Not necessarily more power, but the same or near same power more efficiently. And they dont require more RPM's, but they allow you to ride at higher RPM's. What they do is open up the hip angle, and in most cases this allows a more efficient position aerodynamically.

And as with most changes, you need to train them. IF you pedal at 60 RPM's normally and then up to 95, it is going to feel awful and wonky. But if you train at 90+ for a month or two, completely different feeling from the initial one, especially if you made a gradual increase over the time..

Different crank lengths will change your body position and hip angle which can effect your ability to produce power in the top of the pedal stroke. It might also affect aerodynamics due to different bodyposition.

300w is still 300w and it won't make a difference what length your crank arm and since you have gears you simple choose a comfortable cadence. If that is higher or lower than before shouldn't matter.

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Yes, as noted above the power output is still the power output but shorter cranks very generally will allow a lower body position and more open hip angle. IF, a big IF is if your hip angle is a limiting factor in your position. If your knees are bumping your chest then obviously shorter cranks will help.

My personal theory is that cranks are too long for almost everyone as a legacy of old school gearing. A short 5'6" guy like me is probably better off on 160mm or shorter than 170mm, yet every single 52/Small size bike comes stock with 170's. Why is this? Well until very recently the standard gearing on bikes was 53/39 and 12/25, the smallest ratio being ~1:1.5. Nowadays road bikes come stock with ~1:1 gear ratios (like 50/32 on a 11/32 cassette). In those big old school gears the cadence was so low and the torque so high that you needed the biggest lever arm you could get, so the shift was longer crankarms to reduce the actual force required on the pedal. Now that you can spin up climbs at higher cadences the torque value is less and the crank length can be reduced while keeping similar pedaling forces. The long cranks are a legacy item that people are accustomed to, but probably not the best option for most people.

On the road and track I am consistently slower with 160's and I'm 5'3" with short legs. 155's are a complete disaster.

The blanket statement about nobody losing power is complete BS. I spent years adapting my body to put power over the top of the pedal stroke and having a tight hip angle because I had to. Without that tight hip angle I'm unable to replicate the same power as I do on 165's or 170's no matter where I put my saddle.

You may think, just lower the saddle to get a tighter hip angle. If I do that then I don't get full leg extension -- which equals lower power.
You may also think, move the saddle forward. Nope, then I can't start the pedal stroke as early.
Another thought: just pedal faster -- well I can pedal efficiently from 70 rpm to 125 rpm (because of the fixed gear track racing I peak out near 145 rpm). I'm consistently slower using the shorter cranks.

Edit: not picking on you, you just happen to be the last poster before I saw this.

The primary pros of short cranks are reduced range of motion, reduced torque through the joints, and more space between the thigh and torso at the top of the pedal stroke. While more of a general fitting tool and not necessarily a power producing tool, more power can be unlocked if that thigh to torso angle was compromised prior to the crank change.

I'm going to state this differently. Most riders throughout the height spectrum can probably adapt to shorter cranks without penalty. Some riders have their hip angles as a limiting factor, and these riders will clearly benefit. Basically, if we were drawing a blank slate, we would probably want to spec shorter cranks for most sizes just to make the fit more flexible. That's how I'd interpret the status quo.

That's what I think, anyway - do we know that *most* riders would benefit from a more open hip angle? As in, not just could adapt to a more open hip angle, but would actually see a physical benefit? Your opening para says IF your hip angle is a limiting factor, which implies that you also don't think that the majority of riders are so limited. Or does it? I don't, I think.

There's two distinct things going on with the hip angle. Moving to shorter cranks reduces the maximum hip angle by X degrees. Biomechanally there's reason to think this may be better. But another more practical thing is that you can now lower the front end of the bike and keep the original maximum hip angle that you had with longer cranks. It's almost always more aero to have a more horizontal back.

Excellent explanation-appreciate

The longer a crank the less force to move it, but to has a higher velocity to make the revolution, and most of all the knee and leg have to come up higher over the top and lower at the bottom.

Power is not controlled but the length but the force applies and velocity which can be any mix dependent on load on the end of the crank , rpm.

Why some like short cranks , lower knee and slower circle velocity ( leg speed) .

Longer crank people usually spin faster as the same wt applied to a longer leave has a high velocity. But you can always gear up and stop that from happening too.

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Technique will always last longer then energy production. Improve biomechanics, improve performance.
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Good example of correct physics but wrong conclusion. Reminds me of the sports scientist podcaster that claims running on flat road has no mechanical power going on and means zero work.
"Strength" riders, use low cadence, choose longer cranks and use broad muscle groups at more angles of the stroke cycle (especially glutes and calves at the 12 o'clock). Their feet move SLOWER - because the cadence is lower and ride style smoother. These guys normally have the saddle further back and have their torso higher. many triathletes also gravitate to strength riding when going uphill by shuffling backwards in the saddle.
"Spinner" riders treat the chainring as a flywheel and twitch their thighs up and down with a smaller range of hip and ankle motion. They could benefit from short cranks. These guys are typically further forward over the BB and have less glute and calf activation.
As a low, aero position that doesn't tire out your posterior chain is beneficial for overall long-course performance, shorter cranks (--> spinning) might improve ironman/70.3 performance in most people, in the short term. But only in the same way as if you suddenly only did all your run training on a track with super shoes.

Good example of phenotyping that doesn't stand up to scrutiny. (Sorry, I had to start it the same way).

It's perfectly possible that a "strength" and "spinner" riders have the exact same leg speed. 2pi*(crank length)*rpm=leg speed. 100rpm on a 160mm crankset=100.5m/min. 92rpm on a 175mm crankset=101.1m/min.

FWIW I don't disagree with the saddle position in relation to cadence, that's pretty well established.

But there's no reason to think that using shorter cranks is a fleeting gain that will only apply in the short term. The aero benefits don't degrade with time. Having 'less glute and calf activation' is a mushy term. If you're going to race in a hip-forward, short crank, high rpm style then it's beneficial to train in that style. I don't buy the argument is that people should train on long cranks as a "strength" cyclist even if they plan to race a a "spinner". Train the way you plan to race, and race the way that gets you the most efficient power output.

You are assuming all humans pedal and work the same rather than just the physics side of it. You’re added to many individual body length issues and variable vs just what happens with crank length.

In a fixed gear bike a long crank will have less load and more velocity for the same power as a short crank which would have a higher force and less velocity for the same power.

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Technique will always last longer then energy production. Improve biomechanics, improve performance.
http://Www.anthonytoth.ca, triathletetoth@twitter

I wonder how much of this - who benefits most from going to shorter cranks - has to due with the ratio between femur and tibia lengths.


Those with longer tibias will tend to lift the femur higher up as they come over top dead center and will get the greatest hip impingement. Those with longer femurs can tolerate longer cranks because their femur doesn't move as much up and down at the hip.

Thoughts?

Some other points to think about with crank length: https://forum.slowtwitch.com/...milesthedog#p8024637

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