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Small Chainring?

Old 09-04-09, 07:43 PM
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zuwapa
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Small Chainring?

I recently purchased a used bike. I only have a large (44T) and medium (32T) chainring for the front. Since I use this bike for hauling (Surly - Big Dummy), I need to know how to go about locating the appropriate small chainring. Would I be looking for any 24T chainring?

Thanks in advance!
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Old 09-04-09, 07:44 PM
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What's the BCD of your crank? That gives you a minimum chainring size.
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Old 09-04-09, 08:09 PM
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Originally Posted by zuwapa View Post
I recently purchased a used bike. I only have a large (44T) and medium (32T) chainring for the front. Since I use this bike for hauling (Surly - Big Dummy), I need to know how to go about locating the appropriate small chainring. Would I be looking for any 24T chainring?

Thanks in advance!
Just looked at a Surley site, and it shows a triple that they call a "Surley Twirley" on front with a 26T small sprocket. Bet you could get another one from a dealer for sure. And perhaps they make a 24 for it. The chainring bolt diameter means everything in determining how small you can go.

I run a Sugino 24-34-44...



Greg
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Old 09-04-09, 08:16 PM
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Once you determine the BCD, just find a chainring that has that BCD and you'll be set. Inner chainrings aren't ramped or pinned so one from any manufacturer will do the trick.

Something from here will fit: http://www.universalcycles.com/shopp...p?category=674
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Old 09-04-09, 09:31 PM
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Originally Posted by zuwapa View Post
I recently purchased a used bike. I only have a large (44T) and medium (32T) chainring for the front. Since I use this bike for hauling (Surly - Big Dummy), I need to know how to go about locating the appropriate small chainring. Would I be looking for any 24T chainring?

Thanks in advance!
If the "middle" chainring is a 32, then you probably have a 94/58mm BCD spider on the bike. I'm going by these specs: http://www.surlybikes.com/new/crank_pop.html . A 58mm BCD spider will accept a chainring down to 20 teeth: http://www.vueltausa.com/products/ch...chainrings.htm . A 20 tooth chainring and 34 tooth rear cog ought to give you a gear low enough to tow a Chevy out of a ditch.
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Old 09-05-09, 06:02 AM
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My bike isn't the build from Surly's website.

I found that the large and medium Center-Center measurement is 74mm on a 4 bolt crank. The small C-C measurement is 47mm. How would my BCD be figured?

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Old 09-05-09, 07:29 AM
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Originally Posted by zuwapa View Post
My bike isn't the build from Surly's website.

I found that the large and medium Center-Center measurement is 74mm on a 4 bolt crank. The small C-C measurement is 47mm. How would my BCD be figured?
With a 4 bolt pattern, the center of bolt to the opposite center of bolt (not adjacent bolt) is your BCD.
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Old 09-05-09, 07:47 AM
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Ok - I had used this website for measuring information: http://sheldonbrown.com/gloss_bo-z.html#bcd

The opposite bolt distances are 105mm for the two outer chainrings. The small chainring has a distance of 65mm.
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Old 09-05-09, 08:08 AM
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Originally Posted by zuwapa View Post
Ok - I had used this website for measuring information: http://sheldonbrown.com/gloss_bo-z.html#bcd

The opposite bolt distances are 105mm for the two outer chainrings. The small chainring has a distance of 65mm.
Sounds like a 64/104 crankset. Here are some 22 and 24 tooth inner rings:

http://www.universalcycles.com/shopp...8&category=674
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Old 09-05-09, 03:44 PM
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Thanks, Joe. Is there any reason why I might choose one over the other (22T vs. 24T)?
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Old 09-05-09, 04:12 PM
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I'm personally a fan of having more gearing than I think I'll need because I never know when I might need it. On a bike used for hauling stuff, I would not hesitate to add the 22 tooth cog. It's only a 10 tooth drop from your middle ring and will give you a VERY low gear paired with any cassette. I've climbed hills offroad in the 22/32 combo so, while you may not encounter it daily, hills that need a gear like that are out there.
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