Crank length change .

[Vetseun]

WHO CARES JUST RIDE YOUR BIKE!

+100000

[Eugene]

172.5 requires less torque and you will get on top of the gear quicker and also get to peak power quicker.

 

I would change the mtb if possible to 172.5 and have them both them same. The difference will be felt almost immediately like you have on the road bike.

 

2.5mm is a difference when turning it over, it is not about the shorts propelling you up, that’s like saying adjust the saddle height to accommodate. It’s about the crank and turning it over and being economical.

 

This is often forgotten between road and mtb

For 2.5mm?

 

99% of us would never notice the difference.

['Dale]

WHO CARES JUST RIDE YOUR BIKE!

Contact points, Baby

Gotta get it dialed in, just right ????

[Vetseun]

Contact points, Baby

Gotta get it dialed in, just right

We not all on your level Bud.You do it a touch above the normal cyclist.

But as the Gentleman that you are, you always remain humble.

And I also understand that from your sports science background. Perfection is the goal!

[fanievb]

2 Road bikes, one 172.5 (54cm frame) the other 175 (52cm frame). I prefer the longer cranks.

[Vetseun]

2 Road bikes, one 172.5 (54cm frame) the other 175 (52cm frame). I prefer the longer cranks.

My vrou geniet ook my langer voe.... Ag nevermind.

Kan jy daadwerklik n verskil tussen die verskillende lengtes voel?

Eerlike vraag.

Jy het my aan die dink.

[fusion01]

I have ridden 175mm cranks my whole life , on road , track and now Mtb . I recently bought a Dura Ace group set with 172.5 length cranks . I have been riding them for about 2 months on my road bike and feel comfortable and have no niggles in my legs . My Mtb still has 175 cranks . Do i leave the  saddle on my road bike as is or should i raise it the 2,5mm difference . Will it help anyway or i just leave well alone . . 

Shorter cranks have been said to be better in terms of performance and there is quite a bit out there on this within the interwebz. But frankly 10mm etc is next to no difference you would feel. If you were into MTB and hucking it over rock gardens as I do in Toaki then a shorter crank is less likely to get hit / scuffed due to more clearance. But you have clearance on the road (less rocks!), except for twats in cars.

[ashortchase]

Contact points, Baby

Gotta get it dialed in, just right

It's all in your head

[DieselnDust]

Interesting comment. I would have thought that 172.5 would require more power/torque than 175 as the lever length is now shorter. I would believe that it would be easier to spin and maybe there is where the difference is.

 

 

your hip angle is reduced so you use the hip flexors more effectively. 170mm may be even better. 

The science is starting to show that the shortest cranks you can accommodate is better than longer cranks in tems of the physiological gains, despite the loss in mechanical advantage

Edited March 21, 2021 by DieselnDust

[Jewbacca]

I'm a 170mm road and MTB.

 

I notice a difference straight away but as a hacker amateur it doesn't 'make' a difference. If that makes sense.

 

But having 170mm cranks is more comfortable for my mini primate legs so I ride them

[sirmoun10goat]

I'm sure this is all incremental gains, maybe peak a few watts higher, or the ability to hold a few more watts for longer

 

Nothing that will change the greater community of cyclists from average cyclists to competive vets or semi pros

 

I also think bike manufacturers use small cranks, as there is a marginal weight benefit

[Grease_Monkey]

I also ride 170mm, my mtb was designed around it having a low bb and all - less rock strikes. I do notice a big difference in comfort compared to 175mm cranks. With the longer cranks I always felt like my knees came up too high to my chest, and I always felt like I needed to raise my saddle - but then it would be too high and my hips would rock and I'd get back pain. With the shorter cranks things just feel more proportionate to my short legs. For reference I am 178cm with very short legs and a long torso.

 

You buy a frame, handlebars, saddle based on your size / proportions, why should cranks be any different?

 

As for power / torque / etc, I am sure it makes a difference, but I can't say I can feel it because I ride a trail bike at very average pace and I don't use a power meter. All I can say it I feel better when I am confortable, and shortee cranks are more comfortable for me.

['Dale]

It's all in your head

If it was all in my head then 175mm would be the same length as 172.5mm

So you are out of your mind, Cupcakes

[GrahamS2]

Longer lever = more torque. 

Longer lever makes more torque, shorter lever requires more torque to do the same work.

The lever is a torque multiplier - the longer the lever the higher the multiple. 

[Me rida my bicycle]

The first time I took a spin on my short cranks I noticed it but I dropped by 10mm. I dropped because of my short legs, I had my crank length worked out and it's definitely more comfortable for me. Spinning is easier and to keep a constant pace.

[NickGM]

Longer lever makes more torque, shorter lever requires more torque to do the same work.

The lever is a torque multiplier - the longer the lever the higher the multiple. 

The interesting thing is with a longer crank your rotational speed decreases proportionally. The net effect is that within quite a large range of crank lengths, there is zero/negligible change in power output. ie: torque goes up, rotational velocity goes down in  "zero sum" way. This holds true over a MUCH larger range than the typical spectrum of 170-175mm. Some tests indicate that there is only a noticeable loss in power output once you get down to about 145mm crank length. Apparently anyway, I read up on it quite a bit when building a up a bike during lockdown and the only cranks I could find were 170mm (I'm 1.84cm so "shouldn't" be using cranks that short). 

 

Interesting read:

https://www.bikeradar.com/advice/sizing-and-fit/what-is-the-best-crank-length-for-cycling/

 

Bottom line: crank length within the commercially available range has almost zero impact on power output. However what is noticeable is comfort. Shorter cranks result in angles that are a bit easier on the joints. 

Edited March 22, 2021 by NickGM