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Help with Shimano Tiagra Rear Derailleur capacity

Old 03-21-12, 08:33 AM
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VT_Speed_TR
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Help with Shimano Tiagra Rear Derailleur capacity

I have a 2011 Salsa Casseroll with a Shimano Tiagra-GS cage rear derailleur. As delivered, it has a triple up front (26,36,48) with a rear cluster of 12-25. Great fun ride for day rides, I love the closely spaced gearing. However, thinking I may use this bike for a CC tour, and I'd like to have some lower gearing. Shimano's documents on the rear Tiagra indicates a 22 tooth range for the front and a max of a 27 tooth on the rear.

I'm wondering if anyone has pushed the rear to a 11-30 cluster? If I don't cross shift the gearing will the rear derailleur handle it? Or should I look to change the front to a 24,36-46 set? Still not as low as I'd want though unless I get a rear derailleur that has the max 27.

Thanx's
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Old 03-21-12, 09:24 AM
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I have a long cage(SGS?) on my touring bike with 20-34-46------14-34.It won't cross chain the small small without slack in the chain,but who does that anyways.

My old Shimano 600,which by todays standards would be a med cage(GS?),would handle it,I just wore it out.

Last edited by Booger1; 03-21-12 at 09:36 AM.
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Old 03-21-12, 09:30 AM
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SGS is the longer cage, GS a bit shorter, FYI.
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Old 03-21-12, 10:31 AM
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Originally Posted by fietsbob View Post
SGS is the longer cage, GS a bit shorter, FYI.
The GS cage is a mid cage I believe and is more road oriented. I may just have to order a cassette and give it a try. The Casseroll drivetain seems to be a mix, what with the low triple up front. It also uses brifters, so I think that may limit the derailleur choices. Harris Bicycle in Boston has a custom 13-30 cassette, expensive but I may give it a try since it appears to be design with what I want. close spacing in the high gears and some low gears at the other end. All of which are nicely spaced.

Last edited by VT_Speed_TR; 03-21-12 at 10:53 AM.
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Old 03-21-12, 01:27 PM
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For the price of one those Harris Cyclery cassettes, you can buy a 13-32 off-the-shelf cassette and a mountain RD (with an SGS cage) and be assured that you can reach the 32t sprocket as well as pull enough chain slack. The Tiagra RD only pulls 37t while a mountain RD pulls 45t. Your brifters will still work.
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Old 03-21-12, 10:04 PM
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pexio
For the price of one those Harris Cyclery cassettes, you can buy a 13-32 off-the-shelf cassette and a mountain RD (with an SGS cage) and be assured that you can reach the 32t sprocket as well as pull enough chain slack. The Tiagra RD only pulls 37t while a mountain RD pulls 45t. Your brifters will still work
+1

However, why not go for an 11-34, and give yourself a broader range of gears?

I tried one of Harris's 13-30 with a Shimano 105 LC rear derailleur, and I could not make it work to my satisfaction. I replaced the 30 tooth cog with a 11 tooth cog, and put it on my road bike. It gave me an 12-27. It is an Ultergra cassette, and that was a good use for it.

After talking to the folks at Harris, they sent me the 12 tooth cog at no extra cost.

The way they build the 13-30 cassette is to add a spacer and 30 tooth cog, and remove the 12 tooth cog from the stack of a stock 12-27 Ultegra cassette. the first 3 or 4 cogs are loose, while the rest are affixed to a carrier. The 30 tooth cog is just loose and is separated from the carrier by a spacer as you install the cogs. It is a cog from a low end cassette that was bolted or riveted together rather than using a carrier.


Last edited by Doug64; 03-22-12 at 11:25 AM. Reason: Correct the number of teeth
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Old 03-21-12, 11:30 PM
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I have a Tiagra RD on my Surly Crosscheck (not sure which variation of Tiagra, it's the stock for 2005). I added a 22 tooth front chain ring and changed the cassette out to 11-32. I've put thousands of miles on it since then with no problems.
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Old 03-22-12, 06:24 AM
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Originally Posted by hopperja View Post
I have a Tiagra RD on my Surly Crosscheck (not sure which variation of Tiagra, it's the stock for 2005). I added a 22 tooth front chain ring and changed the cassette out to 11-32. I've put thousands of miles on it since then with no problems.
May just need to "flip" the logic and do what you indicated. Much easier to just swap to a smaller chainring in front. I think I have a 24 in the parts bin, but a 22 would be even better.
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Old 03-22-12, 06:53 AM
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Originally Posted by VT_Speed_TR View Post
I have a 2011 Salsa Casseroll with a Shimano Tiagra-GS cage rear derailleur.

I'm wondering if anyone has pushed the rear to a 11-30 cluster? If I don't cross shift the gearing will the rear derailleur handle it? Or should I look to change the front to a 24,36-46 set? Still not as low as I'd want though unless I get a rear derailleur that has the max 27.

Thanx's
I used a Sram 11-32 cassette with a Shimano "GS" (long arm-road) rear derailleur last year and had no issues with a 32 size cog. Fitting a 12-30 should not be a problem.

Also, the Shimano "GS" (long arm-road) rear derailleur also has huge chain wrap and cog size capacity that is much greater than stated on the Specifications.

The chain-wrap limit of the Tiagra/105/Ultegra GS, according to Shimano, is 37. I'm operating safely, with every gear combination, using a chain-wrap value of 42. It is also possible to exceed the 27t Cog size capacity and use a 32t. I've combined a 50, 39 & 26 Crankset with the 10 speed Tiagra 12-30 cassette.

The practical chain-wrap capacity, with a correct length chain, of the road "GS" RD allows the big-big combination of 50t front Chainring & 30t rear cog with a little safety margin and also allows the small-small combination of 26t & 12t without any slack in the chain.



I'm also using a Shimano "GS" (long arm-road) rear derailleur with a 48, 36 & 22t triple with a 12-27 cassette with no problems. I'm sure a the 12-30 Century special from Harris would also work on this drivetrain.

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Last edited by Barrettscv; 03-22-12 at 09:22 AM.
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Old 03-22-12, 11:10 AM
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Originally Posted by Barrettscv View Post
I used a Sram 11-32 cassette with a Shimano "GS" (long arm-road) rear derailleur last year and had no issues with a 32 size cog. Fitting a 12-30 should not be a problem.

The Shimano "GS" (long arm-road) rear derailleur also has huge chain wrap and cog size capacity that is much greater than stated on the Specifications.

I've combined a 50, 39 & 26 Crankset with the 10 speed Tiagra 12-30 cassette.

The chain-wrap limit of the Tiagra/105/Ultegra GS, according to Shimano, is 37. I'm operating safely, with every gear combination, using a chain-wrap value of 42. It is also possible to exceed the 27t Cog size capacity and use a 32t.

The practical chain-wrap capacity, with a correct length chain, of the road "GS" RD allows the big-big combination of 50t front Chainring & 30t rear cog with a little safety margin and also allows the small-small combination of 26t & 12t without any slack in the chain.
This is great to hear. I think I may just spend the $25/$30 for an 11-30 cassette that I found on sale and give it a try. But from your experience it sounds like my original thoughts were correct, the Shimano listed limits in their tech doc's are on the conservative side. I also have a 24 chainring on another bike with a Jump-Stop that I could switch over to get the gearing even lower. I love the close gearing on the Casseroll, but if I'm going to load 10-15 lbs on it and do a CC tour, I just want a little safety margin for spinning up hills.
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