# "Max sprocket" and "total capacity"? What's the diff?



## Drone 5200 (Mar 3, 2003)

What's the difference between "maximum sprocket" and "total capacity" for a derailleur? 

Shimano's website says the RD-7700 and RD-7800 have a max sprocket of 27T and a total capacity of 29T. While the RD-7703 has a max sprocket of 27T and a total capacity of 38T. 

What is "total capacity"?


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## TurboTurtle (Feb 4, 2004)

Drone 5200 said:


> What's the difference between "maximum sprocket" and "total capacity" for a derailleur?
> 
> Shimano's website says the RD-7700 and RD-7800 have a max sprocket of 27T and a total capacity of 29T. While the RD-7703 has a max sprocket of 27T and a total capacity of 38T.
> 
> What is "total capacity"?


Max sprocket has to do with the parallelogram movement of the RD. It moves down as it moves in to miss a cog that has 27 teeth.

Total capacity is how much chain wrap it is capable of. The 29 tooth is a double ((53+27)-(39+11))= 30 (close enough I guess???) while the 38T is a triple ((52+27)-(30+11)= 38.

TF


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## Kerry Irons (Feb 25, 2002)

*Strange approach to math!*

While your equation gives the right answer, capacity is usually thought of as the difference between the chain rings plus the difference between the largest and smallest cogs. E.g. 53-39 + 23-13 = 24 total teeth. While the math of (53+23) - (39+13) gives the same answer, it seems a strange way to think about it.


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## torquecal (Nov 9, 2002)

Turbo and Kerry give spot on answers... I think of it a little differently, but it just helps me wrap what braincells I have left around the concept:

Maximum Sprocket = what shimano says is the biggest cog I can put back there. In reality there are times when I might be able to get away with a tooth or two more.

Total Capacity = how much chain the pulley cage is designed for... just how much can it take up the slack? The bigger values are the long cage types, usually mean't for triple chainrings, while the smaller values are for doubles.



Drone 5200 said:


> What's the difference between "maximum sprocket" and "total capacity" for a derailleur?
> 
> Shimano's website says the RD-7700 and RD-7800 have a max sprocket of 27T and a total capacity of 29T. While the RD-7703 has a max sprocket of 27T and a total capacity of 38T.
> 
> What is "total capacity"?


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## JimGR (Feb 23, 2003)

*Thanks for asking*



Drone 5200 said:


> What's the difference between "maximum sprocket" and "total capacity" for a derailleur?
> 
> Shimano's website says the RD-7700 and RD-7800 have a max sprocket of 27T and a total capacity of 29T. While the RD-7703 has a max sprocket of 27T and a total capacity of 38T.
> 
> What is "total capacity"?


I was needing to know the same thing.


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## Drone 5200 (Mar 3, 2003)

Drone 5200 said:


> What's the difference between "maximum sprocket" and "total capacity" for a derailleur?
> 
> Shimano's website says the RD-7700 and RD-7800 have a max sprocket of 27T and a total capacity of 29T. While the RD-7703 has a max sprocket of 27T and a total capacity of 38T.
> 
> What is "total capacity"?


WOW! I'm impressed. You are a knowledgeable crowd. Thanks for sharing the wisdom. And so fast, too. 

One follow-up: Is that 27T max for real? Anyone with experience using a 29T on the RD-7800?


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## torquecal (Nov 9, 2002)

I haven't done it myself, but I have seen it done. The one bike I saw it on worked fine.



Drone 5200 said:


> WOW! I'm impressed. You are a knowledgeable crowd. Thanks for sharing the wisdom. And so fast, too.
> 
> One follow-up: Is that 27T max for real? Anyone with experience using a 29T on the RD-7800?


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## Spoke Wrench (Aug 20, 2001)

Drone 5200 said:


> WOW! I'm impressed. You are a knowledgeable crowd. Thanks for sharing the wisdom. And so fast, too.
> 
> One follow-up: Is that 27T max for real? Anyone with experience using a 29T on the RD-7800?


Exceeding the 27t max gear limit usually requires screwing the b adjustment screw all the way to pull the derailleur beck behind the cogs so that it doesn't rub. I've heard of guys even replacing the stock screw with a longer one.


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## TurboTurtle (Feb 4, 2004)

*Usually we think the same...*



Kerry Irons said:


> While your equation gives the right answer, capacity is usually thought of as the difference between the chain rings plus the difference between the largest and smallest cogs. E.g. 53-39 + 23-13 = 24 total teeth. While the math of (53+23) - (39+13) gives the same answer, it seems a strange way to think about it.


but on this one I have to disagree. We're looking for the maximum difference in chain wrap. The "shortest" is on big-big (53+23) and the most the derailleur has to take up is on the small-small (39+13). The difference seems the most logical way to visualize the concept.

TF


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## contato.alexssandro (10 mo ago)

TurboTurtle said:


> *Usually we think the same...*
> 
> 
> 
> ...


Something makes sense. My problem: 1x system. I Can a 48 chainring with 10-42 cassette. My xt 8000 rear derailleur (11 speeds), total capacity 39T? With you, I would have (48+10) - (48-42) = 32. correct?


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## ogre (Dec 16, 2005)

Odds are that 25% of the responders to this thread have passed away since the last reply 18 years ago, so I’ll respond. You are correct.


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## velodog (Sep 26, 2007)

ogre said:


> Odds are that 25% of the responders to this thread have passed away since the last reply 18 years ago, so I’ll respond. You are correct.


What about the other 75%?


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## cxwrench (Nov 9, 2004)

What is up with all these new guys dredging massively old threads? Don't you guys have any experience at all w/ online forums? Check the date of the last reply.


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## contato.alexssandro (10 mo ago)

ogre said:


> Odds are that 25% of the responders to this thread have passed away since the last reply 18 years ago, so I’ll respond. You are correct.


TKS. RIP.


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## Lombard (May 8, 2014)

cxwrench said:


> What is up with all these new guys dredging massively old threads? Don't you guys have any experience at all w/ online forums? Check the date of the last reply.


Google searches bring people here. It's easy to not pay attention to the date and reply. Not that I would ever do a thing like that.


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## Finx (Oct 19, 2017)

cxwrench said:


> What is up with all these new guys dredging massively old threads? Don't you guys have any experience at all w/ online forums? Check the date of the last reply.


There is also the fact that when people ask questions that have been answered many times over many years, they are asked "WHY DON'T YOU USE SEARCH?".

There is no right answer. In some cases bringing up an old thread brings details that might be relevant to the conversation.


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## ogre (Dec 16, 2005)

contato.alexssandro said:


> TKS. RIP.


Who is that? I know of a couple that have passed, but not ones in this thread.


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## ogre (Dec 16, 2005)

velodog said:


> What about the other 75%?


74.999% of them went to FB.


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## Lombard (May 8, 2014)

ogre said:


> Who is that? I know of a couple that have passed, but not ones in this thread.


Who did you know here who passed? How did you find out?


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## ogre (Dec 16, 2005)

Lombard said:


> Who did you know here who passed? How did you find out?


Platy and Hollywood come to mind. Found out through here.


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## Lombard (May 8, 2014)

ogre said:


> Platy and Hollywood come to mind. Found out through here.


Hmmm. Those names don't ring a bell. I've only been here since 2014. There are others I knew here who used to post and suddenly disappeared. One has to wonder about people who suddenly stop posting.


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## ogre (Dec 16, 2005)

cxwrench said:


> What is up with all these new guys dredging massively old threads?


This is why. #1 result. The people that pay the bills want this. I attribute this to phenomena to coming to the surface when updated to the 'Facebook' format. Give the posters slack for not noticing the date.


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## cxwrench (Nov 9, 2004)

contato.alexssandro said:


> Something makes sense. My problem: 1x system. I Can a 48 chainring with 10-42 cassette. My xt 8000 rear derailleur (11 speeds), total capacity 39T? With you, I would have (48+10) - (48-42) = 32. correct?


42-10=32. That's it. You only have 1 chainring, no need to complicate it.


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## ogre (Dec 16, 2005)

cxwrench said:


> 42-10=32. That's it. You only have 1 chainring, no need to complicate it.


Actually you do need to slightly complicate it. Since he's running a 1x you need to divide by one. 😎


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## contato.alexssandro (10 mo ago)

Sorry. I was really misled by Google. And in all these years, I think this doubt is very current. Gravel, and so many things that didn't exist, like the current 1x13 groups. So I didn't realize the matter was buried and dead. But it revived quickly. Thanks.


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## Lombard (May 8, 2014)

contato.alexssandro said:


> Sorry. I was really misled by Google. And in all these years, I think this doubt is very current. Gravel, and so many things that didn't exist, like the current 1x13 groups. So I didn't realize the matter was buried and dead. But it revived quickly. Thanks.


Sometimes all a thread needs is some CPR. 🤣


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