So everyone has been saying that there is no appreciable loss in power going to shorter cranks
What I have heard is that you can make up for the loss of Crank torque (same force, less distance), by increasing RPM more easily, so that your foot speed is higher inversely proportional to crank reduction.
Power = FxdxRPM
But what I am finding is that my RPM (whenever I check with a 1 min count) is no different. The guys are right. My CT rides show no loss of power, in fact, it may have gone up, but it is very hard to know if 2-5W average gain might just be related to how rested I am for workouts vs not being rested.
Anyway, I’m finding it easier to apply more force on the shorter cranks (165). My theory is that the slightly shorter crank lengths puts me in a better range of motion for my muscles to contract. Arguably 165’s on me is like 175’s on someone 6 inches taller, so maybe, I’m just finally using cranks with the right propoortion to my femur and tibia lengths. Interestingly enough, when I get out of the saddle and stomp on a steep hill, that’s when I see that I can generate the most additional delta compared to 170’s.
While I don’t have a power meter to give the pocket protector crowd a lab number, I can say w/o a doubt I was much more comfortable and ‘felt’ more powerful and to that end was at least as good with my 170’s vs. 175’s. I’m 6’1", 35" inseam. I’m going to snag some 165’s when I find a good deal and see how that feels.
“so that your foot speed is higher inversely proportional to crank reduction”
It’s a nit to pick, but I want to point out that your foot speed would be faster at the same RPM. I think that you meant to say RPM rather than foot speed.
The only explanation for you seeing the same, or more, power at the same RPM is that you are applying more force to the pedal than you were with the longer cranks. And unless you have stumbled upon a mechanical efficiency change between the 2 model of cranks (ie. your old ones made of rubber) then you must have found a physiological efficiency with the shorter crank arms just as you suggested.
Complete opposite for me. I switched from 172.5 to 165 in Dec. of 2008 and found that my cadence was naturally higher at steady and easy efforts, however the max power was just not there. After riding them for about a month I felt great and was riding at 90-95 rpm as opposed to my previous 80-85 rpm. I believe this led to an increase in power output at given heart rate efforts. However, I always had problems putting out power on climbs. I recently switched out the 165 for 175 and I am loving it. My cadence natural is still 90-95. I expected to struggle to keep cadence up after the switch but this was not the case. I am seeing an increase in power on my intervals at the same heart rate and cadence, but the main difference is the increase when riding at 75-80%. My inseam is 31".
What I have heard is that you can make up for the loss of Crank torque (same force, less distance), by increasing RPM more easily, so that your foot speed is higher inversely proportional to crank reduction.
I don’t think your statement is correct…for a given rpm, your tangential foot speed will be SLOWER with a shorter crank arm. Think of it this way, your foot travels through a smaller circumference circle in the same amount of time.
So…if you want to keep your tangential foot speed the same between the 2 cranks, then the foot needs to travel through the smaller circle in a shorter amount of time, and thus the CADENCE would go up to keep the SAME foot speed. When you say your cadence is “no different”, you do realize that the expected difference in cadence between the 2 lengths would only be ~2-3 rpm, right? Also, are you sure you’re using the same gears between the 2 cases?
Now then…a 2-5W average gain is MIGHTY small to be claiming any sorts of advantages for one length or the other. But, as expected, at least you can say that switching to the 5mm shorter cranks didn’t HURT your power either.
I guess I’m trying to say I wouldn’t go imparting any magical properties (especially based on proportionality) to the crank lengths based on what you’ve written
Anyway, I’m finding it easier to apply more force on the shorter cranks (165). My theory is that the slightly shorter crank lengths puts me in a better range of motion for my muscles to contract. Arguably 165’s on me is like 175’s on someone 6 inches taller, so maybe, I’m just finally using cranks with the right propoortion to my femur and tibia lengths. Interestingly enough, when I get out of the saddle and stomp on a steep hill, that’s when I see that I can generate the most additional delta compared to 170’s.
I think you’re onto something with this observation. We’re obviously not built to apply a uniform tangential force on the crank over a 360deg range. So there exists not only a peak torque, but very likely a functional range of torque - outside of which your leg and foot are basically along for the ride. By shortening the crank to a more optimal range of motion, you’re increasing the percentage of each revolution in which you can apply significant force. For a matching cadence, a 3% loss of torque arm (going from 170 to 165) would roughly equate to 10-11 degrees of additional force-applied rotation. The shorter crank probably allows you to ramp your force profile that much earlier in the cycle.
Complete opposite for me. I switched from 172.5 to 165 in Dec. of 2008 and found that my cadence was naturally higher at steady and easy efforts, however the max power was just not there. After riding them for about a month I felt great and was riding at 90-95 rpm as opposed to my previous 80-85 rpm. I believe this led to an increase in power output at given heart rate efforts. However, I always had problems putting out power on climbs. I recently switched out the 165 for 175 and I am loving it. My cadence natural is still 90-95. I expected to struggle to keep cadence up after the switch but this was not the case. I am seeing an increase in power on my intervals at the same heart rate and cadence, but the main difference is the increase when riding at 75-80%. My inseam is 31".
Sounds like you needed lower gearing for your climbs.
Complete opposite for me. I switched from 172.5 to 165 in Dec. of 2008 and found that my cadence was naturally higher at steady and easy efforts, however the max power was just not there. After riding them for about a month I felt great and was riding at 90-95 rpm as opposed to my previous 80-85 rpm. I believe this led to an increase in power output at given heart rate efforts. However, I always had problems putting out power on climbs. I recently switched out the 165 for 175 and I am loving it. My cadence natural is still 90-95. I expected to struggle to keep cadence up after the switch but this was not the case. I am seeing an increase in power on my intervals at the same heart rate and cadence, but the main difference is the increase when riding at 75-80%. My inseam is 31".
Sounds like you needed lower gearing for your climbs.
Agreed. Crank arm length is just another way to vary gearing. Stan changed gearing with his crank arms and could have done well to do it by changing cogs.
The change in range of motion could make the difference Dev.
The longer the cranks the greater hip/knee angles your legs go through to complete one revolution.
We tend to be stronger in the degrees of leg extension closer to full extension then 90 deg of bend.
You don’t lose gear inches but if you maintain RPM I can see how power can go up…there is likely a limit…150’s may cause a loss in power for someone of your height.
A taller person may loose power at 165’s while you gain…likely need some research and testing to know what is best.
I don’t think it’s the same. Changing gearing doesn’t have any impact on the path your pedal makes or the angles at which your joints and muscles operate. Changing crank length does.
Agreed. Crank arm length is just another way to vary gearing. Stan changed gearing with his crank arms and could have done well to do it by changing cogs.
The book was written on this almost 20 years ago, so it’s a well-traveled avenue.
“I think you’re onto something with this observation. We’re obviously not built to apply a uniform tangential force on the crank over a 360deg range. So there exists not only a peak torque, but very likely a functional range of torque…”
I don’t think it’s the same. Changing gearing doesn’t have any impact on the path your pedal makes or the angles at which your joints and muscles operate. Changing crank length does.
Agreed. Crank arm length is just another way to vary gearing. Stan changed gearing with his crank arms and could have done well to do it by changing cogs.
The crank length is just one more lever in the series of “effective levers” (i.e. gearing) between the pedal and the ground.
Jim Martin showed that maximal neuromuscular power is not affected through a fairly wide range of crank lengths.
Fixed your post for you.
Tap, tap, tap…
Shouldn’t that be “rap, rap, rap…”?
Naah…I was just referring to the study you linked to on the wattage list about self-selected cadence and thought it might apply to Dev’s original post…
“Freely chosen pedalling rate during cycling represents a voluntary rhythmic movement. It is unclear to what extent this is influenced by internal (e.g. loading on the cardiopulmonary system) and external (e.g. mechanical loading) conditions. It is also unclear just how robust a voluntary motor rhythm, the freely chosen pedalling rate, actually is. The present study investigated (N = 8) whether or not the freely chosen pedalling rate during submaximal cycling was affected by separate increases in loading on the cardiopulmonary system (changed by exposure to acute simulated altitude of 3,000 m above sea level) and mechanical loading (changed by exposure to increased power output and thereby pedal force). We also investigated (N = 7) whether or not the freely chosen pedalling rate and another voluntary motor rhythm, unimanual unloaded index finger tapping rate, shared common characteristics of steadiness and individuality over a 12-week period. Results showed that the freely chosen pedalling rate was unaffected by increased loading on the cardiopulmonary system at constant mechanical loading, and vice versa. Further, the pedalling rate was steady in the longitudinal perspective (as was the tapping rate), and like tapping rate, pedalling rate was highly individual. In total this indicated that freely chosen pedalling rate primarily is a robust innate voluntary motor rhythm, likely under primary influence of central pattern generators that again are minimally affected by internal and external conditions during submaximal cycling.”
My own experience is that both my cadence and foot speed are both higher with the shorter cranks. I have 170’s on my road bike, 160’s on my TT bike. I almost never ride the TT bike except in races (probably 2-3 hours a year in training).
The first TT of the year I actually noticed that I was pedaling really fast, but didn’t worry about it. My average cadence for 10 miles was 110rpms? My self-selected cadence on my road bike for an interval of the same duration is in the high 80’s. I have no appreciable power output difference between the 2 bikes.
Normally, I pay no attention to cadence but I actually remember on the outbound leg of the TT thinking ‘why the hell am I pedaling so fast?’. Weird. The power output was what I expected, so I didn’t worry about it.
Jim Martin showed that maximal neuromuscular power is not affected through a fairly wide range of crank lengths.
Fixed your post for you.
Tap, tap, tap…
Shouldn’t that be “rap, rap, rap…”?
Naah…I was just referring to the study you linked to on the wattage list about self-selected cadence and thought it might apply to Dev’s original post…
Ah. I thought you meant that I was tapping your knuckles.
Fascinating study results to contemplate, eh? Certainly gives new meaning to the saying “tapping out a rhythm on the pedals”!
