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.
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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.
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.
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.
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.
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.
Andronymous said:
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.
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.
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...
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.
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.
Another interesting question is whether you simply misspoke or if you are truly confusing gear inches and Sheldon Brown's gain ratio :)
Hey! Bike Shop Guy said:
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.
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.
ilter said:
Another interesting question is whether you simply misspoke or if you are truly confusing gear inches and Sheldon Brown's gain ratio :)
Hey! Bike Shop Guy said: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.
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.
Craig S. said:
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.
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