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9s BE for 7s DA?

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9s BE for 7s DA?

Old 03-28-17, 11:03 PM
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mountaindave 
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9s BE for 7s DA?

I have a secret desire to try a nearly full DA build for a 7 speed setup but using bar ends. I just missed out on what could have been a perfect bar end combo on eBay : someone put a 7s Dura Ace DT shifter onto a bar end pod. Oh well.

So going over the glorious Sheldon Brown cassette crib sheet (for the millionth time), I am confident that 7s and 8s cassette spacing are identical. Literature states, and I personally know, that a 9s bar end will flawlessly shift a 7400 DA RD with an 8s cassette (currently doing so on a bike). Combine the two concepts and one should be able to use the same 9s bar end to shift a 7s cassette pulling a 7400 Dura Ace RD. Two "clicks" won't be used, but they don't matter.

Am I crazy? Has anyone tried this?

Thanks in advance.
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Old 03-29-17, 04:12 AM
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mountaindave, While not identical, the spacing of the 7S and 8S cassettes are close enough to mix and match non DA indexed shifters with non DA RDs IME. To use the 74XX series RD with a non 74XX series indexed shifter requires any 9S Shimano indexed shifter, per Shimano.

I think it should work, let us know.

Brad
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Old 03-29-17, 04:51 AM
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Those were my thoughts in a nutshell.
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Old 03-29-17, 08:10 AM
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This isn't what you're after, but..

I've been using a 7402 rear derailleur with a 9 speed cassette and 8/9 Dura Ace bar ends for a couple years now, without any issues.
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Old 03-29-17, 12:58 PM
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Interesting.
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Old 03-29-17, 02:23 PM
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Originally Posted by mountaindave View Post
Interesting.
Indeed. First off, there is no such thing as 8/9 speed shifters - the spacing is completely incompatible. Second, I assume you want crisp, precise indexed shifting, and not a derailleur randomly jumping between cogs, and constantly clattering away in every gear. This is what most of the riding public seems to think is 'normal' drivetrain behaviour. Third: running in friction does not count, and is not responsive to your question.

So to your question: running the math, 9-speed Shimano shifters (STI or bar-ends, regardless of the Shimano model) will index correctly here.

The shifters pull 2.6mm of cable per 'click'. Dura-Ace 7400 derailleurs have a mechanical actuation of 1.84. 2.6 x 1.84 = 4.78mm. Shimano 8-speed cog spacing is 4.80mm. So this will work perfectly with Shimano 8-speed, and also acceptably a 7-speed cogset, which has a 5.0mm cog spacing.

If the shifting seems a bit fussy, then replace a few of the 7-speed spacers with the slightly narrower 8 speeders.
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Old 03-29-17, 03:07 PM
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Originally Posted by Dave Mayer View Post
Indeed. First off, there is no such thing as 8/9 speed shifters - the spacing is completely incompatible.
Wrong

These are 8 and 9 speed compatable. I've had them in both applications, and they shift fine for each.

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Old 03-29-17, 05:34 PM
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Well, those are both 8 and 9 speed shifters only because they are compatible with two different shift ratio RD's. The 7400 RD has a shift ratio of 1.9 and any other semi-modern shimano RD (excluding 11 speed which is around 1.37) has a shift ratio of 1.7. The 2.5mm cable pull just happens to work out as 8 speed cassette spacing via a 7400 RD, but would be 9 speed cassette spacing with a modern shimano RD such as a 6500 ultegra.

If you tried to use a 6500 RD with those shifters and shift 8 speed, the results would be pretty lousy as you'd be under shifting by .25mm each shift. Even if centered on one of the middle cogs you'd be off a full mm at the end of the cassette which more than likely would be unacceptable. I recall having tried between 8 and 7 with a modern shimano RD and that was not acceptable either using 8 speed shifters.
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Old 03-29-17, 05:45 PM
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And here's a crib sheet, if anyone can read it...
Attached Images
File Type: jpg
IMG_3199.jpg (96.0 KB, 41 views)
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Old 03-29-17, 10:24 PM
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I can't quite read it, but have I seen that spreadsheet somewhere online before? Is there ever a better time than when C/Vers geek out together?

I have above posted 8s(7400)/9s(7700) bar ends. They work beautifully with 8s 7400 kit.

I like the idea of using 8s sprockets/spacers where I can. Only the 1st and 2nd position sprockets may be odd (can't recall if they are 8s specific or not) on my 7400 hub.
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