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Summary

Loving someone is giving them the power to break your heart but trusting them not to.
— Julianne Moore

A Moment In Time

(Andronymous (a.k.a. Andrew Bedno) mixes it up Hey! Bike Shop Guy (a.k.a. notoriousDUG)

Divvy Gear Ratios
Posted by Andronymous on April 24, 2014 at 11:28am

Something to think about.

Something to think about.

Does anyone know *exactly* the gearing ratios in a Divvy?
I’m trying to spec a single speed for a friend for whom Divvy’s 3rd gear is a good reference point for just a bit too easy, whereas my fixie’s a bit too hard. So I know the upper bound is 44:17(2.58) but I don’t want to guess Divvy’s.
Also I’ve also often heard (and told) the story that Divvy’s first gear is so low that to experienced cyclists it feels like the chain’s fallen off, so I’m wondering exactly how low that is.
Anyone with Divvy maintenance experience got the specs? Either the three ratios, or the teeth counts would be nice. I’d also welcome weight and any other details. A few cursory web searches found little.

Reply by Rich S yesterday
You can always count the teeth!
Don’t forget to include tire and wheel size in your calculation. The weight of the bike to a lesser extent since pushing a lighter bike with all else being equal would also be easier.

Reply by Cameron 7.5 mi yesterday
They’re standard Nexus 3-speeds. If you count the teeth on one you can plug the numbers into Sheldon Brown’s handy program to calculate what you need.

http://sheldonbrown.com/gears/internal.html

Reply by Andronymous yesterday
That’s why I brought this up, is there’s a chainguard and internal hub. I’m pretty sure no teeth are visible.
And even if they were countable in front, the hub may have gear trains and inner rings.
If no Divvy tech speaks up, I could eventually determine the ratios experimentally.

Reply by Skip Montanaro 12mi yesterday
Right, however, as Cameron indicated, the hub is a standard Nexus 3-speed. You should be able to count the cog and chainring teeth from the left side, then plug them into Sheldon’s calculator, select the Nexus 3-speed as the the hub, add in the tire and crank length info, then, voila! It will spit out three separate numbers in the units of your choosing.

Reply by Andronymous yesterday
Sure sure. I’d looked at the PDF of the hub, and found it a bit overwhelming. Only actually seems to contain two “sprocket wheels” (18+20).
And I can see wheel size and crank length effecting mileage and torque, but they’re not strictly relevant to a simple calculation of gear ratio are they? But if Sheldon want’s ’em, looks like I’m gonna hafta measure some things.
In advance of certainty, I’d venture Divvy speed #3 is about 3:1, and speed 1 is something like 9:1.

Reply by Rich S yesterday
Enter the same number of teeth into Sheldon’s calculator and then adjust the tire size and you’ll see the ratios change. I believe the rule is smaller diameter means lower gear/easier to pedal.
Same with crank length. Longer cranks require more force to pedal … or is it the other way around on cranks??? Either way it does impact the ratio.

Reply by Andronymous yesterday
A broader question y’all are touching I think is more like measuring power/distance.
I suppose yes, the usefulness of a simple cog/ring ratio for comparison breaks down when bikes are otherwise radically different. Still, being a nerd I hunger to know Divvy’s exact specs.
For the friend, I’m gonna put her on a 21 speed of near target size and ask her to pick her favorite gear, then count the teeth for that position, and just ignore the suggestion of Divvy’s 3rd gear as a sub-minimum reference.

Reply by Skip Montanaro 12mi yesterday
Sheldon Brown has a good treatise on measuring gears, and why you might want to consider crank length and wheel diameter, not just chainring and cog teeth:
http://sheldonbrown.com/gain.html
apples-to-apples-ly, y’rs…

Reply by Craig S. yesterday
Totally useless comment that needs no replies but I’m sure will garner them ensues:
Much as I am really enjoying my Divvy key, I thoroughly hate the gearing on these bikes. I’m a tall guy; the gearing is way too short or too long and the crank arms are too short. I HATE the gearing.
However, this is a great system for rides under 2 miles, anything longer and I want to throw the damn things in the river.

Reply by Hey! Bike Shop Guy yesterday
I find it a little weird that you are ‘specing’ a bike for somebody but not only seem unable to figure out a rough estimate on the gearing of a Divvy bike but apparently have little to no understanding how bicycle gearing works with wheel size and crank length to figure out gear inches.
Gear inches is a useful way to translate the overall gearing of a complete bike to a number that can be used to easily compare bikes of different wheel sizes and crank length. It basically gives you a number that represents the number of inches over the ground the bike travels for every pedal rotation; the farther it goes the higher the effort, and lower the cadence, will be to move at the same speed or accelerate at the same rate.
Count the teeth, front and rear, get the crank length and wheel size and enter it all into the Sheldon Brown gear inch calculator choosing the option for a Nexus 3spd and compare it to the numbers form your bikes set up. From there knowing the wheel/tire size of the bike you want to build you can pick a crank length and gearing for your friends bike that creates works out to a gear inch number in between the two.
Of course the more interesting question here is why, if you don’t know any of this are you trying to set up somebody’s bike? Have them go to a shop and get advice from a professional before you end up guiding them into a bad choice because you apparently don’t really know what the heck you are doing. DIY is great and all but pleas people know how to do it before you start.

Reply by ilter 17 hours ago
Another interesting question is whether you simply misspoke or if you are truly confusing gear inches and Sheldon Brown’s gain ratio 🙂

Reply by Hey! Bike Shop Guy 15 hours ago
The Sheldon Brown calculator will give you out put from all those numbers in gear inches, development or gain ratio as well as cadence at specific RPM. Gear inches is the number I like to use.

Reply by Juan 2-8 mi. 14 hours ago
At least for the Chicago market for these nation wide standard built machines, they should just change the rear cog to a smaller gear. Then maybe I will sign up for a Divvy membership.

Reply by Andronymous 12 hours ago
Agreed. I hope they’re aware, and through discussions like this reiteration is made, that their lowest gear is useless.
Putting aside the tangential value to supplement planning, the ridicule of the righteous gods of bikecraft, and the pursuit of more detailed metrics, the simple ratios sought here are non-obvious and worth knowing.
I’ll try to count and measure and weigh one this weekend. Followup with more research and contact them directly. Anyone wanna help?

Reply by AM 9.5 12 hours ago
I appreciate that the goal is that Divvy accomodates as many differently shaped people as possible for short trips. That said, I think they are geared too low for our mostly flat topography here. Third gear is adequate, but I think second, the middle, gear ought to be the target for the adequate gear.
It appears that Bixi-based bike share systems do have choices in how they equip and gear the bikes. I used one in SF late last year. The bike appears identical in all respects except that SF Bike Share bikes have a Nexus 7 speed hub (https://bayareabikeshare.com/meet-the-bike). The lowest gear was really, really low, perhaps lower than a Divvy, but it made sense given the hills. I did not have a chance to wring out the high gear because my one trip on SF Bike Share was nearly all uphill.
Not being an IGH expert, apart from cogs, are there options in gear ratios in the Nexus hub? Sturmey Archer has offered lower options for its standard 3-speed hubs (for instance, you can order a lower geared SA-equipped Brompton for hilly environs). Anyone used Citibike or Capitol Bikeshare?

Reply by Cameron 7.5 mi 8 hours ago
I believe that there is only one set of ratios for Nexus hubs. Changing the cogs will move the whole set up or down, but the steps between gears will remain the same.

Reply by Kevin C 8 hours ago
I think he’s looking for “gear inches,” but whatever. For those of you keeping score at home, I did send an email to Divvy customer service on 4/24 @ 1:52 pm asking this question. I have not received a response. I’ll post if and when I ever do.

Reply by Andronymous 7 hours ago
THANX KEVIN! I’d originally just wanted to know teeth on front / teeth on rear to start; all that’s ever mattered on my fixie. But now I wanna know all the specs, even it’s aerodynamic efficiency quotient. Anyone got a wind tunnel?
And good to hear about the other cities’ hubs.

Reply by ilter 6 hours ago
Yes, but is that supposed to address my comment? Did you even read my comment, pause for 10 seconds and think maybe you did misspeak? Or are you too confident for that possibility to cross your mind? You act like you know all about gear ratios, tell people to get advice from a pro, a pro like you I suppose, do all that in a condescending tone, yet what you write is inaccurate and very likely confusing for someone thinking or learning about these things for the first time. And after I take you seriously and read your long post, and hint that maybe you said something wrong.. what do you do? dump more wisdom, or should i say bullshit? And now what, perhaps you know a lot, you got lots to share, but why would I ever listen to what you have to say? Why would anybody?
So frustrating, and disappointing..

At Least No Newbies Were Harmed

So much for the ritual quotation of Corinthians 13. We are yet again returning to the kind of loving atmosphere that has made the ChainLink the envy of the Urban Cycling Community. It seems that even the exchange of technical information is an occasion for turning a perfectly good discussion into something embarrassing?

Anybody know why this sort of thing has to happen on a fairly regular basis? It is pointless and yet inevitable given the egos involved. I keep waiting for the ChainLink Community to grow a pair and politely usher out this trend in verbal engagement, but I fear that will never happen.

Time to go back and watch an episode of Reality Television. If you are going to watch people take themselves too seriously it might as well also be amusing. Sadly, this stuff is just depressing.

So Does This Really Represent The Best We Can Do?

ChainLink keeps winning awards as:

The Chainlink is the one-stop Chicagoland resource for connecting cyclists to share info on bikes, routes, rides, and events.

Why? There is precious little real information that gets “shared” with anyone that is not filtered through a self-appointed committee of “OnLine Harassers” two of whom are the stars of this episode of Reality Urban Cycling. Some of their supporting cast is off no doubt preparing to take their place should another newbie show up and ask whether helmets are OK to use. Is this really the best that the Chicago region can produce in the way of assistance to newbies? Is it even useful to cyclists who have been around for a while and merely want to “chew the fat” over “all things cycling“?