SRAM rear mech with Shimano 105?

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Hoggy1972
Posts: 2
Joined: 5 Feb 2019, 10:45pm

SRAM rear mech with Shimano 105?

Postby Hoggy1972 » 5 Feb 2019, 10:56pm

Hi,

Just joined the forum and i'm keen for some advice. I currently run a Ribble Sportive Bianco with a Shimano 105 5700 (10 Speed) groupset. Its got a 50/34 chainset and a 12-28 cassette, with a standard shortcage rear mech.

I'm doing some big sportives in the coming months and want to change the cassette for a 12-30 or even 32 but i don't think my rear mech will handle it as its very stretched on the 28 cog. I do have a spare, lightly used, 9 speed SRAM X5 MTB rear mech with a long cage, and i wondered whether this would work with the 10 speed 105 shifters. I think i read somewhere that a 10 speed SRAM mech would not work because of different actuation ratios, but a 9 speed would work. Is that right?

Any advice welcome :)

Cheers.

thelawnet
Posts: 1639
Joined: 27 Aug 2010, 12:56am

Re: SRAM rear mech with Shimano 105?

Postby thelawnet » 6 Feb 2019, 12:58pm

No, it won't work, the Shimano derailleur has a 1.7 pull ratio, the SRAM has a 1:1 ratio.

However you can just fit a RD-5701-GS, which is officially rated for 12-32.

http://www.premium-comfort.com/content/ ... -gs-l.html

And your existing mech is specced for 12-30 so it should work.

http://www.shimano-nordic.com/content/s ... -ss-l.html

Brucey
Posts: 32274
Joined: 4 Jan 2012, 6:25pm

Re: SRAM rear mech with Shimano 105?

Postby Brucey » 6 Feb 2019, 1:23pm

a 9s shimano mech will work with your shifters and a 10s cassette. Since this includes 9s shimano MTB mechs you can easily get one that has enough capacity for a 36t sprocket if you want to. You can still buy mechs such as XT 9s RD-M772 and they work really well.

Two wrinkles;

1) not all MTB mechs have barrel adjuster built in; (you may have one on the DT or be able to fit an inline adjuster)
2) you will need a longer chain than with a short-arm mech.

cheers
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Hoggy1972
Posts: 2
Joined: 5 Feb 2019, 10:45pm

Re: SRAM rear mech with Shimano 105?

Postby Hoggy1972 » 6 Feb 2019, 4:15pm

Thanks, so i have seen this one

https://www.ebay.co.uk/itm/Shimano-XT-M ... ctupt=true

would that suit? How long does the chain need to be? I have been looking at chains and they all seem to be 114 or 116 links. Is there a guide which says how many extra links does the chain need for each extra tooth on the back.

Brucey
Posts: 32274
Joined: 4 Jan 2012, 6:25pm

Re: SRAM rear mech with Shimano 105?

Postby Brucey » 6 Feb 2019, 5:51pm

Hoggy1972 wrote:Thanks, so i have seen this one

https://www.ebay.co.uk/itm/Shimano-XT-M ... ctupt=true

would that suit? How long does the chain need to be? I have been looking at chains and they all seem to be 114 or 116 links. Is there a guide which says how many extra links does the chain need for each extra tooth on the back.

RD-M771?
that is a low normal mech. You don't want that, not if you are used to working the gears in a normal way (most mechs are high normal).

The extra chain you need is about

- 2 extra half-links per four teeth extra on the rear sprocket (so say 116L instead of 114L if going from 28T to 32T) and

- 2 extra half-links per inch the cage is longer.

You also need to correct for pulley size but I am assuming the new and old mechs have 11T pulleys.

cheers
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~~~~~~~~~~~~~~~~~~~~~~Brucey~~~~~~~~~~~~~~~~~~~~~~~~

thelawnet
Posts: 1639
Joined: 27 Aug 2010, 12:56am

Re: SRAM rear mech with Shimano 105?

Postby thelawnet » 6 Feb 2019, 6:03pm

Hoggy1972 wrote:Thanks, so i have seen this one

https://www.ebay.co.uk/itm/Shimano-XT-M ... ctupt=true

would that suit? How long does the chain need to be? I have been looking at chains and they all seem to be 114 or 116 links. Is there a guide which says how many extra links does the chain need for each extra tooth on the back.


I buy 110 link chains, which are exactly the right length for the 40/36 gear on my mountain bike. 114 links would be more than sufficient with a bigger chainring.