The short crank trend

[nathanong87]

https://www.youtube.com/watch?v=Vl3xgFw-u8A

From 177.5 , wiggins now uses the 170mm because of the track team being 'asked' (forced) to use shorter cranks and probably wants to use them for familiarity.

[allencanna]

I am using from 170 to 165,and now 150.
there are someone in America who shorten the arms professionally.

[racersir]

Im quite intrigued by this short cranks. I'm 182 cm tall bb to saddle height 79cm went from 172.5 to 170 can't really tell the difference. I just bought 165mm cranks to try out. I'm hoping it doesn't feel to weird the 165.

[TheKaiser]

I am in the process of running a trial on some 165s dropping from my usual 175s, although my primary interest is reducing knee discomfort, not increasing wattage/dropping drag, although that would be a nice bonus.

[11.4]

I was chatting offline with someone on this forum, having an interesting discussion about crank length. A few thoughts came to mind that I thought I'd post here. Thoughts?

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Everyone thinks that crank length should relate to leg length, but that's fallacious. It's more about the appropriate circle that the foot can rotate, given hip impingement, hip rotation, interference between chest and thigh, how far forward one is sitting, choice of saddle, hip tendon inflammation and restrictions, amount of tension in the ITB, amount of heel flexion that a particular rider can support effectively, and on and on. Not one of these, you'll notice, has to do with leg length but all will limit (or enhance the effective range that the pedal can travel.

Actually, travel ... and still deliver power. Which is another non-leg-length issue. It's interesting to see how a rider can deliver significantly different power with one crank length versus another in some instances. A lot of riders will use longer crank arms than they should because they believe they are gaining leverage, but they aren't actually creating much power in some instances, creating ferocious power in others. The same is true of shorter cranks -- a rider who can deliver, say, 135 degrees of rotation at wattage over X will be a better rider than one who can deliver wattage of 1.3X but only over 70 degrees of rotation. Most of the leg length to crank length studies have failed to take some of these issues into account, typically by measuring only short arc power or another fallacy.

So I don't really go much for the whole leg length measurement thing. It's rather bogus. You could easily do better and feel better at 170 mm, but it'll be for all the other reasons I mention above, not because you have a 38 inch inseam. Make sense? Same thing affects frame sizing and is an issue that many frame builders and frankly most fitters don't think to address.
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[KWalker]

I do not have flexibility or impingement issues, but my fitter (who fits many on the WT level) decided to try 170s with me (from 175s) just to see if it helped my right side come over the top of the stroke with more consistent pedal pressure. I have a LLD on that side AND, for whatever reason, on 175s I would momentarily release tension only for it to spike when tension re-engaged on the downstroke. Also, since that side is shimmed, at 3 o clock I had a bit too much heel drop with 175.

Switching to 170 helped quite a bit in eliminating that problem. Doing brake ergometer tests I was able to apply more force from 11 to 1 o clock, which was the problem spot.

Only 2 rides on them so far and it was strange for about 30 minutes, but I did notice the increased cadence quite a bit. Moreso was the ability to accelerate or "snap" the gear just by turning the legs.

I have been on 175s for most of my riding aside from 2 years where my SRM was 172.5. No idea why I went back to 175, but one interesting thing I noticed was that my out of the saddle lower back/core is much more engaged, aligned and stable. Smoother stroke especially while sprinting.

Adjusted saddle 5mm upwards and 1.5mm forwards. We found that for whatever reason the switch made my dynamic knee over spindle orientation further behind the pedal and while this is just a rough metric, on the road it felt as it forward made sense.

[TheKaiser]

Everyone thinks that crank length should relate to leg length, but that's fallacious. It's more about the appropriate circle that the foot can rotate, given hip impingement, hip rotation, interference between chest and thigh, how far forward one is sitting, choice of saddle, hip tendon inflammation and restrictions, amount of tension in the ITB, amount of heel flexion that a particular rider can support effectively, and on and on. Not one of these, you'll notice, has to do with leg length but all will limit (or enhance the effective range that the pedal can travel.

You could easily do better and feel better at 170 mm, but it'll be for all the other reasons I mention above, not because you have a 38 inch inseam. Make sense? Same thing affects frame sizing and is an issue that many frame builders and frankly most fitters don't think to address.
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I agree with all of those statements. One of the challenges is that the list of factors at play that you listed is pretty huge and, as you point out, the list can go on and on even further. Not only that, but many of those factors are interrelated (for example, adjusting seat for/aft will tend to alter ankle flexion), and some may even be transient (like hip tendon inflammation).

That all is to say that is a messy thing to assess, and doesn't fit well into formula based fitting, as many of these things are difficult to quantify and are moving targets. Additionally, crank length is not generally adjustable with the same ease of low expense as saddles and handlebars. This all makes it hard to integrate into the sort of fitting format that many of the big name systems use.

Until someone solves the Unified Field Theory of Bicycle Fitting, one recommendation that I think may have some value came from Lennard Zinn (somewhat of a long crank advocate). Despite liking long cranks for taller people, he recognized that long cranks can compromise fluidity across the top of the pedal stroke due to excessive joint angles, and recommended the following simple method to see if they will work for you. All you need to do is lower your saddle an appropriate amount to simulate the joint angles that you would experience with a given increment longer crank. Observe if you feel any binding when the foot is coming over the top of the pedal stroke. If so, then longer cranks will mess with the fluidity of your pedal stroke. Of course, this only will work to test "fluidity" and check for binding, it won't allow you check power production as you will effectively been under extending in the 6'oclock position, but it is a kind of "functional" and easy test that will demonstrate your ability to manage the joint angles given the current collective of the factors that 11.4 mentioned.

Unfortunately, using that method in reverse to see if shorter cranks cause an improvement will be somewhat compromised by the excess extension on the opposing side, which will tend to cause the hips to start rocking.

For people looking to test going shorter, or who want to test power production with longer, I often suggest just buying a couple sets of the cheapest compatible cranks in 5mm increments either up/down from your current one, if you just want to experiment, or down/down if you want to truly see how much of a change would be optimal, and then doing some extended trials. You would of course want to check for fluidity improvements as KWalker mentioned in his comment, and then you could also check for power (assuming you have a pedal or hub based power meter). My personal opinion is that too many people "experiment" with a single tiny 2.5mm change and then pick their preferred of the 2 and call it done, when in reality the change is so small that it is likely that any effect is placebo related.

The truth of the matter is that you don't know you have the optimal option until you have gone too far and then return to the the one that is now conclusively best (for your current circumstances). If you are trying an up/down crank length trial, and you see that 5mm longer is worse, and 5mm shorter is better, then I think you owe it to yourself to try 10mm shorter too, to see if that is even better still.

[TheKaiser]

Adjusted saddle 5mm upwards and 1.5mm forwards. We found that for whatever reason the switch made my dynamic knee over spindle orientation further behind the pedal and while this is just a rough metric, on the road it felt as it forward made sense.

Was that 1.5mm forward measured relative to seatpost clamp or measured relative to the previous saddle to BB setback?

In other words, were you just compensating for the increased setback that raising the saddle caused due to the seat tube angle and preserving your for/aft position relative to BB, or are you actually more forward relative to the BB?

I hope that makes sense, it always seems excessively wordy to describe these things, but different fitters use different reference points so it pays to confirm.

P.S. Glad the shorter cranks are working out for you!

[KWalker]

I move the saddle 1.5mm forward in the clamp, which put it same over BB as before. At first intuition told me to put it back, but when we looked at me on the trainer I was able to rotate my pelvis just a slight bit more, which pulled my knee back over spindle more than it was before. Fitter gave me guidelines to try both forward and back on the road if I felt I needed to and trying forward seemed to feel the most natural. He isn't firmly devoted to either static or dynamic KOPS, but rather how changes in that influence foot movement over the pedal stroke. For me personally if things are too far back my heel drop becomes too severe and I almost pedal from "behind the stroke" rather than on top of it.

[Kojie]

Cobb sells short cranks which isn't expensive. I am using 155mm which I bought from rotorusa cost is around 330$ the 3d24 models

[mulletmaster]

I went to 165 and never looked back the less severe hip angle really helped.

[ghisallo2003]

Do I see from the Stages picture (Cycling News - carbon crank July 21st) that Froome is on 167.5?

[KWalker]

I'm back on 175s. Have em on the MTB and road bike. I found that the switch did not affect aerobic performance, but hampered leverage on higher gradients enough to where I could not maintain my self selected cadence as well. The self selection part is key, not the cadence necessarily itself.

[boots2000]

I echo what Karsten says.
I played around with 167.5 cranks on my tt bike back in 2010.
They felt great- especially at easier efforts. But I found that I lost power on rises and climbs.
I think shorter cranks work if your issue is impingement or poor hip mobility- otherwise stick with the same as you normally ride.

[KWalker]

And I will add that one reason for trying them was the health of my glute on the side of a recent hip break. Taking stress off of that glute did not actually help it recover any faster or respond differently to efforts.