Crank length myth

michaelvs said:

Hi all,

Please help! I have heard that it is best to ride longer cranks if you want to climb better? maybe only for long steady climbs but not for the shorter climbs where the pace can be inconsistent?
And how would this affect the rest of my racing, eg: sprinting etc?

Thanx

It seems to vary on a per rider basis. The current world hour record holder used 190mm cranks and it's rumoured that Indurain used some custom made 190mm Campag Record cranks to one or more of his Tour victories.

I tried lengths from 165mm to 185mm when I was racing years ago. I found that I climbed and time trialed better on the 185mm but I was having issues, due to lack of flexibility, staying at 90+rpm for a couple of hours. Riding was noticably easier if I followed a regular stretching plan - but due to time constrains etc etc that was normally the first thing that was forgotten about.

I recently tried 185mm on my Powercranks (in PC mode) and well.... lets not go there. It wasn't a good experience. It gets better with time and stretching but lets just say I'm about as inflexiable as it gets cyclist wise. LOL.

I also tried 220mm (in lockout fixed crank mode) on a 1.5 mile section of 20% and steeper. I like.... but there's no way in hell that I can use that crank length in regular PowerCrank mode. None.

Admitting PowerCrank usage and the use of cranks longer than 175mm in one post! Send me off to the gallows before the questions begin! 🙂

Currently at 180mm. My inseem is 34.5" for those who are curious.

That's a new one on me. I personally think you climb better with slightly shorter than usual cranks, for sustained seated efforts. My Computrainer seemed to indicate that I was more efficient (some will say smoother) with a 170 than a 172.5 (5'7" with a 29 inseam). But, for all around riding I prefer the 172.5.

Now for SPRINTING, or out of the saddle climbing, I could see a slightly longer crank being helpful. Racing BMX I always used a 180. Coming out of the gate first and getting into a leading position is crucial, but then again that is a very different type of riding.

For MTB, standard 175mm has always suited me well, personally.

The best way to really know would probably be to use a Computrainer or power meter of some type (reliable) and use several different sizes over a course that you are looking to be your best on, seeing which crank gives you the best overall power curve.

in my opinion, the only time longer cranks win hands down is when riding off the saddle, where you get the benefits of the leverage without being in a weird position. The problem with long cranks is that they're a little harder to push when seated, because your feet come up much higher.

I'm 6ft with long legs, and I tried 180s for about a year. I liked them at first, and they were great off the saddle for short hill efforts, but I ended up being frustrated at not being able to "get on top of" the pedals to really push when I was seated. The day I went back to 175s I felt so much higher over the pedals, and much more powerful. I could really pound the pedals coz I was 'on top of' them, rather than having my knees in my chest. 🙂 With the 175s feeling immediately so good, I quickly tried 172.5s and 170, and I now mostly ride 172.5s, although I think 175s might be my best length.....

I now ride

freeagent35 said:

Now for SPRINTING, or out of the saddle climbing, I could see a slightly longer crank being helpful. Racing BMX I always used a 180. Coming out of the gate first and getting into a leading position is crucial, but then again that is a very different type of riding.

Typically, track sprinters don't ride excessively long cranks as high power and high leg speed is crucial for success.

I had to laugh - a club mate and friend yesterday just broke the world's best 2km individual pursuit time in her age category (WMAS 35-39) during the final of our State Masters Track Championships. Afterwards she came over to chat and asked me about increasing her crank length from 170 to 175mm.

My initial response was -"You just broke the world record on the 170s, why on earth would you want to change now?"

Ride whatever you feel comfortable with for the event you ride, crank length is a bit of a red herring.

I don't know if I'd go as far as saying it's a red herring... but like anything else the "mystery" is finding out what works best for you.

Alex Simmons said:

crank length is a bit of a red herring.

Hmmm. That's pretty catchy.

RChung said:

Hmmm. That's pretty catchy.

Haddock you said anything else then you might have been dancing to a different tuna.

I'm gonna have to get out of this Plaice, if it's the last thing I ever do...

swampy1970 said:

Haddock you said anything else then you might have been dancing to a different tuna.

A bit flakey, or maybe you're just breamming with confidence.

Anyway, that's my John Dory and I'm sticking to it.
🙂

swampy1970 said:

I'm gonna have to get out of this Plaice, if it's the last thing I ever do...

"we gotta get out of this place
girl there's a better life for me and you"

:p

circa 1986 :eek:

Thanx guys,

I'm 6 ft 1' and ride 172.5mm, but now I'll try the 175mm and see what a difference it make to my climbing and power.

Take care

Alex Simmons said:

Ride whatever you feel comfortable with for the event you ride, crank length is a bit of a red herring.

I agree.

Especially since the typical crank length difference a particular rider tries is only 5 mm. And this 5 mm equate to about 3 %. Cadence, gear ratios and sitting position normally are differing way more.

carmol said:

I agree.

Especially since the typical crank length difference a particular rider tries is only 5 mm. And this 5 mm equate to about 3 %. Cadence, gear ratios and sitting position normally are differing way more.

I agree that the length difference is small %-wise and I also agree that just moving around on the saddle can change even more than that.

However, when I changed from 175 mm to 170 mm cranks on my TT bike*, I found that a huge difference in cadence was required to maintain the same power. I think it was something like 10-13 RPM for me. Though I eventually got used to it, because I had become such a "masher" before the change, it was a big struggle to adapt.

* I run a tight aero position, approximately a zero degree torso angle with respect to the top tube or the ground. I went to shorter cranks due to my large rib cage interfering with my femurs at the top of the pedal stroke.

Steve_B said:

I agree that the length difference is small %-wise and I also agree that just moving around on the saddle can change even more than that.

However, when I changed from 175 mm to 170 mm cranks on my TT bike*, I found that a huge difference in cadence was required to maintain the same power. I think it was something like 10-13 RPM for me. Though I eventually got used to it, because I had become such a "masher" before the change, it was a big struggle to adapt.

* I run a tight aero position, approximately a zero degree torso angle with respect to the top tube or the ground. I went to shorter cranks due to my large rib cage interfering with my femurs at the top of the pedal stroke.

Perhaps a dumb question, but couldn't you have just changed gears?

Steve_B said:

I agree that the length difference is small %-wise and I also agree that just moving around on the saddle can change even more than that.

However, when I changed from 175 mm to 170 mm cranks on my TT bike*, I found that a huge difference in cadence was required to maintain the same power. I think it was something like 10-13 RPM for me. Though I eventually got used to it, because I had become such a "masher" before the change, it was a big struggle to adapt.

Hmmm. You realize that the circumference of your pedal stroke only decreased from 1099.56mm to 1068.14 mm right? That's a 31.42mm decrease or ~2.86% going from 175's to 170's. Not sure where you started from for cadence on your TT rig. If you were at 100 rpm you would only need to go to ~103 RPM to generate the same power. Sounds like you found some additional fitness or your original position was limiting you.

WRT crank length in general, I believe that it's much more a matter of fitting to the individual rider. As mentioned earlier in this thread, leg length, femur length, flexibility, and other structural particularities all play a part in determining optimum fit. The "rules" only provide a starting point from which to tweak from.

Dave

dkrenik said:

Hmmm. You realize that the circumference of your pedal stroke only decreased from 1099.56mm to 1068.14 mm right? That's a 31.42mm decrease or ~2.86% going from 175's to 170's. Not sure where you started from for cadence on your TT rig. If you were at 100 rpm you would only need to go to ~103 RPM to generate the same power. Sounds like you found some additional fitness or your original position was limiting you.

WRT crank length in general, I believe that it's much more a matter of fitting to the individual rider. As mentioned earlier in this thread, leg length, femur length, flexibility, and other structural particularities all play a part in determining optimum fit. The "rules" only provide a starting point from which to tweak from.

Dave

No.... 100rpm in a given gear gives the same power and therefore same speed regardless of crank length. It's the force at the pedals that changes with crank length. The chainrings don't care how long the cranks are.... 😉

swampy1970 said:

No.... 100rpm in a given gear gives the same power and therefore same speed regardless of crank length. It's the force at the pedals that changes with crank length. The chainrings don't care how long the cranks are.... 😉

Doh! I sit corrected :o
Dave

swampy1970 said:

No.... 100rpm in a given gear gives the same power and therefore same speed regardless of crank length. It's the force at the pedals that changes with crank length. The chainrings don't care how long the cranks are.... 😉

Nothing wrong about what you've said here, but since pedal force is the prime mover I'd phrase it that shortening the cranks means you are getting less torque for the same pedal force as you were applying before. You'd have to increase cadence (or gearing) proportionally to overcome the reduction in torque if you wanted the same power output as before.

Edit: IOW, you guys are saying the same thing but looking at it from different ends of the bike -- Dave wants to increase cadence and Swampy wants to increase pedal force. 🙂

swampy1970 said:

No.... 100rpm in a given gear gives the same power and therefore same speed regardless of crank length. It's the force at the pedals that changes with crank length. The chainrings don't care how long the cranks are.... 😉

yeah but what if you were driving a human-powered light airplane .. or <g> a nuclear sub in the Gulf stream? :p

rmur17 said:

yeah but what if you were driving a human-powered light airplane .. or <g> a nuclear sub in the Gulf stream? :p

I've ridden a stationary bike *on* a nuclear sub in the Gulf Stream. Talk about confusing.... :p

frenchyge said:

Nothing wrong about what you've said here, but since pedal force is the prime mover I'd phrase it that shortening the cranks means you are getting less torque for the same pedal force as you were applying before. You'd have to increase cadence (or gearing) proportionally to overcome the reduction in torque if you wanted the same power output as before.

Edit: IOW, you guys are saying the same thing but looking at it from different ends of the bike -- Dave wants to increase cadence and Swampy wants to increase pedal force. 🙂

No I don't, that's why I ride 180mm PowerCranks. :p I used to ride 185mm TA Alize cranks but that's when I didn't have a BBQ and beer induced gut. :eek: You should try 220mm cranks whilst seated on a 25% hill. Where's the *love* emoticon when you need it - but just don't ask me to pedal at more than 70rpm on those! I can see yoga classes in my future though!

A 13 rpm difference sounds like a 2 or more sprocket increase... A drastic change but each to his own I guess.