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PostPosted: Thu Sep 05, 2013 8:28 am 
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Check out this crank called Zencranks. Works a bit like Biopace, Rotor, O.Symetric, etc., only a bit different. Lennard Zinn appears to think they work...

http://velonews.competitor.com/2013/09/bikes-and-tech/reviews/reviewed-zencranks-pas-crankset_301441

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Posted: Thu Sep 05, 2013 8:28 am 


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PostPosted: Thu Sep 05, 2013 9:26 am 
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One interesting thing about all those nonstandard pedalling approaches is, that you have races won with all of them -- even if they are found to be suboptimal later on. Makes me think it maybe doesn't matter that much, after all, and the human musculoskeletal system can adapt to whatever the next revolutionary crank/chainring is.

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PostPosted: Thu Sep 05, 2013 10:00 am 
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I don't think this is a particularly new design. I'm sure Fairwheel used to stock an extremely similar product years ago, I vaguely recall Madcow even testing them and being fond of them.

Apologies o great Madcow if I recall incorrectly.


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PostPosted: Thu Sep 05, 2013 10:11 am 
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Aha! Some googling with phrases that sounded familiar netted me what I was after. The design appears to have been updated a bit since fairwheel stocked them but the look a whole lot more polished than the ones in the Velonews link.

http://www.vista-bikes.com/index.html


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PostPosted: Thu Sep 05, 2013 10:19 am 
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Those Vista crank look waaay better! I wonder what they cost.

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PostPosted: Thu Sep 05, 2013 4:54 pm 
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While the Vista crank uses a similar route to the Zencrank to achieve its ends (bearings in the crankarm with pedal body off center from point of pedal rotation) , they are actually diametrically opposed.

The point of the Vista Magic pedal (and other "drop" style pedals) is to put the foot in line with the pedal's point of rotation, so the pedal body/cleat is offset well BELOW the axle.

The Zencrank is using the same methods to achieve the opposite result, putting your foot well ABOVE the pedal's point of rotation, way more so than with normal pedals. It is very similar in effect to if you were to put some big honking blocks or spacers between your shoes and cleats, to raise your foot way above the pedals.

The most solid argument, IMHO, for "drop" pedals like the Vista Magic pedals is that moving the foot closer to the pedal's point of rotation reduces rocking torque, which means that you don't need to recruit your lower leg muscles as much to stabilize the foot on the pedal. This can save you energy that could then potentially be utilized for efforts that are more productive to forward propulsion rather than stabilization. That is why most shoe and pedal manufacturers are trying to reduce the thickness of the soles of their shoes and pedal bodies, as those are baby steps in the same direction. Vista has also offset the pedal body forward a bit, so it looks like you can achieve a more "forward" foot over axle position with their pedals than with a typical drop pedal (if you can call any drop pedal "typical"), which is kind of like the whole "Arch cleat/midfoot cleat" concept.

Back to the Zencranks, their argument, as far as I can figure, is that they allow you to use a longer than normal crank, without the downside of reduced pedal clearance (since the pedal body will be offset upward at the bottom of the pedal stroke). If you like the idea of longer cranks and the increases in leverage they provide, but have found that cornering clearance prevented you from trying them out, then this might be worth exploring. They don't address the presumably disadvantageous increase in rocking torque in the info on their site, and I didn't see Zinn really addressing it in his article either.

My personal take on things is that if you just want longer cranks and don't pedal a lot of tight corners, just get plain old longer cranks. If you want longer cranks but want to keep your cornering clearance at conventional crank/pedal levels, then Zencranks are worth a look, but you would need to calculate the performance gain of improved pedal clearance minus energy cost of increased rocking torque.

I should note that both Zencranks and Vista Magic seem to be making claims about their pedals providing some sort of "free lunch" scenario, and I'm just not sure I buy it. It is actually kind of funny because if you check out the diagrams/videos on each of their websites, they have very similar illustrations showing the circle traced by normal pedals vs. circle traced by their pedals, obviously they are each offset in opposite directions, but both claim increased total power.

I personally like to keep my foot as close to the pedal as possible, to reduce rocking torque, and would consider using a drop pedal if there were any that didn't cost a ton or have other disadvantages due to the technical limitations. I understand the proposed benefits of longer cranks, but remember that they increase the acute bend of the knee at the top of the pedal stroke by double the length of the increase in crank length, and I don't find that to be comfortable for my knees or beneficial for pedal fluidity. Zencranks do nothing to change the overall diameter of the circle your pedals trace, they just offset it upward, so I don't see them addressing my main issue with longer cranks.


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PostPosted: Thu Sep 05, 2013 5:23 pm 
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Essentially, these Zen cranks appear to be nothing more than long cranks with pedals that have a massive stack height, aside from not even featuring my preferred pedal system. Not to mention a wider Q-factor.

In other words, I'll pass.

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PostPosted: Thu Sep 05, 2013 6:47 pm 
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@TheKaiser: great explanation! Thanks.

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PostPosted: Thu Sep 05, 2013 9:37 pm 
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I think it is a little more complicated than simply offsetting, and is not quite the same as a pedal with a very high stack-height.

With the Zencrank system, at the top of the stroke the effective crank length is shortened by the 'stack' so there is more knee clearance. At the bottom the effective length is both the stack (pedal offset) and the crank length. At the 3 and 9 o'clock, the pedal sits below the crank there is a pythagorean effective crank length (root of crank2 + offset2) so is marginally lengthened.

As a way of getting through the so-called deadspot I can see the charm, but my preference is to build a smooth action with low stack to help through the stroke.


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PostPosted: Fri Sep 06, 2013 3:52 pm 
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@SWijland: No problem, glad that came through clearly!

@ghisallo2003: I think your logic is completely sound except that, if I understand you correctly, you seem to be describing a "drop" pedal like the Vista Magic, and the additive effect of crank length plus "stack" would be the opposite of what you say, when using the Zencrank.


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PostPosted: Fri Sep 06, 2013 9:04 pm 
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You are right - I had not factored in the locked-in pedal axle. Worse than I thought !

At the top you get extra compression so it increases the deadspot. The benefit is the higher clearance at the bottom. Not sure this is a sensible trade-off.


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PostPosted: Sat Sep 07, 2013 11:04 pm 
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Why is he testing with such long crank arms? I mean 177,5, 180, 200mm. He's a tall guy but unless you happen to be a giant..

Quote:
In all cases, I rode as hard as I could go. Of course, some days are always going to be better than others, and multiple runs are required to see any kind of a trend. [For those wondering why I didn’t use a power meter, holding a given power output (which would have had to have been measured in the hub rather than in the crank or pedal for obvious reasons) would result in the same time on the climb. Or, measuring average power output or total work done when going full out should have resulted in the same relative results on a steep climb without significant wind.]


Too right. Qualitative human power using a mechanical process is limited to interface of hardware. That's to say hardware will give reading limited to its sensor capabilities. If there is a mechanical advantage the power reading won't take into account. Mechanical measuring doesn't calculate precise internal physiological work/power expenditure. Only relative.


Quote:
On the upstroke, due to the foot pointing down, it is close to following the same trajectory as with the 180mm crank. The illustration here compares a 190mm Zencranks crankset with a 15mm link arm to a 175mm standard crank, a scaled-down version of what the 200mm with a 20mm link compared to a 180mm standard crank would look like. Because the foot comes up so high, there is an increase in the gravitational kinetic drop of the mass of the foot, leg, and pedal. Zani claims that the cost of lifting the foot that high does not counteract the gain from dropping it.


This statement is extremely dubious.


The chainwheel has the pedal attached offset to the bearing using a pivot. The bearing is in chainwheel arm.
The motion of orbital path of pedal stroke produces a trilate, not an egg shape. I have created proof of principle to show this. I used minor variables to exemplify size of pivot (which offsets the pedal).
Clearly it is seen, the trilate has a longer trajectory from 12-6 o'clock position. This is Shimano's hypothesis for power optimization at delivery. Then there is a relatively shorter up-stroke. Also dead-center is offset to part of the up-stroke leaving more for down-stroke after 12 o'clock position.
What we see overall clearance is decreased. it's like running longer chainwheels on your bike.

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Posted: Sat Sep 07, 2013 11:04 pm 


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PostPosted: Mon Sep 09, 2013 6:03 am 
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Lennard may have become fitter as the summer progressed. In my opinion, it is a shame he didn't mention how this may have affected his conclusions about the cranks.


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