Bike Fitter Answers The Crank Length Debate! | Side By Side Comparison Of Short VS Long 

In early 2022 I purchased a bike that had 172.5 cranks. That has been my main bike for these last 2 1/2 years. I had been riding 175mm cranks for 12 years prior. A couple of months ago I spent some time riding my older bikes with the 175 cranks. After a week on the longer cranks knee discomfort & pain were greatly minimized and I was otherwise much more comfortable while pedalling. I ended up buying a new crank in 175mm for the newer bike and have never been happier. I'm 5'10" with a 34" inseam. I don't rock around or bounce off the saddle. I've spent a lot of time riding rollers indoors, especially during a period around 10 years ago. Smooth pedalling is a function of technique much more so than crank length.

I'm still curious why so many manufacturers decide to use overly longer cranks? i.e. I have a Pinarello F5 in a 43cm frame and it comes with 170mm crank arms. Many people that I speak to are between 5'9 - 6'0 and using 165mm cranks. I'm 5'2 with a 28" inseam, so my ideal crank arm is around 150mm. This was the first thing I changed, including the bb before riding my bike to prevent any further injuries. A 43cm frame fits those who are roughly 4'10 - 5'3, cranksets are the most used component on the bike, these should be sized accordingly. I would even go as far as blaming Shimano, SRAM, and Campagnolo for not manufacturing smaller crank arms, leaving us to seek third party manufacturers. My 2 cents

I hava going from 172,5 to 165 cranks and it have helped me a lot. IAM much stronger on longer rides.

Question. You are making observations about mm adjustments to crank length, saddle height and front end. How did you verify/guarantee that the running shoes were at the same exact place on those flat pedals every time, to within the mm? Secondly, on such a video, wouldn't it have been worth it to have rider in road cycling shoes with clip-in pedals? Seems like a massive oversight. I stopped the video when you showed side by side, and the right foot was about 10mm differently set on the pedal. Check it. I'm not saying your observations are incorrect, just that the person riding is giving feedback about "feel", so foot position matters, a lot.

I went from 172.5 to 165 mm, Cadence increased instantly from 85-92 to 92-102 rpm sustained very easily. I can say with certainty that I can maintain the same power in the pedals much easier at a higher cadence, probably combined with a much reduced leg extension

another thing for people to obsess about. will it make a massive difference .... no... ive a road bike with 172.5, a road bike with 170 & a track bike with 165. The increased cadence with the 165 & is noticeable from the 172.5 but unless you're aiming at peak performance or racing then whatever you feel most comfortable with is the right decision...

The whole torque argument was always obvious BS, unless you were spinning out your top gear; otherwise you could just change up if you had excess leg force available.

Great explanation

I’d like to buy shorter cranks but can’t seem to find too many options here in the states. I’m particularly looking for 155 mm that doesn’t cost an arm and a leg

Wow I’m excited about this channel!

I went from 170 to 160. I love the shorter cranks. The difference is too wide in your tests (155 to 185). Can you go through the rest of the sizes? maybe measure power, speed and cadence?

Today you have easy gears so you can climb steep mountains while sitting. In the past you had to get out of the saddle. Did that have an impact on the crank length?

Indurain used 180 mm cranks. Greg Lemond 175. Ole Ritter also used long cranks. (he had the hour record before Merckx) Today Pogacar uses 165 mm. So, what's right or wrong?

An excellent video! Experimented with different crank lengths in last 12 months, as example to your explanation I’m 186cms and riding 165 (TT) and 170mm (road) cranks depending on bike. Landed on both after torque analysis but before I got to the numbers the main driver was how they felt Look forward to more quality content 👍

Great explanation. Thank you

That torque issue, i believe it is adressed if we have plenty of gears.

I love longer cranks myself, tried many lengths over the years.

Key word being “in relation to your body type”. If you close your hip angle, you produce less power, so then either raise the seat (which may not be best thing to do - causing over extended knees and saddle rock) or use shorter cranks but only to the crank length you stop doing these things. Now, if your hip angle is open even with longer cranks - by all means - take the extra leverage for more torque, you will experience less fatigue, and ride for longer and faster than with cranks that are too short for you. There is no universal rule, crank length is a very specific thing to each individual, and recommending shorter cranks as it became fad today is simply wrong, but I understand and also see people toe down pedaling while rocking in the saddle more often than not. Anyway, advantage of either as analogy is short vs long stroke car engine pistons: short stroke revs faster and produces more power and less torque, while long stroke produces more torque and less power. Race car vs locomotive. At this point genetics and cardio engine size come into play. To produce more rpm, you must pedal faster, thus expend more energy - think of sprinters or track riders. You can maintain same speed through applying torque by pedaling at slower rpm and higher gear while expending less energy, having the aid of longer and heavier leg momentum - think of time trialists and strong domestiques. It all comes into play what works for you and you only.

Awesome video guys 🎉

years ago I used to ride a road bike with a crank length of 170-172.5, then I tried to ride a fixed gear, which usually has a shorter crank arm installed in stock (165). As far as i remember, it just feels smoother and easier to pedal, i can spin faster without my bum moving up and down on the saddle. my femur is long ,179cm height with 83cm inseam

Shortening cranks INCREASES gain ratio, mathematically equivalent to up shifting to a harder gear, of course longer cranks "feel easier", it's Leverage 101. Find Sheldon Brown's Gain Ratio page. Basically it's the ratio between bike travel distance vs foot travel distance, usually considered through one revolution of the cranks though it extrapolates out and holds to any distances. Please, look up the definitions of "Scientific Theory" (if it's not a Scientific Theory, it's not a "theory" at all) and "hypothesis" and never conflate the two again. Sorry, your sharpie drawn graph is no substitute for measured and repeatable dynamometer numbers, if you've no dynamometer access, how are you a "bike fitter"? Is there an ideal ratio between crank length and upper and/or lower leg length and how was it determined and can any bike fitter empirically confirm and apply it?

185.5cm and 172.5mm works great. I had 175mm and those also felt great, but I think my heart rate went up faster when it was longer because peak torque is greater. 170mm feels quite fast, but weak when standing or sprinting.

I have 2 bikes,one has 195mm cranks and the other has 225mm.

I'm going to be switching from 172.5 to 165's soon. So you only move saddle height up 7.5 not back at all?

Why do manufacturers build bikes with a standard crank length of 170 mm (even for small sizes) if this length is too long for many people? Don't they know what you know?

5mm crank length difference between my road & gravel (170mm) and my MTB (175mm) Feel no tangible difference. Before this was a thing, I rode on stock cranks for years without even thinking, now we are clearly overthinking it.

Do you also adjust saddle fore-aft with a change in crank length?

8:25 haha what

You should have had her wear a shoe that didn't have such a large stack which would have made it feel worse. So straight away you have biased the talk . So I just turn off at 4.09 into the video .