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Old 04-24-11, 07:49 AM   #1
mattdd60
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Trek 520 Crankset - Reducing Gear Inches

I will be self-supported touring down the Oregon Coast this summer. I would like to reduce my gear inches to 21, and am looking for advice on the most economical way to reach this low end gearing. Will a 26t chainring work OK with the derailer and chain? Or is this too much of jump to the 39t middle ring?

700/32 Tires
Crank Shimano Tiagra 50/39/30
Cassette SRAM PG970 11-32, 9 speed
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Old 04-24-11, 09:36 AM   #2
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I've got a 520 and run 48-38-24T chainrings and about the same cassette. I don't have any real problems as long as I don't try to jam the derailer/chain onto the middle from small rings while peddling hard. There's a little extra chain slack and bouncing when I'm climbing in "granny gear". Just don't run on the small ring with anything smaller than the 2nd/3rd gear in the rear.
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Old 04-24-11, 09:56 AM   #3
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What did you do with the crank it came with?

A 34T cassette wouldn't be expensive.

I have been meaning to ask about using a 36T cassette with a 9sp rear der.
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Old 04-24-11, 10:01 AM   #4
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Originally Posted by mattdd60 View Post
I will be self-supported touring down the Oregon Coast this summer. I would like to reduce my gear inches to 21, and am looking for advice on the most economical way to reach this low end gearing. Will a 26t chainring work OK with the derailer and chain? Or is this too much of jump to the 39t middle ring? 700/32 Tires Crank Shimano Tiagra 50/39/30 Cassette SRAM PG970 11-32, 9 speed
I ride with a 50-39-24 and a 11-34 cassette. Did not have to change anything.
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Old 04-24-11, 10:01 AM   #5
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I have a 12-36 cassette (shimano hg-61 I think) with a 9 speed deore derailleur and it works fine so far, but I haven't many km on this setup yet. It's paried to a 50/34 up front. It cost 60 bucks though, so if you can get a smaller granny ring to work with your existing setup I reckon that would be more economical.
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Old 04-24-11, 10:11 AM   #6
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Originally Posted by mattdd60 View Post
I will be self-supported touring down the Oregon Coast this summer. I would like to reduce my gear inches to 21, and am looking for advice on the most economical way to reach this low end gearing. Will a 26t chainring work OK with the derailer and chain? Or is this too much of jump to the 39t middle ring?

700/32 Tires
Crank Shimano Tiagra 50/39/30
Cassette SRAM PG970 11-32, 9 speed
We need to know what rear derailleur you are using, it is possible that you are beyond the chain wrap capacity of the RD after installing the 26t.

Besides that issue, the 26t will work fine, just install and Dog Fang to keep the chain where it belongs:
http://www.universalcycles.com/shopp...ls.php?id=6714


Last edited by Barrettscv; 04-24-11 at 10:24 AM.
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Old 04-24-11, 12:21 PM   #7
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I have used a 10 and 16 tooth difference and it worked well 50/40/24.
Just need to use Bar end shifters, they work well, Brifters are not so adaptable.

Read the Terrain .. The big Up-shift from the granny to the middle
is done at the crest of the hill, where you naturally let up on the pedal pressure ,
and start to coast down the other side, so taking the tension off the chain ,
and letting it shift.

Lots of well spec't touring bikes use a Mountain bike crankset,
now that 12 t cassettes are common the 50t chainring is overkill ..

a 95" gear is plenty high with a 700c wheel that was a 50/14 ..

but you may like the 22 t granny gear on a 44/32/22t chainset.
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Old 04-25-11, 07:05 AM   #8
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You will need a friction front shifter, but I assume you are using the stock friction bar end shifter so that should not be a problem for you. I think you should consider a 24t instead of a 26t if you want climbing ability.

I have a 52/42/24 front (Campy) and an eight speed 11-32 (11/12/14/16/18/21/26/32 SRAM) rear. I replaced the 30t smallest chainring with a generic aftermarket 24t. I have enough chain so that if I shift onto the largest front chainring (52t) and rear sprocket (32t), that I don't jam anything up. Unfortunately that is a couple more links than most chains are sold with on my LHT. With this gearing there is too much chain if I use the 24t front and the smallest (11t or 12t) sprockets on the rear, the rear cage won't wrap up all of the chain. But, I avoid using the two most cross chained gears with each chainring, so that means that I actually only use 18 of my 24 gears. Thus, this works great for me.

I can't comment on your front and rear derailleurs, I have a M739 XT rear and a vintage Suntour front, both work well for me. Shifting from the 24t up to the 42t chainring is not a smooth shift but I can usually make that shift in a distance of 25 to 50 feet. I set up my LHT with this gearing when I built it in 2004 and I liked this gearing so much that when I built up another touring bike a year ago, I set that bike up with identical components.

You should consider a chain catcher to make sure that the chain lands on the 24t (or 26t) on the downshift. I have not had any problems before I installed a catcher but a friend often had his chain fall onto the bottom bracket shell when he downshifted. I installed one as an insurance policy.

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Old 04-25-11, 09:11 PM   #9
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Originally Posted by late View Post
What did you do with the crank it came with?

A 34T cassette wouldn't be expensive.

I have been meaning to ask about using a 36T cassette with a 9sp rear der.
My 520 is a 2008 model and originally was built with the 50/39/30 crankset.
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Old 04-25-11, 09:26 PM   #10
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Originally Posted by Barrettscv View Post
We need to know what rear derailleur you are using, it is possible that you are beyond the chain wrap capacity of the RD after installing the 26t.

Besides that issue, the 26t will work fine, just install and Dog Fang to keep the chain where it belongs:
http://www.universalcycles.com/shopp...ls.php?id=6714


The rear derailleur is a Shimano Deore LX.

Last edited by mattdd60; 04-25-11 at 09:28 PM. Reason: changed to "Reply with Quote"
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