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Old 07-17-09, 10:58 PM   #1
kamtsa
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Help me selecting a chainring for my bike

My touring bike has a DualDrive 3x9 with SRAM DualDrive, single 46T 110mm Suginu chainring, ERTO 406 Kojak wheels and SRAM pc951 chain. This results in a gear inch range of 19.6” to 106”.

I would to move down the range by changing the chainring from 46T to 40T. I found on Amazon several 40T 110mm chainrings but am not sure which will be the best fit my bike and what are the differences between them, quality wise:

http://amzn.com/B001GSQV9O
http://amzn.com/B001CJXDS4
http://amzn.com/B001GSOHF4
http://amzn.com/B000C15JYY

Any suggestion? Will any 40T 110mm chainring fit my bike? Does the quality of the chainring matter (I don’t have FD if it makes a difference) or are they all the same?

Also, how much should I shorten the chain when going from 46T to 40T?

Thanks,

Kam
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Old 07-17-09, 11:28 PM   #2
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Did I read that correctly? You're running a single chainring on a triple crank? Anyways, that surly *stainless* chainring would be the best out of the ones you listed. Although the rest of those (al rings) are fine as well. Do the proper chain sizing when you throw the 40t on. e.g big/big method. This gives you the correct chain length.
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Old 07-18-09, 12:46 AM   #3
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believe the op is refering to a rear hub that has an internal 3 speed and a 9 speed cassette, hence
no FD, agree with the stn stl gear and shorten chain as needed.
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Old 07-18-09, 01:05 AM   #4
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Oh you're right. Brain fart...
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Old 07-21-09, 05:17 AM   #5
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Thanks operator and roberth33tiger.

Kam
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Old 07-21-09, 05:34 AM   #6
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Surly would last the longest. Then the Profile, FSA and last Sugino
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Old 07-21-09, 05:39 AM   #7
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Be sure the SRAM hub doesn't have a minimum gear ratio specification, i.e. the smallest chainring/largest cog combination they recommend. If you gear it too low there is a possibliity that the excess torque could damage the internal gearing.

BTW, 19.5 gear-inches is REALLY low. Do you need a still lower gear?
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Old 07-21-09, 06:50 AM   #8
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Originally Posted by HillRider View Post
BTW, 19.5 gear-inches is REALLY low. Do you need a still lower gear?
Actually I need more strength ;-)

Seriously, some of the hills I climb are unsustainable for me. That is, I can climb them for limited distance and it is getting harder as I go.

Kam
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Old 07-21-09, 07:04 AM   #9
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Be sure the SRAM hub doesn't have a minimum gear ratio specification, i.e. the smallest chainring/largest cog combination they recommend. If you gear it too low there is a possibliity that the excess torque could damage the internal gearing.
Let's say for a given hill and my current lower gear I go at 3mph. If I reduce the chainring to 40T and go at speed <= 3mph, the torque on the IGH is not increased, right?

My goal is to keep the same cadence as now but to reduce the force on the pedals (that is, lower power and lower forward speed).

Does this make sense?

Kam
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