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Old 11-10-10, 05:14 PM   #1
pjcampbell
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Campy 13-28 with Miche 28 and short derailleur?

Will this work with no rubbing... If not, 13-27?

Thinking about a 13-14-15-16-17-19-21-23-26-27 or 28 From a stock Centaur 13-26 (removing 18?)

thanks.

Last edited by pjcampbell; 11-10-10 at 05:20 PM.
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Old 11-11-10, 01:45 AM   #2
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The 26 to 27 shift is less than a 4% increase, that hardly seems worth it. Above 25 teeth, 3 tooth jumps always work best for me.
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Old 11-11-10, 01:59 AM   #3
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The 26 to 27 shift is less than a 4% increase, that hardly seems worth it. Above 25 teeth, 3 tooth jumps always work best for me.
Agreed.

Hopefully someone can answer your question. You may be able to pull up info on the derailer that will give you MAX gear size. You didn't tell us what derailer.
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Old 11-11-10, 05:29 AM   #4
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Campy recommends a spread of 15 for the Max. I use a 13 -29 10 spd cassette with a 53/39 on the front without any problems. I have a 13 - 28 (a canadian company sold a 28 tooth for the old EXA cassette) on an older campy 8 speed short cage with no problem either.
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Old 11-11-10, 06:49 AM   #5
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You use a 13-29 with no problems on a short derailleur?

I am undecided about 27t or 28t. If 28t fits, I will go for it. I did a quick estimate and we are talking about 74RPM, 77RPM and 80RPM at around 12% for 26t, 27t and 28t at my race pace.

Sorry it's a 10 speed Record rear derailleur. It says:
Largest Cog26teethChain Wrap Capacity27teeth
Not sure what chain wrap capacity is vs largest cog.

I have a compact in the front 34/50, also Campy Record, and I would like to throw in a Miche 28t back there if it is not going to cause problems. Obviously may have to make adjustments and/or increase chain length but I am more talking about the cog hitting the pulleys versus minor adjustments.

Last edited by pjcampbell; 11-11-10 at 07:02 AM.
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Old 11-11-10, 09:18 AM   #6
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Largest Cog26teethChain Wrap Capacity27teeth
Not sure what chain wrap capacity is vs largest cog.
Here's some helpful info: largest cog compatibility is pretty straightforward, it's the largest cog the manufacturer feels confident you'll be able to use with the derailleur without the upper pulley bumping into the largest cog on the cassette. Keep in mind, it's not a hard and fast number. There can be a variation of several teeth based on where, exactly, your derailleur hanger puts your derailleur relative to the rear axle. Longer hangers will allow a larger cog, for example. It really does vary from frame to frame, so the only real way to know if a certain combo will work is to try it.

Chain wrap capacity is a completely different issue. Keep in mind, a rear derailleur has two main functions: move the chain from cog to cog, and keep the chain tensioned properly. The chain tension function works because of the spring action of the cage, which allows the derailleur to keep steady tension on the chain even as the chain moves from cog to cog or from chainring to chainring up front. In other words, it "wraps" the excess chain, and a derailleur can only wrap so much; this is known as it's chain wrap capacity. The longer a derailleur's cage, the more chain it can "wrap." A drivetrain has a maximum chainwrap requirement, and to insure that the chain will remain tensioned properly in all possible gear combos, you need a derailleur that has enough chain wrap capacity to meet the maximum chainwrap requirement of the drivetrain.

A simple formula is used to determine a drivetrain's max. chain wrap requirement: Largest chainring minus smallest chainring plus largest cog minus smallest cog equals max. chainwrap requirement. Example: 53-39+28-11=31. So a drivetrain with a 53/39 crankset combined with a 11 x 28 cassette would need a derailleur with a chainwrap capacity of 31 teeth. This assumes the chain is sized so that it is only as long as necessary to safely cover the big ring/largest cog combo.

ALWAYS size your chain at least long enough to cover the big/big combo; the results can be catastrophic if it will not and you shift to this combo. On the other end, smallest chainring/ smallest cog, a little slack in the chain is not nearly as big a concern; of course you shouldn't be in this combo anyway, so if you're going to use a deraiilleur with not quite enough chainwrap capacity for your drivetrain, make sure the chain's long enough to cover big/big and try to avoid small chainring/smallest cog or two.

Last edited by well biked; 11-11-10 at 09:21 AM.
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Old 11-11-10, 01:58 PM   #7
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Here's some helpful info: largest cog compatibility is pretty straightforward, it's the largest cog the manufacturer feels confident you'll be able to use with the derailleur without the upper pulley bumping into the largest cog on the cassette. Keep in mind, it's not a hard and fast number. There can be a variation of several teeth based on where, exactly, your derailleur hanger puts your derailleur relative to the rear axle. Longer hangers will allow a larger cog, for example. It really does vary from frame to frame, so the only real way to know if a certain combo will work is to try it.

Chain wrap capacity is a completely different issue. Keep in mind, a rear derailleur has two main functions: move the chain from cog to cog, and keep the chain tensioned properly. The chain tension function works because of the spring action of the cage, which allows the derailleur to keep steady tension on the chain even as the chain moves from cog to cog or from chainring to chainring up front. In other words, it "wraps" the excess chain, and a derailleur can only wrap so much; this is known as it's chain wrap capacity. The longer a derailleur's cage, the more chain it can "wrap." A drivetrain has a maximum chainwrap requirement, and to insure that the chain will remain tensioned properly in all possible gear combos, you need a derailleur that has enough chain wrap capacity to meet the maximum chainwrap requirement of the drivetrain.

A simple formula is used to determine a drivetrain's max. chain wrap requirement: Largest chainring minus smallest chainring plus largest cog minus smallest cog equals max. chainwrap requirement. Example: 53-39+28-11=31. So a drivetrain with a 53/39 crankset combined with a 11 x 28 cassette would need a derailleur with a chainwrap capacity of 31 teeth. This assumes the chain is sized so that it is only as long as necessary to safely cover the big ring/largest cog combo.

ALWAYS size your chain at least long enough to cover the big/big combo; the results can be catastrophic if it will not and you shift to this combo. On the other end, smallest chainring/ smallest cog, a little slack in the chain is not nearly as big a concern; of course you shouldn't be in this combo anyway, so if you're going to use a deraiilleur with not quite enough chainwrap capacity for your drivetrain, make sure the chain's long enough to cover big/big and try to avoid small chainring/smallest cog or two.
Someone who knows what he's talking about. Wow.
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Old 11-11-10, 02:11 PM   #8
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Campy under rates the short cage RD's actual wrap capacity. The 27T value is just the maximum difference between the cogs and chainrings, sold at that time. The same RD that was once said to have only a 27T wrap was able to wrap a 50/34 with a 12-25 (29T) after compact cranks came out.

Some people get by using a short cage with a 53/39 and 13-29, but it does not have the wrap capacity for a 50/34 with a 13-28 or 13-29 on all bikes. You really need a medium cage RD.

One thing that is rarely considered is that chainstay length affects the wrap capacity. The perfect chainstay length can add up to 3T of wrap compared to the worst case. Go to the Park tool website and plug the proper numbers in the rigorous chain length formula to find what chain length is required for your setup. If you get a length like 53.25 inches, you have to use 54 inches and that's a worst case. If the number is just under a whole inch value, like 53 or 54 inches, then you have a best case, using every bit of chain available.

FWIW, the current 11 speed short cage RD can handle a 50/34 with a 12-29, but that required a different B screw mechanism to swing the upper pulley further back to clear the 29T cog. Only 2010 and newer RDs have that.
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Old 11-11-10, 04:29 PM   #9
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FWIW, the current 11 speed short cage RD can handle a 50/34 with a 12-29, but that required a different B screw mechanism to swing the upper pulley further back to clear the 29T cog. Only 2010 and newer RDs have that.
It's the same B screw mechanism, it's just the spring is changed to a different position.
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Old 11-11-10, 04:59 PM   #10
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It's the same B screw mechanism, it's just the spring is changed to a different position.
Wrong. It's part number 5-RD-SR004 that needs replaced. The spring does not limit the travel, you need more teeth to engage the B screw. See page 26 of the PDF.

http://www.campagnolo.com/repository...0-A-010909.pdf

Last edited by DaveSSS; 11-11-10 at 05:20 PM.
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Old 11-12-10, 04:58 AM   #11
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my chain stay length came up with like 53.89 or something

50-34+28-13 = 31.

I guess I can try the 28t and see what happens.

Last edited by pjcampbell; 11-12-10 at 05:10 AM.
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