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Ultegra 6500 RD vs Dura ace RD 7900

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Ultegra 6500 RD vs Dura ace RD 7900

Old 05-02-20, 08:29 PM
  #1  
FM Jump
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Ultegra 6500 RD vs Dura ace RD 7900

I cant seem to figure out if I can replace my 9 speed Ultegra 6500 RD with a Dura Ace10 speed 7900 RD.
Ive got one day to buy one on ebay. Anybody know?
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Old 05-02-20, 11:24 PM
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Not unless you intend to replace your shifters as well.
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Old 05-02-20, 11:55 PM
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I was under the impression that the rear derailleur doesn’t care if the shifter is 9 or 10 speed (?)
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Old 05-03-20, 01:40 AM
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In some cases that is true. It's more the exception than the rule, however. In your specific case, your 9 speed shifter will not work with the Dura Ace 10 speed RD.
I stand corrected. Editing to prevent propagation of inaccurate info while preserving the context of the thread.

Last edited by tFUnK; 05-04-20 at 01:13 AM.
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Old 05-03-20, 05:12 AM
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My understanding is that Shimano pull ratio remained the same for road components through 10 speed, so the 7900 rear derailleur should work with the 6500 shifter. There were some oddball Dura Ace pull ratios in the past, but 7900 used the same 1.7 as the 9 speed road groups. I believe the brake pull leverage was changed, but that won't matter in the OP's case.
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Old 05-03-20, 08:31 AM
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Well you're both senior members so each of you must have experience and your reasoning however I'm still confused :/
I tried looking it up and also got conflicting information. I wish I knew someone who actually tried it.
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Old 05-03-20, 08:51 AM
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It will work. Both have a 1.7 pull ratio. Here is a chart that a member here (Sorry can't remember who) generously donated. Scroll down to the proper year designation and find your derailleurs. 6500 is from 1998 and 7900 is 2008. https://docs.google.com/spreadsheets...#gid=847158527

Last edited by Crankycrank; 05-03-20 at 08:55 AM.
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Old 05-03-20, 08:59 AM
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According to THIS SITE, the cable pull is different between Shimano 9 and 10 speed shifters. The derailleur ratio is the same (1.7), but since the cable pull is different, the derailleur movement won't match the cassette (if I understand the math here).
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Old 05-03-20, 09:04 AM
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Originally Posted by sweeks View Post
According to THIS SITE, the cable pull is different between Shimano 9 and 10 speed shifters. The derailleur ratio is the same (1.7), but since the cable pull is different, the derailleur movement won't match the cassette (if I understand the math here).
That site is full of errors but, in this case, you are mistaken about the math. The difference in the amount of cable pulled by the shifter is what allows one to shift 9 speeds and the other 10 speeds with the same pull ratio.

Last edited by dsaul; 05-03-20 at 09:08 AM.
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Old 05-03-20, 09:10 AM
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Originally Posted by dsaul View Post
that site is full of errors but, in this case, you are mistaken about the math. The difference in the amount of cable pulled by the shifter is what allows one to shift 9 speeds and the other 10 speeds with the same pull ratio.
+1.
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Old 05-03-20, 09:23 AM
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It seems to make sense that if the cable pull is different than the RD wouldnt travel correctly per shift. BUT, many people say it works. Ugh.
Thanks everyone for commenting. I will try it and post my results here in about 2 weeks.

Last edited by FM Jump; 05-03-20 at 09:29 AM.
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Old 05-03-20, 09:40 AM
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Originally Posted by FM Jump View Post
It seems to make sense that if the cable pull is different than the RD wouldnt travel correctly per shift. BUT, many people say it works. Ugh.
If the rear derailleurs have the same pull ratio of 1.7, the only way to change the number of gears it shifts is to change the amount of cable the shifter pulls with each shift. The cogs are closer together in a 10 speed cassette, so the 10 speed shifter pulls less cable to match the cog spacing. Your 9 speed shifter will pull the correct amount of cable to match the 9 speed cassette spacing. As long as the cassette and shifter are both the same speed(9 or 10) it will work fine.
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Old 05-03-20, 09:55 AM
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Originally Posted by FM Jump View Post
It seems to make sense that if the cable pull is different than the RD wouldnt travel correctly per shift. BUT, many people say it works. Ugh.
Thanks everyone for commenting. I will try it and post my results here in about 2 weeks.
And just to add another bit of validation. I and many others here use mixed derailleur-shifter groupsets with NO issues as long as the DERAILLEURS have the same pull ratio. I'm running a 6500 derailleur with 6600 10sp shifters. Just needed to match the cassette speeds with the shifters. Very simple.
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Old 05-03-20, 10:28 AM
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I have a feeling its gonna work out fine, and I will absolutely let everyone know here. Sheldon wrote about wrapping the RD cable in an alternate fashion to make it compatible. I will try that after I win the RD on ebay in about 30 minutes.
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Old 05-03-20, 10:59 AM
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Originally Posted by dsaul View Post
That site is full of errors but, in this case, you are mistaken about the math. The difference in the amount of cable pulled by the shifter is what allows one to shift 9 speeds and the other 10 speeds with the same pull ratio.
I understand that. I was under the impression that the OP wanted to retain the 9-speed shifter and use a 10-speed cassette. The derailleur would still move the same amount as it should for a 9-speed cassette, wouldn't it? The 1.7 ratio is the distance (in mm) the derailleur moves for each mm the cable moves. So how does the 9-speed shifter provide the right amount of derailleur travel for 10 speeds?
I have no particular confidence in the site I linked; it showed the same derailleur ratio and different cable pull, which seemed to be the relevant numbers.
EDIT: Wouldn't this be the same issue if the OP put the 10-speed cassette on with the original 9-speed shifter and derailleur?
EDIT: In other words, what dsaul said in post #12 .

Last edited by sweeks; 05-03-20 at 11:04 AM.
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Old 05-03-20, 11:16 AM
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Originally Posted by sweeks View Post
I understand that. I was under the impression that the OP wanted to retain the 9-speed shifter and use a 10-speed cassette. The derailleur would still move the same amount as it should for a 9-speed cassette, wouldn't it? The 1.7 ratio is the distance (in mm) the derailleur moves for each mm the cable moves. So how does the 9-speed shifter provide the right amount of derailleur travel for 10 speeds?
I have no particular confidence in the site I linked; it showed the same derailleur ratio and different cable pull, which seemed to be the relevant numbers.
EDIT: Wouldn't this be the same issue if the OP put the 10-speed cassette on with the original 9-speed shifter and derailleur?
EDIT: In other words, what dsaul said in post #12 .
My understanding of the OP was that he was just replacing the rear derailleur and keeping everything else the same.
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Old 05-03-20, 11:18 AM
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What's wrong with the Ultegra RD? I'd be inclined to replace like for like if something is wrong with the one currently in use.
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Old 05-03-20, 11:22 AM
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I am only replacing the 6500 RD. Everything else works fine as a 9 speed Ultegra system. I lost the ebay auction though. I will have to try again on another.
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Old 05-03-20, 11:29 AM
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It will work just fine, in my experience. In fact, I’ve used a 7900 shifter to motivate a Shimano 600 6208 RD to shift a ten speed cassette. That’s the earliest normal (non-740X DA) derailleur they made.
So yeah, all that Shimano 6-7-8-9-10 speed 105-600-Exage Light Action- RX100-Ultegra-Dura Ace 7700,7800,7850 and 7900 road stuff, again with the exception of DA 740X, is forward and reverse compatible.
Most of the early Sora and Tiagra (not the newer) and 6-7-8-9 speed Deore as well.
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Old 05-03-20, 12:18 PM
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Originally Posted by dsaul View Post
My understanding of the OP was that he was just replacing the rear derailleur and keeping everything else the same.
I see by post #18 that you are correct. I was misled by post #3 ("I was under the impression that the rear derailleur doesn’t care if the shifter is 9 or 10 speed (?)" ).
The confusion was all mine.
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Old 05-03-20, 01:21 PM
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Originally Posted by FM Jump View Post
Sheldon wrote about wrapping the RD cable in an alternate fashion to make it compatible.
The alternate cable theory is fascinating and fun when all things come together; I have used it on older Dura Ace. If I had machining facilities, I would probably push the alternate attach points just to see what would happen.

Sadly you will not be able to experience it as it will be plug and play and work as it was designed.

John
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Old 05-03-20, 03:05 PM
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Originally Posted by 70sSanO View Post
The alternate cable theory is fascinating and fun when all things come together; I have used it on older Dura Ace. If I had machining facilities, I would probably push the alternate attach points just to see what would happen.

Sadly you will not be able to experience it as it will be plug and play and work as it was designed.

John
Thats encouraging. Thanks
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Old 05-04-20, 01:11 AM
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Originally Posted by dsaul View Post
There were some oddball Dura Ace pull ratios in the past, but 7900 used the same 1.7 as the 9 speed road groups. I believe the brake pull leverage was changed, but that won't matter in the OP's case.
This was what I had in mind when responding initially. Thanks for this clarification. I am happy to stand corrected.

Last edited by tFUnK; 05-04-20 at 01:15 AM.
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Old 05-04-20, 01:17 AM
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I am questioning the chain though. I use a 9 speed Shimano chain and the DA 7900 groupset uses a 10 speed asymmetrical chain. Not sure if it will mean anything since its only the jockey wheels being affected because everything else is Ultegra 6500.
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Old 05-04-20, 04:06 AM
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Originally Posted by FM Jump View Post
I am questioning the chain though. I use a 9 speed Shimano chain and the DA 7900 groupset uses a 10 speed asymmetrical chain. Not sure if it will mean anything since its only the jockey wheels being affected because everything else is Ultegra 6500.
My 9 speed Deore MTB derailleur doesn't care that I run 10 speed chain through it, so I doubt the 7900 will care about 9 speed chain. Seriously though, there was nothing special about the 7900 drivetrain that required an asymmetrical chain. I had that groupset and ran KMC chains after discovering that Shimano's experiment with their own version of a quick link on Dura Ace chains resulted in that link stretching and causing an annoying click in the drivetrain every time it passed over the cassette.
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