jyl

What do you think about Zencranks?

https://www.zencranks.com/index.php?o...&id=2&Itemid=1

If I understand it, the advantage is that at the top of the stroke, say from 10 o'clock to 2 o'clock, the crank is effectively very long - 200 mm for example - giving you extra leverage. But at the bottom of the stroke, the crank is effectively normal length - 175 mm for example - so you do not lose cornering clearance.

Leonard Zinn reviewed them very positively, after a year's use. That carries some weight with me.

But I do not really understand why they work. If you have 200 mm cranks and I have 175 mm cranks, can't I just shift to a cog two teeth bigger, to get the same gain ratio?

thirdgenbird

It's not gain ratio, it is leverage. A longer lever makes it physically easier to turn a higher gear.*

*im not making a comment about the crankset, only the theory behind them

Andrew R Stewart 

There is a history of over a hundred years of claims of devices that "add power" that always end up not being so. I fail to see how these cranks increase my (repeat MY) power output. Andy.

thirdgenbird

Just wait till you try them with oval chainrings.

hairnet

Looks just like Biopace

HillRider

+1 I read the Zinn review and they didn't work any better than his own longer cranks. P.T. Barnum had it right; "There is no free lunch."

sreten

Hi,



But as Zinn pointed out they worked better than standard length
cranks for someone that suits longer than standard cranks,
without the cornering clearance issues of fitting longer cranks.

The fact that they will always hang upside down I assume
means they will always be a pain to clip into and that
might be a deal breaker for someone considering them.

The extra leg movement and the leverage it gives is not
the same as changing the gain ratio by changing gears.

rgds, sreten.

dabac

In don't understand the function, is there some internal gearing making the short arm rotate in synch with the crank?
Or is it free to swing between two positions?
The whole way round?
Is it fixed at an angle to the longer arm?

ThermionicScott 

I think someone else said that, unless you're obliquely referencing his other famous quote.

Looigi

The arm is fixed to the pedal and rotates at the crank. Nothing else. It's just a very high stack. You can achieve the same thing by putting a block under your cleat to lift the shoe off the pedal a like amount.

dabac

Ah, I see. You get the virtual lengthening of the crank by tilting your foot forward.
If you were to ride with your foot held perfectly flat it'd just be like having the bb a tad higher.

HillRider

Well, Barnum gets credit for a lot of things he probably didn't say. The reference wasn't intended to be oblique but here is a Barnum original that you probably thought of: "There's a sucker born every minute."

sreten

Hi,

Only if also at the same time for both cases you only apply force vertically on
the pedal pivot, as it is the same vectors but lifted, which of course you can't.

rgds, sreten.

You could easily modify cage pedals and toeclips to be exactly the same.

FBinNY 

I must be missing something, but to me it looks like they have everything bass ackwards.

It appears that functionally this is no different than a pedal with blocks or a thick deck, which keeps the foot higher off the spindle center.

Ask a child what it's like pedaling with blocks, or watch how their feet slip off with the pedal spinning. Of course step-in cleats make a difference but the basic issue is the same, and contrary to 100 years of trying to keep the foot closer to the spindle, or even as Shimano did sometime back below the spindle line.

Again, I might be missing something, but this just seems like another perpetual motion machine.

davidad

There is for bicycle junk!

FBinNY 

For bike junk it's more like 2 a minute.

techsensei

Do you see any professional racers using them? If it is such a great idea and legal to use, I'm pretty sure at least a few riders would want any advantage they could get. All I see on their site is that one team tested them last year.

dabac

It IS pretty much the same.
I missed it at first too, but the "claim to fame" comes from including a forward tilt of the foot into the equation, which creates the effect of a longer crank on the downstroke.

A more interesting way of doing things would have been to add a gear arrangement to the pedal/crank interface, allowing the pedal axle to walk around on a (small) circle at the end of the crank. Get the tooth count right, and you'd have the effect of a longer crank at both downstroke and upstroke.

thirdgenbird

That would be needlessly complicating it. The extra crank lenght is driven by exactly that, extra crank length. These are 190mm cranks designed for someone who traditionally uses 175s (look at the numbers on the chart) Don't look at the pivot as a way to add crank length, look at it as a way to increase pedal clearance with a longer crankset. It isnt adding length on the downstroke, it is taking it away at the bottom. Their performance should be similar to a 190mm crankset without the pedal clearance concerns and nothing more. Another solution would be longer cranks and a taller bottom bracket.

ive got no interest in this product as a performance gain, but it might be an interesting way to lower the bottom bracket on things like touring bikes or folders with smaller wheels.

FBinNY 

This is what I thought it might be. A synchronous changing of crank length based on position using a gear or cam arrangement. If it were it could put it into the category of whether the benefit warranted the mechanical loss of more moving parts. I was surprised and disappointed when I saw what it actually was, which IMO puts it into the same category as L-shaped cranks.

FBinNY 

Not true. If the foot and pedal stay horizontal throughout the stroke it doesn't in any ay change effective crank length which is fixed by the distance separating the bearings. What it does is raise the foot position at all places in the circle, exactly the way children's pedal blocks do.

The maker's claim that length changes because the foot is angled seems more complex, because there's a compound lever, but essentially is the same. However it has a major drawback of creating a pedal torque which increases stress on the foot and ankle. This is probably minor if the foot stays level and above the bearing, but increases as the foot is angled and the force is applied forward of top-dead-center.

No matter how you slice it, this is another L-shaped crank, and insults previous attempts to improve the bio-mechanics, such bio-pace, power cm and others which at least had some merit.

thirdgenbird

You said my post want true but they your evidence supported it.

with the foot horizontal it doesn't change the crank lenght (190mm) on the front of the stroke at all. This is exactly what their own diagram shows. The effective crank lenght is 190mm and the actual crank lenght is 190mm...

at the bottom of the pedal stroke (foot horizontal) the block reduces the crank length. See math on diagram.

the only "complex angle" they suggest is at the back of the stroke where it again reduces the crank lenght from 190 to about 175mm

the only difference between this, and pedal blocks is increased pedal clearance. It isn't a performance enhancer, it is a way to use longer arms 190 vs 175 without pedal strike concerns. Anything more is a gross over complication.

it shares nothing with L shaped cranks. The bb spindle to pedal distance (effective lever) is constant with an L shaped crank. These have a variable lever lenght. It matches the crank lenght on the power stroke, and it shrinks it for pedal clearance at the bottom.

FBinNY 

You're right, and I apologize. Basically we agree.

I meant to and forgot to parse the quote down to the one sentence that wasn't true, the statement that it would act similar to a 190mm crank, albeit offset higher. (since fixed). No matter how you slice it, this will still perform as a 175mm crank since the pedaling force is applied at the 175mm mark, and not beyond. I describe it as a 175mm crank with pedal blocks, nothing more or less.

thirdgenbird

You are a smart guy, I knew you would come round

Actually, it is a 190mm crank with a pedal block. The light blue is a traditional crank*, the dark blue is a Zenn crank.

Here is lennord Zenn's comments from his review of the longer (200mm version)

"At first blush, it may look to you like a 200mm Zencranks arm is equivalent to putting a block between your shoe and your cleat equal to the length of the little link attached to the pedal shaft (in this case, 20mm, although future versions for 200mm and 195mm will be 15mm) and using a 200mm crank. This is true, except for the fact that you get 20mm higher cornering clearance with the Zencranks."


* a standard crankset has a similar egg shaped pedal stroke due to the stack height of the pedal.

FBinNY 

This is the point at we disagree.

The effective length of a crank is set by the distance from the center of rotation to where the driving force is applied. As long as the offset pedal is still attached to a bearing at 175mm from the center of rotation, it's a 175mm crank. Putting blocks on the pedal doesn't change that. The key is where the bearing is located and the line of force applied through that bearing.

If you consider this to act like a 190mm crank (with or without blocks) you've accepted the seller's premise, something which I don't. Think about this a while, and maybe you'll be the one to come around this time.