RD for 105 / DA groupset

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fredN4
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RD for 105 / DA groupset

Postby fredN4 » 13 Mar 2019, 8:54am

Morning folks
I am in process of buying a road bike for my daughter-in-law who lives in hilly Bath. The bike I have found is a LOOK 555 of about 10 years old. It has 105 shifters with DA front and rear derailleurs. It is 10 speed. Chainset is a compact 50/34. All works well. I wish to fit an 11-34 cassette. I have read that a DEORE M591 9 Speed will do the business. Any thoughts or advice would be welcome.
Regards
Fred

Brucey
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Re: RD for 105 / DA groupset

Postby Brucey » 13 Mar 2019, 8:56am

yep, any 9s shimano MTB mech will work with those shifters. Also some 10s 'road' RDs have enough capacity for a 34T sprocket, but don't get a 4700 tiagra one; it has a different shift ratio.

Bath is indeed hilly.

cheers
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fredN4
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Re: RD for 105 / DA groupset

Postby fredN4 » 13 Mar 2019, 10:07am

Thanks Brucey. Nice to see you are still around! Could you say which road 10 RDs would work? I knew about Tiagra 4700 (just in time!)

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Mick F
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Re: RD for 105 / DA groupset

Postby Mick F » 13 Mar 2019, 10:20am

I have a Deore XT long cage on my Moulton.
Absolutely excellent rear mech.
https://www.wiggle.co.uk/shimano-xt-m77 ... erailleur/
At that price, I may buy a spare!
Mick F. Cornwall

Brucey
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Re: RD for 105 / DA groupset

Postby Brucey » 13 Mar 2019, 11:10am

fredN4 wrote:Thanks Brucey. Nice to see you are still around! Could you say which road 10 RDs would work? I knew about Tiagra 4700 (just in time!)


Most of the last generation of 10s road mechs will work (4700 asides) in that they will usually accept a 34T sprocket (unless the gear hanger is unusually short) despite what the official shimano specs say [for example RD-5701-GS has an official max sprocket of 32T]. However not all have a long enough arm to take up all the chain slack from a 16T difference compact double and a 34T sprocket. Also not all frames allow enough B screw movement, so sometimes an adaptation is required here.

A 9s MTB mech is a much safer choice, capacity-wise; they are meant for 34 or 36T sprockets (depending on the model) and have the correct shift ratio. Just make sure that you have a barrel adjuster somewhere in the cable run; some 9s RDs don't have one on the mech itself.

BTW RD-M772 would be my choice too.

cheers
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fredN4
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Re: RD for 105 / DA groupset

Postby fredN4 » 13 Mar 2019, 11:23am

thanks again folks

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The utility cyclist
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Re: RD for 105 / DA groupset

Postby The utility cyclist » 13 Mar 2019, 2:29pm

Shimano RD-6700-A SS, which is the later incarnation short cage could according to the tec specs handle a 30T max sprocket (the earlier one was only 28T), I know for a fact that the next gen 6800 SS will handle a 32T sprocket, I run this on my specialized sirrus full carbon gravel bike and quite a few other people have done this with the first 11 speed short cage RD.

However the max sprocket size did NOT increase for the RD-6700-A GS/long cage variant (according to the specs), it was simply about increasing the total capacity. Though I have the GS variant I run it with a triple so haven't as yet had to test it with a really big sprocket - I did buy a 12-36 10 speed just in case I decided to go loaded touring in the mountains but I'm not a mountains person so I've not tested it with the longer cage road mech.

The length of the derailleur hanger will also have a subtle effect too on what's possible, here is a link to a forum where a LOOK 566 owner runs a 32T big sprocket, scroll down to the bottom https://www.bikeforums.net/bicycle-mech ... acity.html

Given that the higher end long cage 10 speed road mechs are in shorter supply and not that cheap compared to 9 speed MTB mechs, I would er on the side of getting the MTB mech and know for absolute sure that it would take the 34T.

All that said, if you want to try to avoid the problem altogether AND reduce the even bigger jumps of using a 34T sprocket and give easier transition when going up/down the range, I would simply buy a 33T inner ring (TA make these and you can buy them for under £22), with a 32T sprocket this would only be 0.8" gear inch higher than a 34/34.
Then you could buy a 12-32, which narrows the jumps even more and the oft unused 11T sprocket is removed from the equation. If you're going to have to buy a new RD and a cassette anyways then why not try options that might work out cheaper (£22 v new rear derailleur) whilst having better/easier ratio jumps.
Lastly, also though may not ever happen, it will avoid a big/big 50x34 combination which may well be too much for the chain fitted if the user accidentally does this, I appreciate it's only a 2 tooth difference but that can be the difference between a mechanical and not.

HTH
Last edited by The utility cyclist on 13 Mar 2019, 4:33pm, edited 1 time in total.

thelawnet
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Re: RD for 105 / DA groupset

Postby thelawnet » 13 Mar 2019, 2:42pm

Brucey wrote:BTW RD-M772 would be my choice too.


Is that better than a cheapo r-d

https://www.bike-discount.de/en/buy/shi ... ountry=190

and a set of the same jockey wheels from the M772?

https://www.bike-discount.de/en/buy/shi ... els-534918

Brucey
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Re: RD for 105 / DA groupset

Postby Brucey » 13 Mar 2019, 2:50pm

probably yes, but whether it is worth the difference is debatable...

cheers
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Mick F
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Re: RD for 105 / DA groupset

Postby Mick F » 13 Mar 2019, 3:00pm

The top pivot is the big killer of a rear mech. The Tiagra went the same way as my Campag Chorus rear mech. Yes, you can stuff some PTFE tape in there to help, but the big problem - like I said - is the top pivot. Eventually it will kill the rear mech shifting as it'll flop in and out.

The RD-M772 is a "shadow" system in that it doesn't have a top pivot. Same as the Altus one linked above.
Brilliant design, but the Deore XT is a nicer one than the Altus.
Mick F. Cornwall

thelawnet
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Re: RD for 105 / DA groupset

Postby thelawnet » 13 Mar 2019, 3:57pm

FWIW, the current Shimano catalogue reckons there are six current 9-speed MTB rear derailleurs. There are other, old model numbers that are probably identical in design.

M772 Deore XT, Shadow, 36t max
M592 Deore, Shadow, 36t max
M591 Deore, non-Shadow, 34t max
M4000 Alivio, Shadow, 36t max
M3000 Acera, Shadow, 36t max
M2000 Altus, Shadow, 36t max

The Altus uses a solid non-removable B axle unit, whereas the others have hollow removable B axles allowing them to be used with direct mount frames. The XT derailleur is also mostly aluminium and presumably lighter than the others.

They also provide that XT has 4 'fluoric coated link bushings', Deore has 3, Alivio 2, Acera 1, and Altus 0.

I am not clear the significance of this.

The 9-speed era XT jockey wheels use a sealed bearing for the tension pulley and a sealed ceramic bushing for the guide pulley.

Image

Sealing seems to be quite important for jockey wheels if you are in bad weather, though I guess you could always pack cheap ones with grease.

The 9-speed XTR jockeys got this supposedly mud-shedding design on the tension pulley

Image

This was brought to XT

Image

10-speed XTR and Saint were given the mud-shedding on the guide AND tension pulleys.

Image

This is now standard on 11-speed XT as well

Image

The sealed bearing tension pulley is common but there are different version of bushing vs bearing for the guide pulley even with similar wheel designs. No idea which works better or whether the wheels can be switched successfully.

Brucey
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Re: RD for 105 / DA groupset

Postby Brucey » 13 Mar 2019, 7:58pm

Re RD capacities for 10s shimano road systems:

through most of the 10s era Shimano only produced 10s 'road' cassettes with sprockets up to 28T. It never occurred to them that you might want lower gears on a road bike; after all they had just launched 110mm BCD road double chainsets and who would want a gear lower than 34/28 on a road bike? If you did there was always the option of a triple chainset. So their RD specs all read '28T maximum sprocket' whether that was a real reflection of the RD's capacity or not. Obviously folk did want to have larger sprockets and tried to find ways of nailing MTB cassettes into a road system.

Shimano probably lost sales to SRAM around this time because it was easier to be sure that you would have a system that actually worked; SRAM's mechs worked with the same pull ratio between 10s MTB and 10s road. You could make a shimano system work but it seemed weird, having to fit a '9s' MTB RD to a 10 system...

Anyway quite late on in the day (when DA and Ultegra had gone to 11s) shimano woke up and started producing larger range 'road' cassettes in 10s and in 105 the RD-5701 rear mechs suddenly had 'more capacity' than the preceding 5700 models.

Image
RD-5700-GS (allegedly)

Image
RD-5701-GS (allegedly)

yes folks, it is strangely difficult to tell these RDs apart. Possibly there is some subtle difference between them (like the springs?) but even with then two of them in your hand it is difficult to see it.

Note also that the specification for RD-5701-GS is different from that of RD-5700-GS in that instead of flatly saying '28T max' it says something more subtle than that, i.e. that if you use a triple with up to 22T front difference, they say 30T sprocket is your lot, but if you use a front double with 16T difference, you can have a 32T sprocket. This is interesting on several counts;

1) this is in fact what happens with RDs; the max sprocket size and total capacity (front capacity) are not unrelated (MTB specs have read this way for years)....RD-5701-GS specification is more realistic, and isn't obviously so influenced by what cassettes shimano have bothered to make this week and

2) the RD 'doesn't really know' what size chainrings you are using; you can usually get away with more than they say you can, provided you are careful about setup and don't just throw the bike together. For example tolerating slack running in the small-small combination is usually quite acceptable.

3) Shimano specifications are conservative; going from 32T to 34T needs just another ~4mm clearance. Often just twirling the B tension screw gets you that. There are plenty of folk using RDs with wolf tooth hanger extenders etc and the RDs are way out of their alleged comfort zone.

so anyway it is always worth a go, trying to see if a certain combination will work or not. It is usually pretty clear on the workstand if it isn't going to work, you don't have to find out the hard way...

cheers
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thelawnet
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Re: RD for 105 / DA groupset

Postby thelawnet » 13 Mar 2019, 10:21pm

Brucey wrote:yes folks, it is strangely difficult to tell these RDs apart. Possibly there is some subtle difference between them (like the springs?) but even with then two of them in your hand it is difficult to see it.


Not clear?

5701 spring:

Image

5700 spring:

Image

FWIW as you say the specs can be a bit prescriptive in terms of specific Shimano cassettes/chainrings as opposed to actual capacities.

The spec for the aforementioned RD-M772 currently is:

11-32 to 11-36, max front difference 22t

with a total capacity of 45t for long cage, and 35t for mid cage

Whereas originally when Shimano didn't sell 11-36t, they said

11-32 to 11-34 with the same capacity and front difference.

They didn't however bump up the pre-Shadow derailleurs to 11-36t, but that doesn't necessarily mean that a non-Shadow 9-speed MTB RD is worse with 11-36 than a Shadow one, it could just be they haven't bothered to updae it.

Incidentally the capacity numbers are a bit confusing - if the total capacity is 35t, you've got a minimum cassette size of 11-32 (21t) and a maximum of 11-36t (25t), then that makes a front difference of between 10t and 14t. But they say 'max front difference 22t', but if the front difference was 22t, you'd only be able to manage an 11-24t at the back.

It seems they are just wrong.

Presumably it should say 'max front capacity' 14t.

Shimano's 11-speed MTB RDs are now all designed for dinner-plate-sized cassettes, but the 10-speed Shadow derailleurs have a choice of types:

short cage single x 11/12-23t-36t (capacity 25t)
mid cage double x 11-32 to 11-36 (capacity 35t)
mid cage double x 11-42 (capacity 41t)
long cage triple x 11-32 to to 11-36 (capacity 43t)

The distinction between the 'mid' cage for the 11-42t and the long cage for the 11-36t is apparently that the long cage isn't designed to clear the 42t tooth, even though it has a slightly higher total capacity.

However you can find bikes like this one

https://www.polygonbikes.com/shop/bikes ... ntiat-tr6/

with a 1x 11-42t 10-speed drivetrain and the first type (11-36t 35t capacity) of mid cage derailleur fitted from the factory. It's not really clear to what extent the newer 41t mid cage capacity would shift better for that particular bike, nor indeed how much better the new 'mid cage' 10-speed RD with a 38/28 x 11-42t is than the same setup with the long cage.

At least if you respect 'total capacity' somewhat it has a good chance of working

geocycle
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Re: RD for 105 / DA groupset

Postby geocycle » 14 Mar 2019, 8:47am

This is a really interesting if very complicated thread! So I have an 11 speed 105 groupset with 50-34 at the front and 11-32 at the back. I'm not entirely sure which rear105 derailleur. The 11 tooth sprocket is an ornament in the Lake District and a 34 or even 36 tooth sprocket on the cassette would be much more useful. Any suggestions which cassette and which derailleur I would need? Is there a list somewhere?

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Mick F
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Re: RD for 105 / DA groupset

Postby Mick F » 14 Mar 2019, 9:13am

thelawnet wrote:The spec for the aforementioned RD-M772 currently is:

11-32 to 11-36, max front difference 22t

with a total capacity of 45t for long cage, and 35t for mid cage
I'm running my RD-M772 with the following:
11-28 cassette
61/48/34 chainset.

This gives the front difference of 27t
Total capacity of the system is 44t and it ONLY JUST does it.
Very sloppy chain in small/small, and tight in big/big (but it's ok).

If I had a 45t capacity, the small/small would be dangling and swinging.
Mick F. Cornwall