The Effect Of Crank Length On Performance
I have both 165mm and 170mm cranks and have used both at different times in my riding at the velodrome. I used to feel that the 170 allowed me to turn a larger gear and the 165 cranks allowed for more cadence. I had no research at all to back my opinion up with, I think it was something told to me a long time ago. Is there any truth to those two beliefs? |
I've seen a lot of holy wars started over crank length on different forums over the years, but the tl;dr is - if you're fairly normal proportioned (not extremely tall or short) you can ride pretty much anything (commercially available anyways) without it having much if any effect. The current thought is to use crank length as a fitting tool (and also taking special consideration for something like track where too long and you risking clipping a pedal) and letting the rest sort itself out naturally.
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Watch this:
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I sometimes feel like I'd rather have shorter cranks on my road bike, as my track bike just feels better to pedal with 165s versus 172.5s on the roadie but haven't had the means to try it. There could also be a multitude of other things at work there. Shorter cranks don't require as much movement at the hip to spin, so it does make sense that they'd be easier to pedal at higher cadences. Interesting little convo on crank length from a bike fitter's perspective here, around the 4:00 mark:
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Originally Posted by colnago62
(Post 20632666)
I have both 165mm and 170mm cranks and have used both at different times in my riding at the velodrome. I used to feel that the 170 allowed me to turn a larger gear and the 165 cranks allowed for more cadence. I had no research at all to back my opinion up with, I think it was something told to me a long time ago. Is there any truth to those two beliefs? As far as the the gain ratio and "feeling easier", the cranks do give you a tiny increase in leverage, but that 5mm might be able to be offset by the fact that your hip angle opens because your TDC drops 10mm, which moves your weakest part of the pedal stroke into a stronger range of motion, and shortens the the window of time you spend here because you reach fuller feg extension earlier in the pedal stroke. In other words, although longer cranks give you more leverage at the pedal interface, shorter cranks allow more of the pedal stroke to be spent in a more powerful muscular range. |
Originally Posted by Morelock
(Post 20632681)
I've seen a lot of holy wars started over crank length on different forums over the years...
In my experience, it comes down to riding style and event focus and less about height. For example, bike check interviews have had Sarah Hammer on 172.5mm cranks and Jamie Staff on 165mm cranks. Crank length is important for unlocking that last 10% or so of power and speed. The thing is, you may have already lucked-up and started with your optimal crank length...you just have to experiment. |
Originally Posted by taras0000
(Post 20632801)
These are both true. In one of the other threads around here, someone ( I think Carleton) calculated the gain ratio difference between 165 and 170 cranks, as well as the difference in foot speed given the same rpm for each crank. If I remember correctly, the gain ratio wasn't a huge difference, but the foot speed differential was greater than one would think.
So, this is why racing 170mm cranks on a 98" gear feels like racing 167.5mm cranks on a 96" gear. You lose leverage...but you gain more effective cadence ranges and knees don't come up as high, so you can bend over more. Then there is "tangential velocity" of the foot spinning around the shorter or longer cranks. It's a mess of calculations :foo: I've done them. There is also mention of it in the Bicycle Science book. I'll see if I can dig out the formula they came up with that involved crank length, chainring, cog, and torque. |
For me, my times are very similar between the cranks. I am asking because I am going to buy a crank based power meter. I am leaning towards 167.5 |
Originally Posted by topflightpro
(Post 20632784)
Watch this: https://www.youtube.com/watch?v=5i9DtIFi9pM
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I am 5"5" tall and currently using 165 mm cranks. I am thinking of changing to 150 mm for next year. I haven't been very successful in finding a 155 mm set in 144 BCD. Does anyone have any suggestions?
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Originally Posted by rensho3
(Post 20633141)
I am 5"5" tall and currently using 165 mm cranks. I am thinking of changing to 150 mm for next year. I haven't been very successful in finding a 155 mm set in 144 BCD. Does anyone have any suggestions?
Their website is jacked up now. So, I'm not sure what their offerings are. Here is a pic I snapped of Ken Lo's cranks. They are 150 or 155mm (I can't find my notes). I don't think they are custom. You can (or at least could) get them without a power meter. https://i.imgur.com/l4M2NDa.jpg Maybe ROTOR stopped making them? FYI, Ken Lo is one of the fastest masters Man 1 riders in the US right now. |
You can pretty much use any correct length 3d+, 3d30 rotor crank and buy the 144mm spider separately.
I personally opted to take a Dura Ace 172.5 (solid) and cut it down to 150mm. At my height 5'4", it allowed me to run a bigger effective gear (gain ratio) than when I was using a 165mm. 165 or 170 is okay if you can spin and finesse a lower effective gear, but it didn't really suit my high torque mashing style. |
Originally Posted by rensho3
(Post 20633141)
I am 5"5" tall and currently using 165 mm cranks. I am thinking of changing to 150 mm for next year. I haven't been very successful in finding a 155 mm set in 144 BCD. Does anyone have any suggestions?
Cutting and tapping the arms is not rocket science, but it helps to have a spare set of steel crank arms to use as a guide so the new pedal threads are at the right angle. |
Originally Posted by rensho3
(Post 20633141)
I am 5"5" tall and currently using 165 mm cranks. I am thinking of changing to 150 mm for next year. I haven't been very successful in finding a 155 mm set in 144 BCD. Does anyone have any suggestions?
Crank arms https://rotoramerica.com/collections...ts/aldhu-track Track Spider https://rotoramerica.com/collections...-track-30-axle Track 30 Axle https://rotoramerica.com/collections...u-track-spider BSA30 Track BB https://rotoramerica.com/collections...ts/bsa30-track Beware and get the correct bottom bracket. The axle is 30mm, so get the new track BSA30 BB with the red seals, not the older 24mm track BB with the blue seals (online vendors may not yet know the difference). The Rotor rep said the road BSA 30 does not work. Also, the spider is thin and not countersunk for captive nuts. Dura Ace chainrings don't cinch down with normal track bolts. FSA are reported to work as well as the Rotor track chanirings. https://rotoramerica.com/collections...ack-144bcd-1-8 The older Rotor 3D24 crankset came in 155mm. The spider is removable, and one version of the Power2Max track powermeter used the Rotor 3D24 road crankset. 24 refers to the 24mm spindle. Power2Max also offered a track powermeter using the Rotor 3D+ crank set which used a 30mm spindle. That's what is shown in the Ken Lo photo above.
Originally Posted by tobukog
(Post 20633253)
You can pretty much use any correct length 3d+, 3d30 rotor crank and buy the 144mm spider separately.
https://rotoramerica.com/collections...ts/3d-crankset Check to see if you need a special tool to replace the spider. I know the 3D24 did. |
At the same cadence a shorter crank requires lower foot speed and higher torque. Longer crank is the opposite, higher foot speed and lower peak torque
In reality someone running longer cranks is likely to use a larger gear at a lower cadence, effectively equalizing the peak torque and foot speed. Someone running shorter cranks is likely to use a lower gear and higher cadence, also equalizing peak torque and foot speed. In the end the difference is the cadence and actual gear used. I think the most important thing is that your cranks on all your bikes should be no more than 2.5mm different from any other bike. I can't remember what study this was but that was the main take away I had from reading it. The participants could the produce the same power at any length once acclimatized but changing by more than 2.5mm resulted in a loss of performance until they re-adjusted to the new length. |
Originally Posted by gl98115
(Post 20633322)
The Rotor ALDHU comes in 155mm. To put together a crankset for a BSA 68 track bike, you need :
155mm crankarms https://rotoramerica.com/collections...ts/aldhu-track Track Spider https://rotoramerica.com/collections...-track-30-axle Track 30 Axle https://rotoramerica.com/collections...u-track-spider BSA30 Track https://rotoramerica.com/collections...ts/bsa30-track Beware to get the correct bottom bracket. The axle is 30mm, so get the new track BSA30 BB with the red seals, not the older 24mm track BB with the blue seals (online vendors may not yet know the difference). The Rotor rep said the road BSA 30 does not work. Also, the spider is thin and not countersunk for captive nuts. Dura Ace chainrings don't cinch down with normal track bolts. FSA are reported to work as well as the Rotor track chanirings. https://rotoramerica.com/collections...ack-144bcd-1-8 The older Rotor 3D24 crankset came in 155mm. The spider is removable, and one version of the Power2Max track powermeter used the Rotor 3D24 road crankset. 24 refers to the 24mm spindle. Power2Max also offered a track powermeter using the Rotor 3D+ crank set which used a 30mm spindle. That's what is shown in the Ken Lo photo above. I've always been perplexed by ROTOR's offerings and their mix and match style. I like the idea of mix and match. Maybe they can do a better job of presenting how it all works and how one might craft a solution. |
So I think I am going with 165 length cranks. They feel fine and, based on what I could understand of the videos, shorter is probably better than longer; more advantages. |
Originally Posted by carleton
(Post 20633178)
Here is a pic I snapped of Ken Lo's cranks. They are 150 or 155mm (I can't find my notes). I don't think they are custom. You can (or at least could) get them without a power meter.
FYI, Ken Lo is one of the fastest masters Man 1 riders in the US right now. Leg length is a factor. I'm currently running 170s, and my fitter said normally she would scream about someone running cranks that long, but they work okay for me because I have such long legs. Still thinking about going down to 165s though because the latest science says they are faster. (Per the video I posted earlier.) |
Thanks everyone for all the information. Fortunately, I also know Ken Lo and am going to talk to him about his setup. I never thought to talk to him, which I guess just makes me unaware!
Good to know that Shimano chainrings need a different bolt because most of my rings are Dura Ace. I have some old superbe pros and am hoping they work. I am trying to keep the cost of the conversion down to something manageable. As you get to be an older Master, and living on a fixed income, expense begins to be important! |
[QUOTE=gl98115;20633322]The Rotor ALDHU comes in 150 and 155mm. To put together a crankset for a BSA 68 track bike, you need :
Crank arms Track Spider Track 30 Axle BSA30 Track BB Beware and get the correct bottom bracket. The axle is 30mm, so get the new track BSA30 BB with the red seals, not the older 24mm track BB with the blue seals (online vendors may not yet know the difference). The Rotor rep said the road BSA 30 does not work. Also, the spider is thin and not countersunk for captive nuts. Dura Ace chainrings don't cinch down with normal track bolts. FSA are reported to work as well as the Rotor track chanirings. Is the above crankset a power meter (links removed since I am not allowed to post links)? I am currently riding a 3D Inpower road adapted with a spider adapter to get to 144BCD. I would love to have a dedicated track crankset that is 155 and a power meter. |
Originally Posted by rensho3
(Post 20634704)
Good to know that Shimano chainrings need a different bolt because most of my rings are Dura Ace. I have some old superbe pros and am hoping they work.
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Power2Max now offers two track power meter spiders for the Rotor ALDHU crankset.
https://cimg8.ibsrv.net/gimg/bikefor...796aa0a0c3.jpg https://power2max.cc/collections/nge...-3d-plus-track https://power2max.cc/collections/ng-track-power-meter Interesting, it looks like you use it with the ROAD ALDHU axle and appropriate bottom bracket instead of the track axle and BB. |
Looks like the ALDHU cranks are only available in 170-175.
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Originally Posted by topflightpro
(Post 20635161)
Looks like the ALDHU cranks are only available in 170-175.
https://rotoramerica.com/collections...ducts/aldhu-3d |
Originally Posted by gl98115
(Post 20635248)
You can buy the ALDHU crankarms in different lengths (150, 155, 160, 165, 170, 172, 175) from other vendors.
https://rotoramerica.com/collections...ducts/aldhu-3d |
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