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Sprocket size on a 3 speed

Discussion in 'Folding Bikes' started by winjim, 17 Dec 2016.

  1. winjim

    winjim A youth of interminable age

    I have a 16" wheeled bike with a 52 tooth chainring and a 3 speed SA hub. The sprocket needs replacing so I just wondered what size those of you with a similar setup were using, and how you found the gearing. I need it low enough to get up the Sheffield hills...
     
  2. 12boy

    12boy Active Member

    Location:
    Casper WY USA
    I assume you have the 177% hub and not the wide range one designed for the two cog hub. I have a 14 which gives me 44.8 gear inches for a low, 59.7 for the middle and 79.6 for the top. For my needs I would really prefer a 13 ( the smallest available) which gives 48.2, 64.3 and 85.7. However, if you go to a 2 chain ring setup and add a 38 tooth chain ring you wind up with 37.2 , 43.6 and 58.1, at least with the 14 tooth cog. If you have a Brompton the chain tensioner will handle this easy peasy. You can shift with your greasy finger between the two chain rings which I do at a stop. I don't know the Sheffield hills but I can climb some fairly stout ones here with the 38 cog. When I get to the top I shift back to the big one for the ride home down hill. That trip takes about 3.5 miles to climb about a thousand feet.
     
  3. winjim

    winjim A youth of interminable age

    It's an AW so yes, I think it's 177%. None of your fancy chain tensioners or double chainrings though. :-) I guess the thing to do is to sit down and work out the gear inches and compare it to my road bikes.

    For reference, the steepest hill in the 2014 Tour de France, was in Sheffield.
     
  4. 12boy

    12boy Active Member

    Location:
    Casper WY USA
    www.sheldonbrown.com/gear-calc.html is the place I go to calculate gear inches. Quick and easy and you can print out the results and tape to your handlebars if you wish.
     
  5. mjr

    mjr Wanting to Keep My EU Citizenship

    www.gear-calculator.com has surpassed the Sheldon one for me.

    I usually run AW hubs as roughly 45/60/80 but gradients rarely get above 10% for long here. I'd probably sacrifice the top end in Sheffield (yes, I've tried cycling there), run 34/45/60 and still accept I'm honking or walking up some of the steepest. On 16" with 52-tooth chainring, I think that would mean 20 tooth sprocket.
     
  6. winjim

    winjim A youth of interminable age

    That's a good site. I like the sliders and the ability to do comparisons.

    I've just checked and the chainring is actually a monster 57 tooth. So for 34/45/60 you're looking at a 21 tooth sprocket. I'll probably go for a 22 which gives 32/43/58. That compares with my CdF which goes down to 32" on a triple chainset. Should be enough to get me up the hill to work.
    "Sorry if I look a bit knackered, I've been honking the Bickerton."



    I actually have two of these bikes, one is pretty knackered so I'm cannibalising it for parts. I think that one does have a 52 tooth chainring so I could always swap them over and go even lower. Once I've got this one roadworthy I might even build the other one up with some new parts. Could maybe go for the greasy fingered double as suggested by @12boy to give it a bit of top end.