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10 speed shifters with 8 speed derailleurs (upgrading cassette to 10)?

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10 speed shifters with 8 speed derailleurs (upgrading cassette to 10)?

Old 01-12-16, 12:47 PM
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10 speed shifters with 8 speed derailleurs (upgrading cassette to 10)?

Not really practical to do this, but I want to satisfy my curiosity and keep my options open. I think I've seen that you can run different speed components with each other, but haven't seen anything definitive whether I could change shifters to 2x10 speed (namely microshift or if I find shimano stuff cheap on craigslist) and keep my 2x8 speed 105 derailleurs if I swap out the cassette and chain/chainrings (and yes, I have 10/11 speed wheels). If not 10 speed, would 9 speed shifters would (again with the cassette/chain/chainring update)? I'm more focused on getting a new bike in the next year and keeping my current one as a secondary, but I like to consider options if things come up cheaply enough. As I said, I think I've seen conflicting information as to whether something like that can be done
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Old 01-12-16, 12:57 PM
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Yes. A Shimano (and Shimano compatible like Microshift) 10 speed brifter would work with a Shimano 8 speed derailleur. Up until recently Shimano kept these things pretty compatible. Then in the move to 11 speed (and 10 speed on MTB gearing), everything got screwed up. Here's an article with some of the numbers:

Art's Cyclery Blog Science Behind the Magic | Drivetrain Compatibility

You can see that Shimano 6 speed to 10 speed (road) all have the same number for derailleur ratio, which is the magic number in terms of whether the shifter will correctly work with the derailleur.
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Old 01-12-16, 01:21 PM
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Sounds like a lot of work to me, for what purpose? You're talking about changing out almost the entire drivetrain except for the crankset and derailers.

Yes it will work. RD will be fine. FD might be a little slower as the cage will be wider than a 10-speed FD. But it will probably work.

One thing I've done many times is keep the 8-speed cassette and chain but use Campagnolo 10-speed brifters which have the same cable pull as Shimano 8-speed. This lets me keep my entire 8-speed drivetrain which is simple, cheap, and reliable but adds some nice Campy brifters to the cockpit. You can go all the way up to Record!
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Old 01-12-16, 01:56 PM
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All in the dimensions of the RD parallelogram .. distances between pivots ..

Influences how far it moves in for a given cable pull distance.
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Old 01-12-16, 02:52 PM
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A new cassette, chain and shifters will work. The crank is iffy, might work fine or possible have shifting issues. I've had both happen. Cranks aren't too expensive if you need one.
This was 7 speed, now 10 with DuraAce downtube shifters. Took the opportunity to change to a compact crank.

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Old 01-12-16, 04:18 PM
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Originally Posted by FastJake

One thing I've done many times is keep the 8-speed cassette and chain but use Campagnolo 10-speed brifters which have the same cable pull as Shimano 8-speed. This lets me keep my entire 8-speed drivetrain which is simple, cheap, and reliable but adds some nice Campy brifters to the cockpit. You can go all the way up to Record!
+1. Makes a durable rain and winter bike setup with better ergonomics than anything shimano has at 8 speed, with cheaply replaced parts too. You can sometimes run a 10 speed cassette with a campy derailer, but it works slightly better if you use a campy 8 speed derailer. That way you can have a 10 speed shimano cassette but campy shifters. Of course this is all a tangent to the original question.
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Old 01-13-16, 12:45 AM
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Shimano 6-10 speed road shifters work with 6-10 speed road RDs and 6 to 9 speed MTB RDs.

Shimano 6-9 speed MTB shifters work with 6-10 speed road RDs and 6-9 speed MTB RDs.

Shimano 10 speed MTB shifters work with 10 speed MTB RD only.

Shimano 11 speed MTB shifters work with Shimano 11 speed MTB RD only.

Shimano 11 speed road shifters work with Shimano 11 speed road RD only.
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Old 07-12-17, 02:28 PM
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St-4700

The situation has been muddied by the introduction of ST-4700. They combine with 11-speed derailleurs (I regard RD-4700 as an 11-speed derailleur) and 10-speed cassettes. They should also work well with 7-8-9-10-speed derailleurs and 8-speed cassettes, but two outer positions go unused. Similarly, 8-speed shifters should combine well with 11-speed derailleurs and 10-speed cassettes. In this case two cogs go unused which is less fortunate. Anybody care to try some of these combinations?

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Old 07-14-17, 04:25 PM
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Yep
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Old 07-14-17, 05:38 PM
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Originally Posted by Slaninar
Shimano 6-10 speed road shifters work with 6-10 speed road RDs and 6 to 9 speed MTB RDs.
The exception is pre-9-speed Dura Ace rear derailleurs which aren't compatible with other Shimano shifters.

To the OP: I currently have an 8-speed 105 rear derailleur (RD-1056) installed on an otherwise all 10-speed Shimano bike and it shifts just fine.

Last edited by HillRider; 07-14-17 at 05:43 PM.
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Old 07-14-17, 11:28 PM
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Originally Posted by HillRider
The exception is pre-9-speed Dura Ace rear derailleurs which aren't compatible with other Shimano shifters.

To the OP: I currently have an 8-speed 105 rear derailleur (RD-1056) installed on an otherwise all 10-speed Shimano bike and it shifts just fine.
Not sure this is correct. 6-8 speed Dura Ace is the tricky one for all I know. Wrote a list of all the cross-compatibilities for shifters and RDs in these two articles:

7) Bicycle rear shifter compatibility - Cycle Gremlin

4) Bicycle rear derailleur compatibility - Cycle Gremlin

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Old 07-16-17, 07:08 AM
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Originally Posted by Slaninar
Not sure this is correct. 6-8 speed Dura Ace is the tricky one for all I know.
Yeah, that's what I said; pre-9-speed Dura Ace is different.
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Old 07-16-17, 11:51 PM
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Originally Posted by HillRider
Yeah, that's what I said; pre-9-speed Dura Ace is different.
My bad.
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Old 07-30-18, 12:05 PM
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hey I plan to run a 10speed road groupset with mostly 105 5700 parts (50-34 compact crankset) but I dont have a long cage 105 5700 rear derailleur to accommodate a 10 speed Sram 11-32 mtb cassette. Can I use an 8speed mountain bike LX Deore rear derailleur with this set up? Everything else is 105 5700 components.



with 8speed mtb rear derailleur, were there different cage lengths as well? I believe this original 8sp LX deore rear derailleur was paired with a 24 or 25 max 8sp cassette but I dont remember as it has been in my parts bin inventory for a while.

Last edited by Obeast; 07-30-18 at 12:59 PM.
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