How much torque/power do you lose going to shorter cranks?

[JoeOxfordCT]

Let me start by saying that I have two physical issues that most folks don't have to deal with. I broke my right heel in an auto accident in 2002 and have a strap & screws in my right foot. My right calf since then has always been smaller & weaker. I have also developed "drop foot" in the same right foot recently too, meaning I have nerve weakness pulling up with my toes. When my doc says, "stand on your heels and pick up the front of your feet.", I can't get my right foot off the ground. It is what it is....moving on...

I picked up a CAAD10 last fall and swapped out the standard 172.5 crank for a 175 as I have done for all past bikes. With the weak calf I like the extra climbing leverage of the 175. However, with the drop foot that's developed I now have a rather larger dead spot at the top of my pedal stroke. For $hits & giggles I took my wife's mtn bike w/slicks for a spin the other day as it has 170's. The dead spot was greatly reduced but I did also feel noticeably less power seated climbing. BTW, my inseam is 30". I'm 5'10".

I am going to go to my LBS today and ride the owner's road bike as he runs 170's. I am also going to ride something with 172.5's as well for comparison. I run a 50x36 with an 11-28 in the rear. I live in CT and most rides have a lot of climbing, nearly 100' per mile. I'm a little nervous surrendering so much leverage but I have to admit the 175's are starting to feel a bit choppy. Will I eventually develop more power and/or acclimate to it ?

Thoughts, suggestions, anecdotes ?

 

[elapid]

My one recommendation: do not get sucked into the vortex of the short crank thread elsewhere on this forum.

Personally, I don't think you will find much difference between 170mm and 175mm cranks. Based on the results of studies, as listed below, there is no difference in maximal power with slightly shorter cranks and you will be able to reach maximal power quicker with the 170mm cranks, but because your cadence will be higher (which may be beneficial in a hilly area) with shorter cranks you may fatigue more quickly.

These are the results of studies published on crank length:

STUDY 1

Med Sci Sports Exerc. 2011 Sep;43(9):1689-97.
Effect of crank length on joint-specific power during maximal cycling.

PURPOSE: The purpose of this study was to determine the effect of changes in crank length on joint-specific powers during short-term maximal cycling.

RESULTS: Crank length had no significant effect on relative joint-specific powers at the hip, knee, or ankle joints (P > 0.05) when pedaling rate was optimized.


STUDY 2

Fatigue during maximal sprint cycling: unique role of cumulative contraction cycles.

RESULTS: Crank length did not affect peak power. Fatigue index was greater and total work was less with the higher pedaling rate-shorter crank condition.


STUDY 3

Eur J Appl Physiol. 2002 Jan;86(3):215-7.
Effects of crank length on maximal cycling power and optimal pedaling rate of boys aged 8-11 years.

RESULTS: Power produced when using the 170 mm cranks did not differ from that produced with the crank length that was 20% of estimated leg length (LL20). Optimal pedaling rate was significantly greater for the LL20 cranks than for the 170 mm cranks. Standard 170 mm cranks do not compromise maximal power measurements.


STUDY 4

Eur J Appl Physiol. 2001 May;84(5):413-8.
Determinants of maximal cycling power: crank length, pedaling rate and pedal speed.

RESULTS: Power produced with the 145- and 170-mm cranks was significantly greater than that produced with the 120- and 220-mm cranks. The optimal pedaling rate decreased significantly with increasing crank length. Conversely, optimal pedal speed increased significantly with increasing crank length. Even though maximum cycling power was significantly affected by crank length, use of the standard 170-mm length cranks should not substantially compromise maximum power in most adults.


STUDY 5

Eur J Appl Physiol. 2010 Jan;108(1):177-82. Epub 2009 Sep 22.
Influence of crank length on cycle ergometry performance of well-trained female cross-country mountain bike athletes.

RESULTS: The aim of this study was to determine the differential effects of three commonly used crank lengths (170, 172.5 and 175 mm) on performance measures relevant to female cross-country mountain bike athletes of similar stature. The time to reach supra-maximal peak power was significantly shorter in the 170 mm condition compared to 175 mm. This effect represented a mean performance advantage of 27.8% for 170 mm compared to 175 mm. There was no further inter-condition differences between performance outcome measurements derived for the isokinetic (50 rpm) maximum power output, isokinetic (50 rpm) mean power output or indices of endurance performance. The decreased time to peak power with the greater rate of power development in the 170 mm condition suggests a race advantage may be achieved using a shorter crank length than commonly observed. Additionally, there was no impediment to either power output produced at low cadences or indices of endurance performance using the shorter crank length and the advantage of being able to respond quickly to a change in terrain could be of strategic importance to elite athletes.

 

[ustabe]

I am going to go to my LBS today and ride the owner's road bike as he runs 170's. I am also going to ride something with 172.5's as well for comparison. I run a 50x36 with an 11-28 in the rear. I live in CT and most rides have a lot of climbing, nearly 100' per mile. I'm a little nervous surrendering so much leverage but I have to admit the 175's are starting to feel a bit choppy. Will I eventually develop more power and/or acclimate to it ?

Thoughts, suggestions, anecdotes ?

I went from 170 to 175 and noticed an improvement in my climbing and rolling, with a proportional loss of of rpm and snap in my sprint. I've stuck with the the 175s, the spin returned, as did some of the sprint.

My legs are also about 5" longer than yours. Your legs are short relative to your total height.

With your leg length and the difficulty you're relating, I'd be inclined to say use a shorter crank and compensate for the loss of torque by developing a faster, stronger spin. I don't think it's impossible for you to become efficient at 175s, but I do think the costs might outweigh the advantages.

 

[JayKosta]

Shorter cranks will allow you to 'spin' easier because the circumference of the pedal circle is smaller.
But if your current gearing requires maximum torque in the lowest gear to get up the hills, you might have a problem.
Remember tho... a 5mm difference from 170mm is only about 3%.

My guess is that lower gearing with a comfortable crank length would be the best solution.

Jay Kosta
Endwell NY USA

 

[FrankDay]

Let me start by saying that I have two physical issues that most folks don't have to deal with. I broke my right heel in an auto accident in 2002 and have a strap & screws in my right foot. My right calf since then has always been smaller & weaker. I have also developed "drop foot" in the same right foot recently too, meaning I have nerve weakness pulling up with my toes. When my doc says, "stand on your heels and pick up the front of your feet.", I can't get my right foot off the ground. It is what it is....moving on...

I picked up a CAAD10 last fall and swapped out the standard 172.5 crank for a 175 as I have done for all past bikes. With the weak calf I like the extra climbing leverage of the 175. However, with the drop foot that's developed I now have a rather larger dead spot at the top of my pedal stroke. For $hits & giggles I took my wife's mtn bike w/slicks for a spin the other day as it has 170's. The dead spot was greatly reduced but I did also feel noticeably less power seated climbing. BTW, my inseam is 30". I'm 5'10".

I am going to go to my LBS today and ride the owner's road bike as he runs 170's. I am also going to ride something with 172.5's as well for comparison. I run a 50x36 with an 11-28 in the rear. I live in CT and most rides have a lot of climbing, nearly 100' per mile. I'm a little nervous surrendering so much leverage but I have to admit the 175's are starting to feel a bit choppy. Will I eventually develop more power and/or acclimate to it ?

Thoughts, suggestions, anecdotes ?

Our experience is most actually will see a small power increase going down to as small as 145 and even shorter. Be aware that, depending upon where you are starting, that this change has the potential to also affect your aerodynamics (I recently went to the wind tunnel to look at this). There is a long thread in the form and fitness forum discussing all of this if you are interested.

 

[Boeing]

dear god say it isnt so. nnnnnooooooooooooo not here please anywhere but here

 

[stainlessguy1]

crank length

:All good research by the posters on this thread . so i wont go over it again.

Given your injuries and height and leg length the crank length of 172.5 mm would be max . I recommend to go to 170.mm and use all those new small gears that are ridden today .

WE used crank lengths of 175 and we were tall blokes at 6ft 2 and taller with much longer inseems . WE road a 54/42 or 43 with a 13 to 18 block as almost standard. A mountain block for me would of included up to a 21 as the final . That was all on steel frames which were still many pounds heavier .

So considering the ultra light plastic frames , and the new light and happy dance on the pedals style of riding a 170 mm crank is far better for you .

hope this helps you decide .

p/s ... i finally got a new 53 tooth campy super record from the seventies so i will drop down to a 53 this spring . Considering my many industrial injuries over the years , and i am not even going to worry on if i have a 12 on that freewheel ...... omg no 12 or 11 how will i survive downhill? oh i forgot , yes steel frame , it just foats past the plastic bikes . lol .

 

[ElChingon]

dear god say it isnt so. nnnnnooooooooooooo not here please anywhere but here

Yea, time to merge it with the other thread black hole.

 

[hfer07]

My one recommendation: do not get sucked into the vortex of the short crank thread elsewhere on this forum.

+ THIS
just do what you feel more confortable with.

[Personally, I don't think you will find much difference between 170mm and 175mm cranks. Based on the results of studies, as listed below, there is no difference in maximal power with slightly shorter cranks and you will be able to reach maximal power quicker with the 170mm cranks, but because your cadence will be higher (which may be beneficial in a hilly area) with shorter cranks you may fatigue more quickly

based on what the OP wrote- I'm incline to believe he's better off opting for "spinning" rather than "pushing"- since the injury factor is the limiter- & having in mind the nerve weakness issue-you want to "stimulate" your feet & toes with movement rather than force them to work harder with the extra torque...