much shorter legs than I. The tandem came with 170mm stoker cranks, but that long a crank made her legs cramp. The crank length on my singles is correct by the 5.5 * inseam in inches method. That same formula for my wife said she should have 150mm cranks, so I put those on for her last year. That totally screwed our seated climbing ability. She doesn't have the leg strength to get the power out of those shorter cranks at cadences which are powerful for me. OTOH her legs don't cramp and she's happier, so that's that. As I've said before, crank length is largely a gearing issue. Absolutely you'll need time to adapt your neuromuscular system to the longer cranks.

I assume "easier" means lower HR at the same power (speed). Yes, lower climbing cadence always reduces HR, but whether that's a good thing or not is another story. It's the same old story: lower cadence = increased leg stress and reduced aerobic stress. Perfect cadence and thus crank length, as the two are connected, is when breathing and leg stress are maxed at the same time. That's not a simple thing as both are modified by training.

Moisture

A 2.5MM difference in crank arm length is damn near going to make no difference. You'd notice more of a difference upgrading to a higher quality, lighter crankset or even changing out your gearing.

Crank arms need to be proportionate to your inseam and how much power you output.

phughes

The cranks I went to are 170, not 172.5. I wrote that by mistake. Even with a 2.5mm difference, you are changing more than the length of the crank, you are changing the circumference of the circle the pedals travel. You also have a 5mm difference total top to bottom.

Leg length alone isn't all that matters. A shorter crank also helps decrease the total bend of the knee at the top of the stroke, which can help people with limited flexibility due to injury, or other issues. It also helps put less stress on the knees.

I will edit my original response to correct the length.

Iride01 

IMO, The only thing that proportional sizing tells you is what the max length of crank is you should consider. Nothing about it shows that you must use that length.

And since your upper leg and lower leg aren't proportional on every person as well as your foot length, then saying one crank size for one leg length is border line silly.

Steve Hogg talks about crank length in detail, and while he somewhat supports proportional sizing, I like the considerations that he describes for different leg and femur lengths as well as other considerations. https://www.stevehoggbikefitting.com...gth-which-one/

All I can really say is like many other things, you can assume the accepted rules are the truth and never try anything different so you'll never know anything different. Or you can try different things and see what they do for you. I've found that sometimes the rules work for me. Sometimes, as in crank length, the rules don't work for me.

Moisture

For somebody with longer legs who is able to crank out proportionally more power, you'll definetely be better off with longer cranks. It ultimately means more power to the cranks.

I also used 175mm cranks before switching to a 170mm set due to worn chainrings. Didnt feel too much of a difference pedaling in the saddle, but still noticeable. Out of the saddle, going up a hill, the 5mm difference was certainly enough to limit my power output. I need to play around with the gearing more often on pavement to find the right pedalling cadence. I feel like I am constantly spinning at too high of a cadence and must compensate with a higher gear. On my road bike - also with 170mm cranks, its not nearly as bad because the gearing is better suited to my needs. I have a 34.5 inch inseam which means I need roughly 187.5mm cranks. I definetely felt like i was able to put down power alot easier the one time I tried riding with 180mm cranks.

In short, choosing a crank arm length in close accordance with your inseam is rather important, especially with shorter guys because it definetely can cause knee and flexibility issues like you said if the arms are a bit too long. However most frames won't fit much more than 175mm without pedal striking around the turns.

CargoDane

I usually use 172.5mm cranks, but with my newest bike (the only bike I have bought after my amputation). I ordered some 170mm cranks to see if it would help me spin better (with the proshetic foot, I can't use the foot itself to make a more "suspended" or "floated" revolution, if that makes sense). I can't really tell much of a difference in general, but I do find it slightly easier to spin, although I will never become a good spinner - I tend to mash. I think that at some point, I may try a slightly shorter crank still, just to see if it makes more of a difference for spinning.

Iride01 

I don't see crank arm length important enough to take priority over other concerns. If a person isn't having any knee issues or any other fit issues, why bother?

For persons that compete, whether with themselves or others, it might be something else they can tweak to find out what gives them the better power output. However I'd expect that power output when compared to their use of short and long to have mixed results with one better for some things and the other better for others. Constant rolling terrain, flat, long climbs at moderate grades, long climbs at steep grades, short 30 mile rides or longer 75 mile rides and other things will put one with an advantage for a unique set of circumstances.

I only know that for my 34.5 legs, I prefer 165 mm. 175 mm cranks that I tried out for 10 miles wore me out on a 58 cm frame. Getting on a 56 cm version of the same frame with 172.5 cranks immediately after getting back to the shop and going the same 10 miles let me feel more rested and actually produce better times for specific segments in that ride and overall times. I'd rode my own bike five miles prior to the test rides, so I feel I was decently warmed up for the first ride.

I'm not saying my choice for short cranks is the right choice for everyone. I'm just saying it's my choice. Not some formula that I'm not supposed to question and blindly accept.

Lemond1985

Good points. I read all the articles back in the late 80's and early 90's about how all the pros used 175 mm (or longer) cranks. The conventional wisdom at the time was that longer cranks were always better. Reminds me a little bit of the "wider tires are always faster" fad we are currently in the midst of.

Anyway, i struggled for years trying to get 175's to work (I'm 5-10) and I got nothing but low back pain, which I would recover from, but would always come back. I kept trying to fix the flat spot at the very top of the pedal stroke, but my knee was always too bent to apply much power. Fighting it only caused more pain and injury. These days, I find 165's and 170's much more to my liking.

Road bikes were sold for decades with gearing way too high to be practical (a 42 x 23 low gear???) for the average person, but that is finally changing. I think the idea of routinely putting 175 or 170 mm cranks on every bike sold also needs to be re-examined.

Leisesturm

OMG. What a mess of good information, misinformation, myths, lies, talking over each other ... here, I'll add some more of my own, why not. I skipped a lot of posts after #19, but #26 stood out for being rational and accurate. What I didn't see (but may have missed) is the observation that, were it possible, most of the bikes we ride would have cranks of 200mm!! The reason why it is not possible is because the average bottom bracket height is 10.5" and longer cranks than the current standards might contact the ground during a turn. If you are racing. Most of us aren't. The cranksets on the bikes we ride are however derived from the TdF racers of the 1960's. When all cranks should be 200mm, it becomes a little strange to obsess about the difference in anything between 170mm and 172.5mm cranks! I've been riding a new bike with 175mm cranks and didn't know it because the specs on it say 170mm. I've got the cranks on the workbench though because I pulled them to install a mid-drive e-assist and 175mm is plainly stamped into the aluminum.

I also ride recumbents and on recumbent forums this topic gets quite a bit of attention. I didn't expect to see it here too. On a recumbent there are any number of reasons why a shorter crank might be neccessary. Shorter meaning 155mm ... 150mm. Even 140mm. Reductions on that order of magnituded are perceptivle in their effects on things but IMO the main reason on a recumbent to do this is because it is enclosed in some kind of shell that restricts the circle diameter of the riders feet. Knee issues should be addressed in their own right. Bicycles are transportation, recreation and/or sport. IMO they should not be used as physical therapy devices.

There is all that, but there is also this: 2mm is quite possibly the manufacturing tolerance of a cheap (affordable) crankset. One or both arms of a 170mm crankset could easily be as close to a 172.5 as matters and thus pulling the first set off to install the second (or vice versa), especially if money was spent acquiring the second... ... TL;DR: go big or go home. If you are going to change crank length for some reason, nothing less than a 15mm change is worth the time, money, or hassle. And, cranks LONGER than 170mm - 175mm have their place. For taller riders, sure, but average height ones as well.

tomato coupe

No.

Carbonfiberboy 

That's a snippet from a comment. Further in that comment, I explained that pedal force would have to increase on a climb if one went to shorter cranks without a gearing change and wanted to maintain the same power. Do you disagree with that? Yes, no?

tomato coupe

Agree.

Wilmingtech

Mentioning Cranks on BF is like mentioning oil on any number of automobile forums.

Anyways I was listening to this Podcast from Trainer Road "Ask a Cycling Coach" Episode 287 and starting @ 01:36:00 They have a great discussion with quite a few examples and research on crank length -
Here is the excerpt from that episode -
Overall it seems that you will be better off with shorter cranks than long ones. Most of the reasoning seems to be around the ability to have a faster cadence with shorter cranks with less effort.

-Sean

rydabent

IMO as a somewhat taller person, the longer crank arms should work well for you. If you can handle longer crank arms, logic dictates you can apply greater torque with the proper gearing.

Wilmingtech

It has been over a year now and I wanted to follow up on this post. I have made quite a few changes to the bike that was initially mentioned that I switched out to the shorter cranks.


Changes made to the bike -

Ridley Helium:

2020 - 175mm cranks, 11-28 Cassette, SMP Avant Saddle

2021 - 170mm cranks, 11-30 Cassette, Specialized Power Saddle


My build and strength is more of a sprinter than a climber. I weigh in at around 180lbs (175 when in good shape and 185 when I am taking extra helpings of dinner and dessert) and I have a pretty good sprint (1100w for 15 sec) for my age (50) considering I only put in about 3000 miles a year and don't race or train other than for personal improvement and friendly competition against the other guys that I regularly ride with and improving my Strava segment times.

Most of the riding I do where I live is more Ardennes style short punchy 1-3 mile climbs with lots of rollers. But we are surrounded by mountains and there are a few rides that do have climbs in the 10+ mile range. In 2020 the notable climbs were the ride up to Johnston Ridge on the Spirit Lake Hwy (504 up to Mt. St. Helens) and then we have a loop that we do a couple times a year from Ashford, Wa up to Paradise (Mt. Rainier) and then around to Packwood and back to Ashford on Skate Creek Rd.


Here are the Profiles for those 2 rides to give you an idea -


These routes are quite different from the short punchy climbs and as such I figured I would try swapping to the shorter cranks for the long climbs to see what kind of difference it would make and how it would affect my rides.

One thing to note is that I was in much better cycling shape in 2021 than I was through 2020.

The difference between the 175mm cranks and 170mm cranks is quite noticeable. The 170mm cranks feel like a department store bike with the shorter turns and after using the 175s for a while I feel like I am spinning at a higher cadence to keep the same power in the same gear. This is not a bad thing it's just a different feel for the shorter cranks. I do notice I naturally ride in a slightly higher cadence in the shorter cranks (slightly above 90rpm vs 85-90 on average). I do not feel like I can kick up a sprint on the shorter cranks like I can on the 175s. For the same cadence (I can spin the 175s up as fast as I can the 170s) there is more power output on the 175s.

Where I did notice the difference when switching to the 170s is that on these long hauls I was able to keep a more consistent power output over the length of the climbs. Unscientifically (as I have not done these climbs twice on the same day with the same bike with different cranks) I noticed that I was able to push closer to 220w and keep it there much later in the climb on the 170s where as the 175s I would keep up with the guys in the bottom half of the climb but as it got later into the climb I would start to fall off and struggle to keep up with them.

Don't get me wrong the 170's didn't allow me to stay with the guys on the climb the entire way (As I climb like a sprinter) but they did allow me to hang a bit longer with them feeling less leg fatigue than on previous rides up these climbs.

One other thing that was overwhelmingly welcome with the 170's is that I did not get the leg cramps going over the top of the Paradise climb. The previous 3 times I have done this route I would always cramp up toward the top and have to shovel bananas and quite a bit of electrolytes to manage as well as stopping to stretch a bit at the top of the climb and even then would still feel some cramping start to creep back up on the descent and later into the second climb as well. Some of this may be that I was in better shape for the climb this time around but I also noticed strain on different muscles as well.

The Sartorius and Vastus Medialis (Inside of my thigh) were where the noticeable leg cramps were on previous climbs on the 175's where as this time I felt a little more strain on the Vastus Lateralis and Rectus Femoris (Top and outside of my thigh) than in past climbs. This may have been due to a bit of seat adjustment when I swapped out the cranks. With the shorter cranks being, well, shorter, the bottom of the pedal stroke is slightly higher from the ground and the spindle on the pedal is now closer to the bottom bracket. Taking these adjustments into consideration, I pushed the seat up a 1/2cm and also revisited the KOPS and adjusted the seat back when I went to the Specialized Power Saddle. I do think there is a better average over the muscle groups now with the shorter cranks.

I do have a 2nd bike that I built over the winter (Another Ridley - Noah SL) that is more for my regular rides with 172.5 cranks. This bike is more aero and fun to sprint and descend on. The Helium project over the winter this coming year will be to see if I can shed more weight from it and keep it as my all day climbing bike. Its already pretty light weighing in at around 7kg but I am certain I can find a few more grams to drop.

-Sean


PS - Some gratuitous pics from the Paradise ride this past week

scottfsmith

Thanks for the update!

I also made the 175 -> 170 switch about six months go based on a bike fitter recommendation. I confess I paid no attention to it after the first 5 minutes on the new cranks.

But, in looking at my cadence numbers I have gone from 80-85 to 90 on average. It took awhile to get there but my body slowly adapted to the new cranks. I'm standing less as well, not sure why but less force in the seated cadence means I don't need so much relief perhaps.

Crang

Im 5'7" but with a short 28" inseam. I recently moved down to 165mm cranks and got quite a bit of relief in my old knees. I see everyone here posting height but not inseam- seems like thats what matters. My torso is a couple inches too tall or legs are too short for my height.

Clyde1820

Am 5'9" but with the same essential dimensions. Long-waisted, and shorter legs. Add to that an old injury in one leg/hip, power's down significantly there, and so I find 160-165mm cranks much more tolerable. I've altered the gearing way down from typical, to accommodate. Works best with the shorter cranks. Might not work for everyone, but it seems to work for you (knee joint relief) and me (easier pedaling, better cadence, more tolerant of injury area).

Carbonfiberboy 

My wife has a 27" inseam and rides 151mm cranks. In the universe where we all ride cranks according to leg length, you'd be on 155mm.