Negative effects of shorter cranks

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CR987
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by CR987

cyclespeed wrote:
Mon May 20, 2024 3:30 pm
CR987 wrote:
Mon May 20, 2024 2:59 pm
I don't understand the aero benefit, your seat height is higher so you're bent over more to get to the bars. This can be achieved by lowering your bars, either by removing spacers or a negative stem.
Also, the same 'research' showed plenty of benefits to oval rings (that's why so many people bought them).
Research on crank length is also inconclusive. That's why I made the comparison. Froome did ok on oval rings and Poggy is doing ok with 165's

Imagine drawing a straight line down the torso of a cyclist. Commuter will be at about 75' or 1130h on a clock. Amateur cyclist maybe 45' or 1030h on a clock.Pro cyclist maybe 30' or 10 o'clock.

As the angle drops, so your back flattens.The 'V' between your torso and your waist/legs, which traps a lot of air, starts to close. So that is all good for aero.

Raising the saddle achieves this. So does dropping the handlebar, but most pro racers already have it slammed. So raising the saddle helps flatten your back and reduce the frontal area that your torso presents to the oncoming air.
Like I said, I understand that, I can flatten my back by leaving my seat where it is and lowering my bars

X5SAE
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by X5SAE

pdlpsher1 wrote:
Mon May 20, 2024 5:09 pm
This article has some animations to show the effects of short cranks on a rider's position. The pelvic/hip rotation is key. The position changes might seem small on the animation but the 'as felt' effect on the bike is huge.

https://www.applemanbicycles.com/resour ... nk-length/
That was a good read. Much appreciated :thumbup:
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toxin
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by toxin

CR987 wrote:
Mon May 20, 2024 7:36 pm
Like I said, I understand that, I can flatten my back by leaving my seat where it is and lowering my bars
But how well does your body function then? It is a fact that closing the hip angle reduces muscle oxygenation and shorter cranks alleviate that. Shifting my position further forward along with slightly shorter cranks has helped me tremendously to function at a high percentage of my normal while in an extremely aggressive position

usr
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by usr

Sorry for posting late in the thread without having year through all the pages, but there's something I want to get off my chest whenever I see the headline:

Any disadvantage of soft shoes, if it exists, will get bigger with shorter cranks and smaller with longer cranks. If you'd try a tiny 10mm crank, a large part of your effort would get eaten by shoe flex (and at that scale, even by flesh squishiness I think!)

Personally, I guess I'm a short crank native with legs barely shorter than 100cm on regular 175 cranks. People say my pedaling is smooth, with very little movement above the legs. Not a high cadence rider, I keep finding my happy gear at 50 rpm in climbs (outside of climbs I can spin if I feel like it)

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cyclespeed
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by cyclespeed

toxin wrote:
Mon May 20, 2024 3:40 pm
Eh thats a bit overstated unless your mobility is truly awful, just being lower and redung the frontal area of your legs is generally more advantageous. That's why keeping your saddle height the same or even lowering it slightly, as tobin suggests, isn't the worst idea. Look at bigham's track position. Even ganna has relaxed his position slightly in recent years
I would argue that your torso, head and shoulders are far more important aero wise than your 2 femurs. And they are also in 'cleaner' air.

HBike
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by HBike

cyclespeed wrote:
Tue May 21, 2024 7:38 am
toxin wrote:
Mon May 20, 2024 3:40 pm
Eh thats a bit overstated unless your mobility is truly awful, just being lower and redung the frontal area of your legs is generally more advantageous. That's why keeping your saddle height the same or even lowering it slightly, as tobin suggests, isn't the worst idea. Look at bigham's track position. Even ganna has relaxed his position slightly in recent years
I would argue that your torso, head and shoulders are far more important aero wise than your 2 femurs. And they are also in 'cleaner' air.
Cd*A is important (and usually separation effects are included in a single Cd-value), so they count with their respective projected area.
However, Cd changes if inflow turbulence intensity changes and doesn't stay constant as is often assumed. There are measurements on circular cylinders (good approximation for your leg) showing that Cd first decays to a minimum around 4% turbulence intensity before rising again to higher values than the value for laminar inflow. So depending on the turbulence level the Cd value for the legs is likely increased due to not being in "cleaner air" as you call it.

EtoDemerzel
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by EtoDemerzel

cyclespeed wrote:
Tue May 21, 2024 7:38 am
toxin wrote:
Mon May 20, 2024 3:40 pm
Eh thats a bit overstated unless your mobility is truly awful, just being lower and redung the frontal area of your legs is generally more advantageous. That's why keeping your saddle height the same or even lowering it slightly, as tobin suggests, isn't the worst idea. Look at bigham's track position. Even ganna has relaxed his position slightly in recent years
I would argue that your torso, head and shoulders are far more important aero wise than your 2 femurs. And they are also in 'cleaner' air.
100%
Because from the waist up, it's the only part of your body that you can alter for, sometimes, drastic aero gains.

Unless you're willing to chop off leg muscles, anyone's legs are going to churn wind. No changing that.

toxin
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by toxin

That's why keeping your saddle height the same or even lowering it slightly, as tobin suggests, isn't the worst idea

steve028
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Joined: Thu May 23, 2024 8:21 am

by steve028

AJS914 wrote:
Tue May 05, 2020 5:53 am
That Triathlon Show just had a podcast on fitting where the fitter talks about crank length:

https://scientifictriathlon.com/tts232/

Show notes:

Firstly, what one must understand is that crank length does not affect the ability to produce power, unless we are talking about ridiculous extremes.

What happens when crank length is reduced is that the hip angle is getting more opened up and the knee doesn’t ”bump” into the stomach as much, which makes it easier to breath and also makes it more accessible to getting even lower and more aerodynamic.

So, for me going with shorter cranks is a benefit in almost all situations, and could as well help for those with knee injuries.
show notes sum that up perfect

steve028
Posts: 33
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by steve028

usr wrote:
Mon May 20, 2024 9:56 pm
Sorry for posting late in the thread without having year through all the pages, but there's something I want to get off my chest whenever I see the headline:

Any disadvantage of soft shoes, if it exists, will get bigger with shorter cranks and smaller with longer cranks. If you'd try a tiny 10mm crank, a large part of your effort would get eaten by shoe flex (and at that scale, even by flesh squishiness I think!)

Personally, I guess I'm a short crank native with legs barely shorter than 100cm on regular 175 cranks. People say my pedaling is smooth, with very little movement above the legs. Not a high cadence rider, I keep finding my happy gear at 50 rpm in climbs (outside of climbs I can spin if I feel like it)
never actually thought of that, I suppose it would also exaggerate any hip/leg imbalance too so you may notice a leg lenght descrepency more on shorter crankls and may need to address it with shims etc

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wheelbuilder
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by wheelbuilder

Norcal seemed surprised at the 170 and 175's run by VLAB in his Giro video.
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Pierre86
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by Pierre86

wheelbuilder wrote:
Fri May 31, 2024 9:07 pm
Norcal seemed surprised at the 170 and 175's run by VLAB in his Giro video.
Mostly tall riders left though, excluding Tratnik.
They also sit very forward on their bikes which is another way of opening the hips
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andy4g63
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by andy4g63

Crazy thought:
Do you guys think that the cleat placement also counts in crank length discussion?

Depending where your cleats are, all the way back or forth alsochanges the input???

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Mr.Gib
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by Mr.Gib

andy4g63 wrote:
Sat Jun 01, 2024 10:58 pm
Crazy thought:
Do you guys think that the cleat placement also counts in crank length discussion?

Depending where your cleats are, all the way back or forth alsochanges the input???
Assuming a fix ankle angle, I would think not. Saddle height and fore and aft location might be affected depending on foot angle (toe down).
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wheelsONfire
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by wheelsONfire

At what point does it affect your preferred cadence? No matter how much i ride, i can't get away from the fact that my average is around 80rpm.
I also must admit, i don't really like spinning like crazy. I can do it in short intervals, but i wouldn't want to average at +10rpm.
I went from 172.5 to 170, but i wanted 167.5mm cranks. Only option was 170mm. Not sure if i should buy a 165mm set.
It seems people here are mostly fore shorter...
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