You Should Be Using Shorter Cranks, Here's Why

Shorter cranks are the newest trend in performance cycling, but does this trend actually have any merit? Today we take a look at what the research has to say about how crank length affects power output to determine whether or not you should make the switch.

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Research used in this video:

[jkevincarmichael]

Dylan, FWIW I did my masters thesis in like 1980 on the effect of cranklength (150-200 mm) on oxygen consumption while cycling at a constant workload. I used competitive cyclists and the results did favor shorter cranks. The limitation was clearly that other than time trials the workload in cycling is constantly changing. At 6'1" I continue on 175's as that is what I am used to and have no other issues to address....except being 70 years old.

[TheTinyCyclist]

I'm going to order a 15mm crank. Thank you, Dylan.

[AlanJames]

Thanks Dylan, I can now use my long cranks as an excuse for not being aero or fast enough.

[CamNicholls]

The bloke with bad hips and knees. 👋 thanks for the shoutout Dylan 🤣 top vid as usual

[Vjhuh]

welcome back Dylan!

As a fitter from my side I can add: these marginals gains come not from biomechanical side of the leg-crank system, but physiological one. With exertion, muscle mobilizers/stabilizers come into account, when those enduracne depletes and leg pattern is distured, thus cutting effective pushing phase of legs in degrees significantly. So shortnening the open/close leg angles saves mobilizers/stabilizers for longer period of time.

Cheers,
Alexey

[ttbikefitdotcom]

Great video. As a pro bike fitter that does 75% tri fits, we have been onto this for some time now for the exact reasons you mention: hip angle tends to be the limiter in the TT/tri position, and you can only get so far forward (steep seat angle) before the weight distribution becomes silly. So shorter cranks, which reduce the knee height at top of crank cycle are the answer. Average size folks do indeed tend to gravitate to 160 or 165mm for tri (so the 18-20% crank length/inseam holds). We can switch crank lengths on our Vertex Fit Cycle while the rider is still on board and instantly adjust saddle height while keeping all other parameters constant, so it is easy to observe the rider's reaction to different crank lengths. Frequently 1-2 sizes shorter than they are accustomed to results in a very positive perception as far as power and efficiency. I hear "did you drop the power - this is easy now" all the time. (I don't drop it). At some point tho the rider dislikes the change - they become too short. Now this is likely affected somewhat by anchoring to their traditional crank length. But that said, after 10 mins on the new shorter cranks, I switch them back to their traditional length and they hate them. They may have been riding 172.5 for decades, and after 10 mins on 165 they hate the 172.5. I have never seen anyone (thousands of fits) go longer again. Road is less cut and dry than tri/tt, it's far easier to get away with long cranks for road as many riders aren't hip-angle limited on a road bike (shorter riders tho typically are). But for sure the knee flexion thing can be significant. I had a very tall guy who had struggled with knee pain his entire life - but he loved cycling and so rode thru the pain for decades. "Laughably short" 155mm cranks (~37" inseam so 16% crank length/inseam) cured him instantly. One easy test for the reasonableness of traditional 165-175 crank lengths: that's a 6% variance in lengths. Saddle heights commonly vary more than 40%.

[derekhartloper]

Hi Dylan I suggest that out of saddle climbing is benefited by longer cranks, as torque is linearly related to crank length. So for the same applied power, your applied torque will increase. 175mm cranks will increase torque 6% over 165mm. That's obviously a significant advantage on climbs.

[kareltempelaere]

I went from 172.5 to 165 and got much less knee pain and saddle sores due to a more stable position. I also noticed a significant improvement in performance and speed, maybe due to the increased comfort and the ability to get more aero but the benefits have been very noticeable. great video hope manufacturers will catch on because not finding any bike that fits me anymore is a pain in the ass (even "custom" bike builds often don't feature anything below a 170)

[musclelessfitness]

Finally ! a Dylan Johnson video !
I changed from 170 to 160 and I love it. I love the shorter cranks for these reasons :
1 - no more fear of pedalling in corners (I still have to be cautious)
2 - no more hitting the front tire if I turn my handle bar a lot
3 - faster cadence, even when I'm not trying.
4 - less knee and hip pain

I might try 150 or 155 mm on my second bike ... we'll see

[sedrickchan]

I've been watching your clips since 2020 and it's good to see you back after a while!

[davidlilja]

Dylan, welcome back to science! We all been dying out here as we waited. 😉
At 6'2" on 61cm framesets, I moved to 180s 16 yrs ago but when I revamped my bike positioning earlier this year, dropped to 165s. Knees are now 30mm lower, stem is lower & longer and my short saddles are forward now too. I'm no pro but it's working for me.

[BrightLight]

I went from 170 to 160. No toe overlap, no pedal strikes, slightly higher cadence, and most importantly it just feels better.

[christopherbritton]

I have been riding for 30 years, and I switched from 170mm to 165mm cranks. I did several tests of 3 different TrainerRoad sessions over several weeks. And I consistently pushed 20watts more at 5bpm less.

[lolbubs]

I'm 6' and ride L/XL frames. I rode 165 cranks my whole childhood / college (I think my dad was mostly motivated by reduced pedal strikes at high lean angle). Then my first carbon bike purchased as an adult came with 172s, so I have that on my road/gravel bikes. But on the track, shorter cranks are advantageous because comfort and efficiency at high RPMs is such a big factor (also pedal striking at some velodromes, though not mine). So on track, I run 165s. They certainly feel a little different but I don't think it's a big deal. I only race track and the 172s on the road aren't bugging me, so I'm not rushing out to replace them ($$$). Interesting video!

[jacoblopez]

“Dude, that’s what I been trying to tell my girlfriend”😂same buddy

[clinlashway]

I'm 6' 2", but have a long back and relatively short legs with an inseam of 32.75". A new bike I got several years ago came with 175 mm cranks. I quickly noticed left knee pain. I switched to the 172.5 mm I had been using and this resolved. But sometime after that, I started getting more left knee pain. I looked into still shorter cranks and decided 165 mm looked good. I tired them and the knee pain dropped to a fraction immediately and was completely gone within a few weeks. I then converted all of my bikes to 165 mm.

My short wife had 165 mm cranks on her bike. I converted to 152 mm and she immediately loved it. I could also see that she no longer looked like she was going to hit herself with her knees while pedaling.

You do lose some leverage, but it's on the order of a half a step between gears and you only lose something at the very lowest gearing. I also believe the less range of knee motion means more of your pedal stroke is in a strongest or best leverage portion of the pedal stroke.

Bottom line, I'm a believer in shorter cranks.

[harryparkinson]

For offroad, shorter cranks also have the advantage of less pedal strikes

[laggypirates]

What's crazy is that in spite of the shorter crank trend, crank lengths on new bikes are still based on frame size and not an option by most manufacturers.

[larrylem]

For the same hip and knee flexion from folks 4'6" to 6'6", we should be seeing a much greater range in crankarm lengths.

[prosoccer]

So glad to see these videos are back! Can't wait to hear your latest tire testing results with the race kings and would love to hear your thoughts on all of the available suspensions systems for gravel racing. Thanks!