AnthonyG

Sure, and its true when cranks really are TOO long for the rider. I'm not going down the road however of putting riders who have long legs and are comfortable with 175mm cranks on 145mm cranks.

You do get to a point with short cranks that you don't feel that you are stretching your legs enough. I went all the way down to 110mm cranks to get to that point but at last I found some cranks that were too SHORT for best performance. Now honestly, I am WAY more comfortable using 110mm cranks over 170mm cranks and if they were the ONLY 2 choices I would use 110mm. Ideally I want 130mm cranks but I'm OK with 125-135mm cranks.

Anyway, I think the real advantage of short cranks is aerodynamics and comfort and I don't feel the need to argue with naysayers about power. The aerodynamic and comfort advantages are EASY to describe and demonstrate.

Anthony

Leisesturm

If you spin faster in the same gear using shorter cranks its because you want to. To prove your point. What it actually means is that you could have done the same thing with the longer cranks. Jan may have done even better with even longer cranks.... think about that for a minute. There is nothing magic about a 53 x 11 combination except that that is about the maximum gear that a cyclist can spin with 175mm cranks. They would definitely be able to handle 53 x 9 with 190mm cranks and with enough training could get nearly as smooth a cadence as they do with 170mm. But the aerodynamic resistance would also increase, faster in fact than the gains in efficiency from the bigger gear. Zero sum.

Leisesturm

A cyclist short enough to find 130mm cranks interesting is also short enough so that 170mm cranks will NOT cause their knees to hit their chests the way a taller riders knees would. Speaking of knees, the shorter crank represents a shorter lever to act on the forces presented by the combination of drivetrain ratio and wheel size. For the same gear, the forces at the cyclists knee will increase as the crank gets shorter. Period! Simple Archimedian physics. Nothing about the cyclists body structure can change this. Tendons, cartilage, and ligaments differ in their capacity for abuse, but I can wonder aloud about the long term viability of using the same gears as cyclists using "normal" length cranks when one has, for whatever reason, chosen to adopt significantly shorter ones. I for one strongly suspect that the riders using short cranks instinctively stay in lower gears except when the usual opportunities to use bigger gears present themselves: tailwinds, down-grades, drafting tractor trailer rigs... what that means in the real world, is that these cyclists are slower than other cyclists and therefore not as much fun to ride with.

McBTC

The same RPMs with longer cranks requires greater foot speed so, you cannot necessarily do the same thing with longer cranks... which is why some find that decreasing crank length results in higher RPMs without an increase in foot speed.

Leisesturm

Who says you need the same RPM's? I didn't. And you don't. That is the advantage of bigger gears. You get the same speed for less RPM's. It's why gears were invented in the first place. I strongly suspect the only reason why really long cranks aren't in wider use is the fact that pedal strike in turns becomes a real possibility.

noglider 

I agree but I wonder: does it damage our knees more or less or the same when maximum pressure is achieved with the knees up towards the chest or when our legs are not terribly bent? In other words, does the range of motion affect the wear on our knees? I really don't know, and I wonder if it has been studied. Reading this thread makes me think that shorter cranks might be good for me. I've done a small amount of experimentation, and that has strengthened my theory, but I don't claim to know for sure.

I don't see any evidence of this, and I tend to doubt it. You can convince me if you have some evidence, even anecdotal.

McBTC

Based on the what little research does exist, this writer (see below) seems to me to present a fair conclusion based on the evidence and personal experience and... I appreciate the attempt to explain with numbers what is happening on the road (or, on the trainer)-- aerodynamics and ergonomics aside, it all boils down to foot speed:




https://spokeydokeyblog.com/2015/09/...th-foot-speed/

McBTC

The Macdermid Study (2010) indicates otherwise --e.g., it took 28% less time to reach maximum power on 170mm cranks compared to 175mm cranks. (see, Ibid.)

McBTC

Logically (see link above) it does matter--e.g.,







The logic employed by the writer is particularly effective in dispelling the myth of longer cranks being superior because they provide more leverage --e.g.,

noglider 

Ah, and now you point out that there is a trade-off between creating maximum power and preserving your knees for the long term. The most efficient way to ride is in high gear at low rpm. There are good reasons we are told not to do that, and one of them is the longevity of our knees. Pursuit of maximum power can be a misguided effort for some.

McBTC

Not if, according to Martin's study, using 145mm cranks resulted in maximum power and based on the above discussion, the use of shorter cranks saves knees because they are less bent coming over the top, which probably is why in "Gist of..." above, the writer says it makes better sense to always go too small rather than too long.

noglider 

A very good point. I just want to point out that power measurements are valuable in this study, but it shouldn't end there.

McBTC

I would like to better understand what apparently is being talked about when the issue is brought up that, whatever added power you might expect to generate on the down-stroke due to having longer a longer crank is more than offset by the added difficulty of getting the other leg out of the way... which apparently is only something that can be seen with more modern equipment that measures what is going on with each leg independently and is said to support the idea of going to shorter cranks to maximize power.

Carbonfiberboy 

Very simple to demonstrate for yourself: Get on your trainer or rollers and do 2 minutes of one-legged pedaling. If you're not used to it or have what might be described as not a great pedal stroke, you won't be able to complete the 2 minutes without your drive chain going slack near the top of the backstroke. Obviously with shorter cranks it's not such a high lift over the top, so a smaller, easier contraction of the hip flexors.

OTOH, training fixes everything. One adapts to equipment, whatever it might be, from long oars to long cranks, by training.

On the 3rd hand, pedaling out of the saddle is a body-weight activity. It's pretty hard to see how shorter cranks improve comfort or power out of the saddle. The longer the cranks, the more torque. I've yet to hear anyone address this.

McBTC

Probably because dancing on the pedals is not as efficient as sitting.

bikebreak

If there weren't some gains to be had by standing in some situations I suspect the pros and their trainers would have figured that out already. I would guess that is most situations sit and spin is more efficient, but stand and hammer has it's place.


FWIW I used 170mm cranks for 4 years (with some rare use of 172), tried 165 for 4 months and found it quite lacking while standing. Finally found 167.5 arms and they are very nice.

ThermionicScott 

That's what I've been trying to get at. If you just look at lab studies, you'll conclude that sitting and spinning, and NEVER pulling up on your pedals are the only way to go. Sure, from a maximal power or efficiency standpoint those might be reasonable conclusions, but there are often real-world reasons to do otherwise.

This has been a good discussion, though.

McBTC

Still, standing on the pedals doesn't seem a lot different to me than climbing stairs and 175mm cranks would be like doing 13.8" stairs instead the 7" stair height we commonly see, which by similar logic corresponds to a crank length of ~89mm so, there's a lot of room for experimentation-- especially when you consider that even LA says he likes to stand on the pedals to get off his sit-bones for a bit, stretch the legs and hammer out of corners in a race and riders' cadence is a lot less standing than when sitting.

ThermionicScott 

And as I mentioned earlier, taking stairs two-at-a-time is faster and more comfortable for some of us.

noglider 

It is for me, which is weird. I can't stand taking them one at a time. It always has to be two. Yet I'm very short-legged for my height. I can't explain it.

McBTC

2 stairs at a time going downstairs as well...?

chelvel

Good point! It's all about step height preference. Wait! We can have no steps on incline and play with incline angle. And measure and get statistics. Here my thought stops. PS. Two-at-a-time is my style.

McBTC

But, how many steps can you climb at a time while sitting down?

ThermionicScott 

You're the one who keeps bring the stair analogy into it, don't blame us when it breaks down.

McBTC

I'm beginning to see the shortcomings of the analogy given that the typical staircase is steeper than the grade experienced on a bicycle. As it turns out, a 32% (17.7°) grade would make your ride fall among the world's steepest streets. The stairs of a typical house have a 60% grade.

I know there is a point where depending on the gearing some cyclists may find themselves in a situation where walking a bike up the hill may be their only option. I've been in that situation because I knew of such hills and purposefully sought them out to put the gearing of triple-ring setups to the limit. And, off-roading can get gnarly. I can't think of any of those situations where standing on the pedals saved the day over having gears that were low enough to get the job done.

So personally, I discount the role of standing on the pedals in cycling. That's just my likes and riding style. But as a result, standing on the pedals doesn't play a role for me in trying to understand the most efficient crank length.

In addition to that, I don't see stair-climbing as involving the same sort of circular motion where foot speeds vary depending on the arc described by the foot when holding rpms constant.