PeteHski

You totally lack any credibility.

PeteHski

I agree with this. 170s are inherently easier to spin faster simply because of the smaller circle. But like you I tend to notice leg extension with saddle height the most.

Trakhak

Lots of people come in hot but eventually run into posters who very obviously know more about a given topic than they do. The smart ones settle down. Most of the others continue to embarrass themselves and/or are eventually banned.

Some come back as sock puppets, of course.

Germany_chris

I thought we settled this debate years ago, short cranks allow you to get into a more aero position because of leg to hip angles and it opend your stomach somewhat..

I still like my longer cranks with my little short legs because they feel right and I'm not trying to go fast

PeteHski

Yeah, but since when did any debate ever get settled here on BF?

sir_crash_alot

If the Internet more generally ever solved a single debate, then I haven't found it yet.
(unless the debate is whether the Internet can solve debates, in which case the answer is no, no it cannot).

Turnin_Wrenches

I'm so happy to see a vibrant dialog about crank length!!! It's one of my favorite topics.

There are obviously some strong beliefs about the topic as it relates to power output. Personally, I think that part of the discussion is little more than an academic exercise leading to nowhere.

Your power is not a function of crank length alone. And I know most people involved in this discussion are aware of this fact. However, the discussion of crank length is always dominated by comments about power output that lead the less informed to believe that the two are intimately linked (which they are not). Yes, there is a relationship. The impact of crank length is not nothing as it pertains to power output, it's just not everything.

Longer cranks absolutely offer more leverage through the power portion of the pedal stroke. This add'l leverage can contribute to increased power output. It can also cause knee problems and hip impingement issues. How much power are you putting out relative to your FTP when you are uncomfortable and in pain? Whatever it is, it's not as much power as you would be putting out if you were more "comfortable" on the bike, which leads to my main point. COMFORT = SPEED

Crank length is an important element of a bike fit. Your comfort on the bike and your efficiency / output is partly a function of crank length. I'm 5'6" with a 29.5" inseam and I have a functional leg length discrepancy. The 170mm cranks that come standard on 50cm - 52cm frames put added stress on my knees and do not allow my hips to remain more open throughout the pedal stroke. I guarantee I am faster for much longer with my 160mm cranks because I have less stress on my knees, my hip angle can open up, and as a result I am more comfortable.

And when I use the term "comfortable", I'm not talking about the type of comfort you feel lying on the couch. "Comfortable" for purposes of this discussion means "your ability to hold your position on the bike". For example, the "raciest", most aggressive setup on your beloved sub-6.8kg road bike with a 4" drop from handlebars to saddle will not make you fast if you can't hold the position. It's the same with crank length.

Lastly, I think context is very important as it pertains to crank length and which crank length might be "best" for you. If you are a pure sprinter you might want to compromise some comfort to be faster at the finish. Longer cranks can help with that. For just about everyone else you should be riding a crank length that is kind to your knees and to your hips. A low stack, long reach and long crank arms are not doing you any favors if the discomfort forces you up onto the hoods because you can't hold the position.

PeteHski

Do you know of any studies showing that longer cranks actually do improve sprint power?

Turnin_Wrenches

Longer cranks improve leverage, hence increased sprint power. Do they help over longer distances? It depends.

If you're solely concerned with sprint power, then "go long" (relatively speaking) with respect to crank length. If you're more of a long-distance cyclist then shorter cranks (relatively speaking) will provide greater benefit.

Turnin_Wrenches

I see lots of requests for data and studies showing the benefit of "this or that", but please keep in mind that many cycling studies are flawed. They typically don't have an adequate sample size and/or a broad spectrum of riders (with respect to abilities). As a result, the value of the output / conclusions to the average rider is uncertain.

For 99.9% of riders a crank length of +/- 10mm will not make a "hill of beans" difference, especially if you're just doing typical 20-40 mile club rides. Most people unconsciously compensate for less-than-ideal bike fit, thus hiding problems because the distances they ride are too short. For example, if your stem is 10mm too long you may not experience any discomfort if your long rides are only 30-40 miles. Go out and do a century ride and that longer stem may not be as comfy as you thought. The same applies to crank length.

terrymorse 

I’ll take a flawed scientific study over unsupported, annonymous opinion every day. And twice on race day.

PeteHski

Increased leverage from a longer crank increases torque, but also reduces cadence. Both are equally important in generating power. All the studies I've seen show a very weak link between maximal power, crank length and leg length. +/- 10 mm is certainly in the noise regarding power. For pure sprinters it is far more important to have the right gear ratio, which dwarfs crank length as a factor.

Trakhak

Biomechanics aside, crank arm length should be evaluated as just one more factor in determining the effective gear ratio/development, one that is no more or less important than tire/wheel diameter, chainring tooth count, and sprocket tooth count. All of those factors together determine how far the bike travels for a given amount of pedal movement. For bikes with multiple gears, leverage is leverage.

Sheldon Brown, as with so many frequently misunderstood topics, offers a common-sense solution; in this case, he solves the problem of assessing the effect of crank arm length on pedaling efficiency by incorporating it into an equation.

Gain Ratios--A New Way to Designate Bicycle Gears

Reiterating for emphasis: note that he treats crank length as just one more factor in the calculation rather than as a factor that is extrinsic to the calculation.

So if you think a longer crank arm gives you more leverage for a given gear ratio, you're right. But all that means is that your foot travels farther for the same distance traveled, same as using a lower gear. As Sheldon's calculation shows, using a slightly larger rear sprocket or slightly smaller front chainring has exactly---exactly!---the same effect.

PeteHski

Exactly and the studies looking into the biomechanics have all concluded that power and efficiency is not significantly affected by crank length and especially not in the range of practical crank lengths available. Leading bike fitters (working both with pro athletes and ordinary riders) are generally advocating shorter crank lengths for almost all of their clients.

Here are a couple of articles that summarise the effects of crank length. I haven't seen any compelling evidence to the contrary, although the forums are full of personal anecdote and misunderstanding of the physics.

This article has comments from Phil Burt and Phil Cavell who are both vastly experienced.

https://road.cc/content/feature/are-...ur-bike-295963

I also like this article for a clear summary of the recent study data.

https://www.pinkbike.com/news/why-sh...o-science.html

And finally this one for looking at crank length for taller riders.

https://www.pinkbike.com/news/tested...20leg%20length.

Camilo

Why would anyone set saddle height to the bottom bracket and not the pedals? Doesn't it go without saying that it should be set to the pedals?

Trakhak

Confusion between sizing and fitting would be my guess.

PeteHski

The BB is simply a more convenient reference point when measuring and adjusting your saddle height. You just need to be mindful if you ever change your crank length or pedal/shoe stack.

If you change crank length, you may or may not want to adjust your saddle height relative to the BB, depending on your preference in balancing leg extension vs compression. Especially when moving to shorter cranks, where both leg extension and compression are reduced.

Most people set their saddle height based on their maximum comfortable leg extension (leg still slightly bent). But I’ve found that I can go at least 10 mm lower than that point without any loss of power. So I usually set my saddle about 5 mm lower than what I could still comfortably pedal ie I have about 5 mm reserve of comfortable leg extension. I find this more than enough to avoid any need to adjust saddle height (relative to the BB) when going from 172.5 to 175 mm cranks on my 2 road bikes. On the shorter cranks I just have slightly less leg extension and compression in equal measure.

Turnin_Wrenches

As a bicycle mechanic I experience this dynamic everyday... customers putting way too much faith in flawed science and info they've found on the internet. If you believe these flawed studies provide enough helpful info to make informed decisions about your bike setup then who am I to argue?

Now being a bicycle mechanic certainly does not qualify me as having any kind of expertise about the science behind crank length. But, I spend an awful lot of time around bikes, I have a decent amount of knowledge about the principles and practices of bike fit, and I have ridden my bikes many 10s of thousands of miles. I also have a significant amount of formal research training, I know a thing or two about statistics and statistical modeling, and I have worked professionally designing and performing research studies.

From my perspective, the findings from any study that has inherrent design flaws is unreliable at best. And I don't want to be making decisions based on unreliable info, especially on race day. In fact, if I'm contemplating any changes whatsoever on race day then I have clearly failed in my preparation for race day.

PeteHski

FWIW I agree with pretty much all of what you said in your earlier post apart from the bit about sprinters inherently producing more power with longer cranks. With the exception of a standing start sprint on a fixed gear bike, it doesn’t stand up to either the physics or any of the numerous studies - however flawed they may be. That’s why I asked if you had any evidence to back up your claim (more leverage doesn’t cut it for me).

When guys like Phil Burt say that crank length doesn’t affect sprint power or efficiency then it is likely to be true as those guys will have tested it extensively. The physics also backs up their findings ie. increased crank leverage is cancelled out by the larger pedalling circle. All it affects is your effective gear ratio i.e. pedal force and the distance your foot moves at a given power output.

So as you rightly say, choice of crank length really comes down to comfort and range of leg motion. As long as you don’t exceed your range of motion then crank length doesn’t really matter in terms of power or efficiency. If In doubt then shorter cranks are the way to go, even for tall riders.

The Chemist

I have the same 170mm crankset on both of my bikes, and it feels perfectly fine even on long 300+km rides. I'm of the opinion that if it ain't broke, don't fix it, so I have no desire to fool around with crank arm length at this point. I'm 178cm tall.

Turnin_Wrenches

I'm totally with you when you say it's all about your effective gear ratio as the main focus. Crank length is just one piece of the puzzle that contributes to that goal.

As for the leverage issue I agree with you, but I don't . On the one hand, you acknowledge that a longer crank exerts more leverage, so we agree on that. But you go on to say that the leverage of the longer crank is canceled out by the larger pedaling circle, which I somewhat agree with. Yes, the rider with the shorter crank arms can use a faster cadence or a harder gear or just put out more power to "compensate" for the shorter cranks. But it seems that any way you slice it, we both are saying that for the same distance traveled within the pedal stroke the longer cranks will provide more leverage and hence more output for the same level of input. In other words, it's simply mechanical advantage. That is not the same as saying longer cranks make you more powerful on the bike or that they increase your FTP or that they increase your peak power output. I'm not saying any of that. What I am saying is that the additional leverage of longer cranks allows a rider to get up to speed faster than someone on shorter cranks (assuming both riders are applying the same power to the pedals). So if you're a sprinter I say ride the longest cranks you can without making any big compromises regarding fit and function on the bike.

For everyone else, I agree with you that longer crank lengths provide no advantage. Crank length just becomes a function of fit, and shorter seems to often be the better choice. I'm a big fan of short(er) cranks.

Trakhak

Again, look at Sheldon Brown's equation for calculating the effective gear ratio (the equation that incorporates the number of teeth on the front, the number of teeth on the back, and crank length). It's easy to be fooled into thinking that the crank length represents a special factor that somehow trumps the sprocket and chainring sizes, but it isn't and doesn't. That's why it's treated as just another of those three numbers in the equation.

Think of it this way. The crank arm is a lever. But at the points of engagement, both the sprocket and the chainring are, precisely, levers, no different from the crank arm. They don't look like it, but they are.

If still you don't get that, never mind.

PeteHski

The guy with the shorter cranks is effectively riding a harder gear. He has less leverage, but also less foot travel per crank revolution. So he requires a higher pedal force at a lower pedal speed for the same cadence and power. Agreed?

So if we now compensate for the shorter cranks with a slightly lower gear (not a higher gear as you stated), the pedal force is reduced and the pedal speed is increased for the same power. Agreed?

The part of your post I highlighted in bold is misleading. If the rider with shorter cranks uses a faster cadence (not to be confused with pedal speed) or uses a higher gear at the same cadence then he is simply applying more power, which is independent of crank length.

Back to sprinters, one of those studies actually found that shorter cranks allowed the riders to reach their peak power slightly quicker, although I haven’t read that study in detail. But do pro sprinters actually tend to use longer cranks? From what I’ve read they don’t. Phil Burt talks about the GB track cyclists moving to shorter cranks (165) and Mark Cavendish is on 170 cranks, which seems pretty average for his height.

Anyway I think we both agree that crank length in the usual available range is all about fit and comfort, while inherent power is unaffected. Leverage is just a trade-off of force vs travel.

Jack Tone 

Right, as are the wheel and tire.

Turnin_Wrenches

OK, one last attempt ... WE AGREE ... I have not and am not saying that crank length is some special factor that trumps sprocket and chainring size. It doesn't.

What I have said and what I will continue to say is that all other factors being equal (i.e. sprockets and chainrings) a longer crank (e.g. a longer lever) will provide more mechanical leverage compared to a shorter one.

And if you still don't get that, then never mind .