SpedFast

That's blasphemy!!!!!

Russ Roth

Probably seeing some of the difference in running a longer crank than the rider needs but the bikes typically come with. New XS mountain bike and it came with 170mm cranks even though it can fit a 4'6" person. Even with the pedal set for good leg extension on the bottom of the stroke the knee was bending even more than 45* on the top of the stroke. 152mm crank required raising the seat some, really only raised the seat 10mm so the leg extension at the bottom wasn't ideal but the kid would still touch toes to the ground, but with the pedal sitting 18mm lower at the top of the stroke and the seat 10mm higher, it was still a good bend to the knee that wouldn't cause trouble.
Some compensation can be made for the too long crank by spinning more since pedaling harder puts a definite strain on the knee at the start of the down stroke when the crank is too long. Though faster spinning can run into a lactic acid buildup at the knee that hurts too but probably some of the riding difference you're seeing based on height as a taller rider can just power along with the right height.

burnthesheep

Bolded = no.

The observations the person posted and you replied to aren't eyeball measurable just cruising along and seeing people ride. Maybe a lifelong fitter could eyeball it, otherwise it's really just interesting but useless conjecture without measuring the person/bike/cadence.

A longer crank in the same gear requires LESS torque over a longer distance: d = pi*dia, pi * 2*172.5mm > pi * 2*165mm. T = f/d. d1>d2 but F is equal......so T1 is smaller than T2 on the longer crank.

Next.......Crank length is not gearing. Use gearing to regulate power demand, cadence, and speed. For pleasure and fitness riders that aren't doing weird fit tricks with a tri or TT bike, the crank is a fit coordinate. Height, upper leg length, lower leg length, foot size/length. One can simply change gears to regulate the torque and cadence as they please. Also even though you "feel" you're spinning faster or slower on long and short cranks, you're not. The gear ratio is the same. Your foot just travels a different distance around the circle at a different torque.

Short cranks on a TT bike is still mostly a fit thing also, despite often being quoted otherwise. Crank length changes work on hip angle. I say still a fit thing as you can go to short cranks and have a crap bike fit wrt where you're applying force to the pedals relative to your saddle setback, height, and cleat positions.

Russ Roth

Don't know what you mean by can't be seen, the effect of too long a crank is very easy to observe when seat height is right for a proper extension at the bottom of the stroke. The rest of your rambling assumes that two riders are using the exact same gear, something neither the op or I suggested. Keeping kids racing I'm well versed with the concept of crank length and how to fit bike, years of selling high end road bikes and doing fitting with them helps. Bikes often come with poor crank lengths at the small end of rider size and riders compensate by how they ride.

burnthesheep

Out in public? The poster said outside in the wild. So unless the crank is literally well over an inch too long/short.......I call BS. And I don't mean from photo on the internet of a person outdoors taken close. I mean actually seeing folks randomly ride by.

I just looked up a women's fit chart for some Liv bikes, two cranks offered. 160 and 165. Men's in the same bike model runs 165 to 175 from smallest to largest offered. Women's is 5mm difference and men's is 10mm. 10mm is a 1/4". You can really see a 3/8" or even less than 1/4" at the "right seat height".

Sorry, no way unless the person is riding a fitting rig indoors right in front of you.

I'd put money on 95% of the time you "notice" this in public, the person has the saddle set at a really really really wrong height or the person is riding a bike that's entirely the wrong size. Yes, some bikes generically toss cranks in the common sizes on smaller/larger sizes........but what I gather here you'd need someone riding a small framed bike with an XL framed bike's crankset. Like putting a 175 on a women's s/m sized frame. Or I'm a guy and wanted to take the dog for a ride in the basket so just hop on my wife's bike instead. Yeah, you can notice that.

For kid bikes falling under the "BSO's" umbrella, yeah, maybe notice that also as some are awful. But for the right frameset size and just 2.5mm or even 5mm of crankset error, c'mon. This is a stretch.

For the wiseguy's, comprise a table guessing each of these cranks.........not all of them being triathletes run a 165.....have fun: this super slomo video would be gift for this guessing game and I still bet you wouldn't be able to tell who does and doesn't run a 165.

ussprinceton

go to your LBS and see what they say

rsbob 

May the cycling gods have mercy on your soul.

grant40

I tried it a couple of times and it hurts your feet and your behind after only a few miles.

livedarklions

I think it's also complete nonsense.

BikingViking793 

The back of my knees hurt when saddle is too high.

Garfield Cat

Pedaling technique is part of the problem. Just think of the saddle positioning, fore and aft, height etc. They're all related to the pedaling. Then the rider's ability to recruit the muscles to support the torso, another fore and aft saddle positioning. The dynamics go crazy when you think about it. Cycling is making the body adjust to the activity...being on a bike.

The question: what sportive activity is less dependent (compensatory) to a mechanical device? And don't say sex.

JehD

I set my seat for leg extension. My feet barely touch the ground on whatever bike im riding.

SoulAmazing

Some laughs in here enjoyed those. To those who came to this thread to find answers .. listen to your body.

livedarklions

This is absurd, you've turned the obvious on its head--bicycles are machines built to suit our legs' natural motions. The machines are adapted to us, not the other way around. I'm pretty good on a bike, but I really can't do significant amounts of running without screwing up my feet and ankles. The bicycle machine allows me to do way more with alternating the positions of my legs than I can do without the mechanical adaptation.
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SoulAmazing

This is the first time I hear the bicycle was not fitted specifically to our body movements.

Post above hit it on the head
With a fractured ankle back 10 years ago i reach a certain limit much faster running than on the bike . And our bodies are meant to walk lol

Also what about the leg press machine at the gym. Similar movement on the bike just with both feet at the same time.

Calsun

More tiring to have the seat too low but more prone to injury with overstretched ligaments with it too high. HIking is vastly different as all your weight is supported by your body. On a bicycle people use 85% less energy to move as their weight is supported by the bike.

For me it has always been much harder on my legs to go down a steep hill than it was to go up it as my body needs to decelerate with every step. With knee pain it has often been the use of lighter duty boots that provide less lateral support for my feet and put more lateral stress on my knees.

With a new bike I do a 20 minute warmup and then adjust the height of the seat, starting out high and gradually lowering it 1/8 inch each time. When I get to where there is no lateral movement of my hips as I pedal the height is right for me. The fore and aft setting is also important and as I move the seat up I am also moving its relative position horizontally backward as well.

surak

Why would anyone on a conventional bike need to stand on their tip-toes at rest?

caloso

It is amazing to me how many riders seem to have never been taught (or figured out) to straddle the top bar when stopped. (Here's a bonus: It makes starting again much easier too!)