thirdgenbird

Correct. It is a 190mm crank from bb to spindle. They don't even sell a 175. We both agree on the physics but you think we are talking about a 175mm crank but we are not

the 175 on the chart is comparing their 190 with a standard 175. They are selling people longer cranks than they normally ride. If you ride a 170, they sell you a 178 (their shortest size)

FBinNY 

OK, I missed that it their claims. So what we have in essence is a 190mm crank with the cornering pedal clearance of a 175mm crank. So any claims related to power are BS. I guess that if you really wanted 190mm cranks, and didn't want to coast through hard corners, or use the motorcyclists maneuver of leaning the body more than the bike, than these might make a bit of sense. But the issue of pedaling with a block will become a problem in short order if you pedal with your foot angled down.

IMO - Those tall enough to want these would be much better served with a higher BB, than this nonsense. Another alternative would be to use a Phil Centric BB mounted in the top position to raise the center of rotation without any drawbacks except the dough spent.

thirdgenbird

Ding ding ding! (My original post makes sence now doesn't it )


not surprisingly, the inventor is also apparently the guy who fit Marco Pantini. I am guessing he is the reason 5'8" Marco was seen on 180mm record crank arms. I agree that a taller bottom bracket and lower Q factor is a better solution.

the only application I could see these making sense (in a shorter version) is on a mini velo that you want to keep low for easy saddle mounting and quick handling. A touring bike may also be an application (low bb is more stable)

FBinNY 

There is no application, except for fudging a long crank (for those who want it) onto a bike while keeping the cornering angle the same.

There's no benefit in terms of saddle height, since that's based on ass-to-pedal distance, not ass-to-BB distance, so the saddle would need to be raised by the thickness of the blocks. As for touring, lower BB's are only more stable if the entire center of gravity is lower, and since the saddle has to be raised, you're back where you started. Cornering clearance also barely matters, since tourists have no reason not to coast through hard turns, and most do because they find that the straight other, helps to stabilize the bike by forming a saddle to crank brace keeping the frame and body together.

SharpCarp

Zinn's a perfectly good guy, but he understands that his job (at Veloweek) is as an industry marketing/PR rep.

dabac

I agree that whether it'd make sense in terms of efficiency or not would remain to be seen, but the biomechanics might have something going for it. You'd get a longer crank where it'll be most useful, while "only" needing the knee bend of a significantly shorter crank. It's bound to be beneficial for one medical condition or the other.

thirdgenbird

the saddle wouldn't "need" to be raised as the effective length shortens at 6 o'clock back to a standard length. You will be forced to deal with more compression at the top end however. Your saddle height may need to come up some to split the difference, but not likely the full 15mm.

Your comments about touring bikes and corning clearance are true though. I still see a mini velo as a potential use, but it is still unnessisary complexity for potentially unused cornering clearance. What little is gained may also be removed by one pedal choice that appears to hang at a bad angle for city use.

FBinNY 

This is why I keep saying I must be missing something. Discounting the effects of foot angle moving the pedal forward of TDC by varying amounts through the stroke, Zen doesn't change the diameter of the foot circle, it only moves it up with respect to the normal circle of a crank of the same length. So if you have a normal 190mm crank, and a Zen 190mm crank your foot is still traveling through a 380mm diameter circle either way.

The only ways to shrink the pedal circle and recuce the arc of flex at the knee is with a shorter crank, or by ankling, dropping the heel at the top, and extending the toes at the bottom.

thirdgenbird

Ou are missing their conversion chart. They recommend using a longer crankset but the block effectively shortens it at the bottom. The whole crank circle doesn't move up. The bottom (where saddle height is measured) stays the same. The rest moves "up an forward" on the bike. Their goal is to use a longer crankset while maintaining the distance from saddle to pedal platform at the bottom of the stroke.

dabac

The thing you're missing is that he isn't discounting the foot angle, he's built the concept around it. It's what ties the whole idea together.

FBinNY 

No, I see that, but I was responding to Dabac's reference to the benefits of a longer crank without the knee bend that such would imply. Either way you're turning a circle with a radius equal to the crank arm length, though shifted up by the height of the "block".

IMO, the folks are using a bit of sleight of hand to make theory look better. They have the circle of a 190mm Zen and that of a 175mm standard crank spinning on the same center super imposed. This correctly shows the ground clearance benefit realized, but can camouflage what the deice actually does. If you plot the foot circles of the 190mm Zen next to a plain 190mm crank, you get two nearly identical circles one higher than the other by 15mm (or whatever the block height is. There is no difference in circle diameters, just a vertical offset.

To get the benefit Dabac was referencing you'd need a system whereby the pedal were above the bearing at the bottom and below at the top, so the foot travelled a flattened oval. That would require more machinery, and where I originally thought these guys were headed, but aren't

dabac

Depends on what foot angle you're counting on. As an extreme, imagine a ballerina turned cyclist, doing the downstroke on pointe. In that scenario basically the whole block height would create a virtual crank extension for that part of the circle. Variable leverage the easy way. And a good way to create schematics for marketing by turning a circle into all kinds of interesting cam shapes by assuming different foot angles for different sections of the stroke.

thirdgenbird

foot angle doesn't tie anything together. It is needless overcomplication. The "performance gain" is due to the longer crank lenght, not foot angle.

i see where you were coming from. Yes, 190mm vs 190mm zen only raises the circle some. This is why I said performance should match a 190mm crankset. I was comparing 175 vs 190.

foot angle will slightly change the shape of the circle, but I don't believe there would be any performance gain from it.

My mind went here first too but then I realized it was just a pedal block in a different location. It is as simple as a block of wood.

FBinNY 

I see they claim that, but I consider it BS. If you plot the possible changes of foot angle against the cicle of rotation of the pedal (not crank) arm you'd find that the vertical height from TDC to even 45° forward changes only a tiny bit. (cosine of 45° = .7 x 15mm = 10mm, vs. 15mm vertical = 5mm drop/rise). So there's a drop of 5mm possible at the top or rise at the bottom if you ride toe down at that point in the circle.

This isn't very much, and unless one has very short feet, pales in comparison to the effects that ankling would provide on a simple crank.

I know that I can be very thick, and invite anyone less skeptical than myself to give these a shot f they think they make sense. OTOH having grown up in the city before there were the "scoop the poop" laws, I've gotten pretty adept at recognizing sh*t before I step in it.

thirdgenbird

FBinNY and I seem to be on the and page.

FBinNY 

I considered that and ruled it out, not because I don't know any ballerinas, but because riding toe down vertically with these would be a great way to hyper-extend and/or break one's ankle. The pedal arm isn't fixed to the crank arm the way a cheater bar would be on a wrench, so pressing down on the pedal with the bar horizontal, would have the pedal wanting to continue to arc down to be below it's pivot point, turning the it and foot attached to it upside down.

This torquing effect at the pedal platform is something we all feel every day, as the back of the pedal digs into our feet while the front doesn't. It's the reason that we've had 100 years of effort to get the the foot closer to or below the pedal's center of rotation.

dabac

I never said I believed in its effects, but I think I've figured out the theory behind the marketing.

sreten

Hi,

I think you are missing something, and that is if you assume the the foot circle is moved
up but still the same, the centre of the torque, the crank, does not move, so the two
cases are not the same. Analysis by extreme is useful, consider say 50mm lift, and
the relative torque through the crank at 1 o'clock and 5 o'clock for the two cases.

rgds, sreten.

Assume for vector analysis the angle between the extension and the crank resolves
to a straight crank directly connected to the pedal spindle, look at that length.

FBinNY 

You might draw free body diagram with force vectors in various positions.

I've no dog in the fight, and everyone is free to draw their own conclusions. As far as I'm concerned, I've made all my points and am happy to let it rest.

sreten

Hi,

Well there I go thinking you might be interested in what is actually happening.

rgds, sreten.

FBinNY 

If you read my prior posts and dialogs with others, you'll see that I've already given this more thought than it's probably worth.

thirdgenbird

Amen

DX-MAN

One word, five letters -- perfectly describes the hype around this product:

Fecal.

gregjones

Hangin' off.

Used 40 years ago when exhaust pipes ran to the side of the "then new" wide 4 cyl engines. A hard right turn and your outside tube hit pavement. Thump and you did a quick boot scoot to the left.

Hang off the saddle, hold the bike upright..............lower center of gravity and you're around the corner in style. Wearing leathers, a shot of WD-40 on the butt made things easier.

Header manufactures learned to route the tubes under the center of the motor. Then tires got better. Anymore, hangin' off is about the same as skid stops on a fixie. Looks good for the squrls (I think they call gals these days). And, please don't use the passenger pegs to get the "rear-set, Ricky Racer" look.

Off topic.

I like products to stand the test of time before I invest in them. One of my latest purchases was a pair of 105 crankarms with a JIS taper. They worked then, they work now. I don't have the power to know any better and my bike goes forward.