smallest rear sprocket?

[twister]

What's the smallest rear sprocket I can put on a 3 speed nexxus hub? Also, where can I buy it? Thanks for your help, Dave.

 

[Bicycle808]

13t.
http://www.niagaracycle.com/categories/sturmey-archer-1-8-13t-coaster-brake-cog

Careful; that's gonna be a really high gear in 3.... Unless you're running a tiny front sprocket, too. =D

 

[Bicycle808]

Edit: oops.... i think you might need a dished rear sprocket for the Nexus 3, in which case you're stuck with a 16t.... sorry for any confusion.

 

[twister]

What I'm wanting to do is put a 25 tooth sprocket on my klunker.

 

[Bicycle808]

Oh. Here's some stuff to think about:
-According to Sheldon Brown, Nexus hubs require a dished cog. The smallest dished 3-tab cogs are 16t. Apparently, a flat cog will rub the hub body or something. I've never tried it myself; I'm a confirmed Sturmey-Archer guy.
-According to Shimano, the lowest direct-drive ratio that is safe to run with Nexus is 2:1, which would be 32x16, 34x17, or 36x18, et cetera...
-Ppl have successfully run lower ratios than that on Nexus.... Others have tried it, and turned their hub's insides into guacamole.
-If you run a 25x16, you might blow your hub up, and your top gear will only be 55". (You'll have a 30" low and a 40" middle gear.) Then again, you might love it.

 

[twister]

Once again, bicycle808, thanks for the help. I'll have to rethink this sprocket change.

 

[Bicycle808]

You're very welcome. If I were doing this, I'd "push my luck" by a tooth or 2, run something like a 30x16 or a 32x17 or something like that. It'd give you plenty of low, a little high, and I'm thinking it probably won't fry the innards. Shimano is probably a bit conservative on the minimum ratio front....