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Rear Derailleur Capacity

Old 06-24-13, 04:20 PM
  #1  
Ivanrf1
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Rear Derailleur Capacity

I checked on the disraeli gears website and it said the cog count was

•Maximum cog: 23 teeth
•Total capacity: 26 teeth

So can my derailleur handle 26 teeth? I hope so! Just bought the new cassette so i hope it works!
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Old 06-24-13, 04:43 PM
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Can i move or tune the derailleur to fit this?
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Old 06-24-13, 04:48 PM
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I'm always squeezing more cog under my RDs than are supposed to fit, sometimes with puzzling results.

Can i move or tune the derailleur to fit this?
The answer is "it depends." Lot of variables between RD capacity, chainwheel sizes, RD spring tension, and chain length (among others) will come into play. The only way to be really sure is put it all together and test it.

I bet if you let us in on what RD you're talking about, there are a few people here who could make an educated guess as to what it can really cover.
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Old 06-24-13, 04:53 PM
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Ivanrf1
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Originally Posted by Lascauxcaveman View Post
I'm always squeezing more cog under my RDs than are supposed to fit, sometimes with puzzling results.


The answer is "it depends." Lot of variables between RD capacity, chainwheel sizes, RD spring tension, and chain length (among others) will come into play. The only way to be really sure is put it all together and test it.
Oh ok well i guess we will have to wait and see
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Old 06-24-13, 05:07 PM
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26 teeth is not very many. I can't think of any derailleur that wouldn't be able to handle up to a 26t cog. I suspect you will be fine. That said...if you want help determining whether your rear derailleur can handle up that many cogs, you will get the best answers by telling us what type of derailleur you have.
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Old 06-24-13, 05:36 PM
  #6  
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Originally Posted by gaucho777 View Post
I can't think of any derailleur that wouldn't be able to handle up to a 26t cog.
As noted, there are many variables involved. My Huret Jubilee on a Tange TR dropout barely clears a 24T cog.
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Old 06-24-13, 05:44 PM
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Originally Posted by gaucho777 View Post
26 teeth is not very many. I can't think of any derailleur that wouldn't be able to handle up to a 26t cog. I suspect you will be fine. That said...if you want help determining whether your rear derailleur can handle up that many cogs, you will get the best answers by telling us what type of derailleur you have.
It is a suntour suprbe pro
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Old 06-24-13, 06:01 PM
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Originally Posted by Ivanrf1 View Post
It is a suntour suprbe pro
No problem.
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Old 06-24-13, 08:22 PM
  #9  
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Originally Posted by AZORCH View Post
No problem.
Sweet! Hope to see my new bike slowly come together!
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Old 06-24-13, 08:31 PM
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I have a Superbe Pro derailleur on the PX-10 pushing the chain across a 13-28t Shimano HG freewheel. There have been zero problems with the setup. You'll probably be just fine.
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Old 06-24-13, 09:12 PM
  #11  
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Above is from the 1985 Raleigh Catalog. The Prestige, Competition, Grand Prix all have about the same specs, different components to save a couple pounds. But, if it fits on one, it will fit on all.
With that said,

The OP had said he wanted these wheels to put on the Prestige..

http://www.ebay.com/itm/New-Wheelset...item4d0dcdc0d3

Somebody told him they were either too heavy or they wouldn't fit, since they are for the 8,9 and 10 speed.

I have the 85 Raleigh Prestige, Competition, and the Grand Prix

Here is the 85 Grand Prix which is just like his 85 Prestige, if they were side by side, I could swap every component of this Grand Prix and put it on his 85 Prestige, and everything would fit and the OPs bike would ride perfectly. BTW, this Grand Prix rides perfect..

It has the OEM SRX FD and a Sprint RD you can count the cogs to see how many speeds, I am sure there is a spacer in there, but can't say for sure.

Again, this bike is just like the OPs 85 Prestige..This bike was put together rather cheaply too, as the wheels were under $100 shipped..

The only component I didn't mention, was the skill of the builder of this bike, which is evident.









Every part on this bike, including those wheels will fit perfectly on the OPs 85 Prestige.

Last edited by cehowardGS; 06-24-13 at 09:20 PM.
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Old 06-25-13, 05:17 AM
  #12  
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That Max cog of 23 teeth listed on Disraeli Gears must an error, eh? Or maybe a Sun Tour recommendation?

Capacity is calculated as follows, as per Sheldon:

Dérailleurs usually are rated in terms of "tooth-difference capacity," a number that represents the dérailleur's capacity to take up slack in the chain. To find the minimum tooth-difference capacity needed for the gearing you have selected, subtract the number of teeth on your smallest rear sprocket from the number of teeth on the largest. Do the same for the front sprockets, and add the two numbers. For example, if your rear sprockets run from 14 to 26 teeth, the rear difference is 12. If your chainwheels are 36-52, the front difference is 16. Adding the figures for front and rear, we get a total difference of 28 teeth. If you get a dérailleur with a 28-tooth capacity or more, it should handle the range. If you use a dérailleur with insufficient tooth difference capacity, the chain will be too slack in some gears or too tight in others and you probably will not be able to get it to shift properly.
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Old 06-25-13, 05:53 AM
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The OP has yet to show a picture of the 85 Prestige that we have several threads on, not one picture?
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Old 06-25-13, 06:39 AM
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Originally Posted by rootboy View Post
That Max cog of 23 teeth listed on Disraeli Gears must an error, eh? Or maybe a Sun Tour recommendation?....
It could be an error but probably isn't. First off, it is spec'd for the matching Superbe dropout which has a short hanger length. Most frames have dropouts with longer hangers, which will gain an extra couple of teeth of large cog capacity. Cranking down on the B-tension screw will also gain an extra couple of teeth clearance but at the expense of chain wrap (around the cog, not derailleur chain wrap capacitiy) and subsequent shifting performance. Finally, by this period manufacturer's had gravitated from aggressive specifications to more conservative specifications, probably as result of their boom era experience with American consumer backlash.

The bottom line is that a 23T is probably a slightly conservative rating for optimum performance with a Superbe dropout. From that point of view you could view it as a recommendation. You may be able to get away with more, depending on circumstance, but possibly at the expense of shifting performance and, most importantly, at your own risk.
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Old 06-25-13, 06:56 AM
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Right T-Mar. Thanks. Not too familiar with Sun Tour myself but after all, the Superb was, essentially, a "racing" rear gear, and 23 would be on the high end of low cogs for that purpose, I would guess.
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Old 06-25-13, 12:08 PM
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Originally Posted by rootboy View Post
Right T-Mar. Thanks. Not too familiar with Sun Tour myself but after all, the Superb was, essentially, a "racing" rear gear, and 23 would be on the high end of low cogs for that purpose, I would guess.
The 23T max cog rating of the Suntour Superbe Pro was only for optimal index shifting; the friction max cog is 26t. This Suntour Accushift indexing system requires optimal percentage of chain wrap around the cog. A 23T cog has more percentage chain wrap than 26T.
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Old 06-25-13, 12:18 PM
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Originally Posted by onespeedbiker View Post
The 23T max cog rating of the Suntour Superbe Pro was only for optimal index shifting; the friction max cog is 26t. This Suntour Accushift indexing system requires optimal percentage of chain wrap around the cog. A 23T cog has more percentage chain wrap than 26T.
While it's true that a friction system can get by with less chain wrap, the pre-AccuShift version of Superbe Pro was rated at 23T with the short SunTour dropout.
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Old 06-25-13, 12:40 PM
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I still remember my ~1985 Allez with it's 6s Accushift Sprint gruppo, It didn't seem to like the 26t freewheel I installed.

I tweaked it here and there, and modernized the chain (was Sedisport), and was finally able to use the 26t freewheel.
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Old 06-25-13, 01:05 PM
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Sometimes you can squeeze another cog in by moving your rear axle farther back in the drop - Here a link to this discussion...

http://www.bikeforums.net/showthread...On-Older-Bikes
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