Pete, I have tried it. I was told a 9spd der. would work. It didn't. It isn't that the range isn't wide enough, it is that the space between clicks is off. If you hold a 9 spd and 10 spd der. side by side, the linkages are different lengths. What that translated to for me was that I could make it shift properly at either the top end of the cassette, or the bottom end. But not all the way through the range. The throw of the der. was just off enough in comparison to the shifter, that by the time it went 6 or 7 clicks, it wouldn't hit the gears. New 10 spd der. Problem solved.

Landshark,

Thanks for the reply. That is the kind of explanation that I expected from my LBS. But what I got was "the difference between the 7700 series and 7800 series derailleurs is that one is 9spd and one is 10spd." I gotta say that is a brilliant response. Anyway thanks again, I can now understand why the need for a 7800 series derailleur.

Pete

I haven't tried it.

But are you desiring to use the 7700 rear der. with 7700 or 7800 shifters? Because I would bet good money that it (7700 der. on 10 spd cassette) would work, IF you use 10-speed (7800) shifters (that is the critical part) with the 9-spd. derailleur.

Have you tried that?

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Where would you want to swim ?

That was my set up. 10 spd shifters, cassette and chain. 9 spd der. I was convinced the problem was my mechanical abilities until I crashed and scuffed the der and wife bought a new one for b-day. Problem soved.

Interesting...

If the 10 spd deraill. (7800) is supposed to work on a 9 spd cassette (with 7700 shifters) according to shimano, why wouldn't the 9 spd deraill. (7700) then work on a 10 spd cassette (with 7800 shifters)?

a puzzle...

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Where would you want to swim ?

That is what I was assuming as well, because all of the indexing is housed in the shifters not the derailleurs. Anyway what Landshark said does makes sense. If there is enough difference in the length of movement for each indexed click is just slightly larger with 7700 series derailleur than with a 7800 series derailleur that would result in throwing off the shifting at one end or the other. Atleast I am following his logic.

Yes, and he tested it too.

But then it seems that the 10-spd deraill shouldn't work on the 9-spd deraill (which shimano says will work w/ 9 spd shifters)--that is the puzzle.

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Where would you want to swim ?

I forgot about that. Hmmm, that makes this even more of a puzzle. Guess, I will have to give this a go and see what happens. Worst case scenario I end up buying a new rear derailleur.

And let us know what happens with your test.

And if you want the "shimano opinion", try calling 949-951-5003 x 2, x 1 for bike tech support.

Good luck...

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Greg,

I will let you know how it goes. I absolutely will call Shimano, but I expect that they will say you cannot mix 7800 shifters with 7700 derailleurs but you can mix 7800 derailleurs with 7700 shifters. I am perplexed as to why but again I will let you know how it turns out.

Pete

First, 10spd cassette is narrower than a 9spd cassette since you have to use a spacer for the 10spd cassette on a 7700 series compatible cassette body.
WRONG, you have to use the spacer however there is material removed from the back of the cassette's alloy cog carrier so that the last position cog actually moves further over the end of the freehub body. Center to center dimension from the 1st cog to the 10th cog is wider than the center to center dimension on 9speed.

Second, if the first assumption is true than the 7700 series rear derailleur should have enough travel to accomodate a 7800 series cassette.
CORRECT. It does move enough. It'll move enough to cover 12 speeds. The limits screws will accomodate a wide varitey of frame specs.

Third, I will use a 10spd chain. If all of this is true why do I have to use a 7800 series derailleur instead of a 7700 series derailleur?
Because of the cage and pulley design. The 10 speed derailleur has less float in the upper jockey wheel. The additional float in the 9 speed derailleur give poor performance in the extremes because the "float" allows contact between adjacent cogs. In the extremes, the chainline pulls the floating top pulley over enough to hit the cog closest to it.


I consider myself to be a decent home wrench and cannot figure this one out. Has anyone experimented with the set-up I have described and if so what were your results?

I'm an ok mechanic too, you can replace the floating pulleys and it'll work ok, but then why upgrade to 10 speed if you want "ok" performance?

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

SuperDave,

Thank you very much! I wish all LBS mechanics had this kind of knowledge, it would solve all sorts of problems and instill much more confidence in them.

So much for my experiment, but good to know that I can save myself some effort, frustration, and pain.

Thanks again, Pete

Mechanics at Bike Shops (I was one of them for 6 years) just don't have the patience to deal with the endless barage of "expert" consumers asking for justification to spend money at their stores. The guys "in the back" get burnt out on day to day interaction with people, thats why they are "in the back."

I sympathize with both you and them. They know that Dura Ace 10 will work with ALL Dura Ace 10 speed equipment. They don't want to find out if you can leave out one link in the "chain".

-SD

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https://www.kickstarter.com/...bike-for-the-new-era

I can empathize with the mechanics, I too was one for a couple of years, and people that really do not want to have much interaction.

However, I (like a lot of people, I think) just like to know "why" on certain things. Its just the way I learned as a kid, I drove my math and science teachers nuts when I would not just accept theories and formulas.

How do you know this--in other words, how do you know that it is the "extra" float on the 9-spd deraill. that is the source of the shifting problem vs. something else causing the problem?

So, if I understand your answer correctly, if the 9-spd deraill. did not have an upper pulley with the greater float, then it should work perfectly well with a 10-spd cassette, 10-spd chain, and 10-spd shifters, yes?

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I've investigated the matter fully with Shimano tech support and used my experience in the field to draw that conclusion.

So, if I understand your answer correctly, if the 9-spd deraill. did not have an upper pulley with the greater float, then it should work perfectly well with a 10-spd cassette, 10-spd chain, and 10-spd shifters, yes?

That is correct. If the ENTIRE derailleur cage of the 9 speed derailleur were replaced with the 10 speed cage somehow, it would function perfectly. There is no difference in the geometry of the cable pull requirement like an above post mentioned.

-SD

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https://www.kickstarter.com/...bike-for-the-new-era