STI shifters with a touring crankset

[gloomyandy]

I'm not familiar with the actual parts you are thinking of using, but you may need to use an MTB rear mech of the the total capacity of the road rear mech is not enough to handle the cassette and the chainset you plan to use. Typically MTB rear mechs allow a higher capacity than the road ones.
Total capacity = (cas big - cas small) + (cr big - cr small)
In your case the crankset has a gap of 48-26 = 22 a typical road crankset will have a gap of say 50-34 = 16

[TrevA]

I'm not familiar with the actual parts you are thinking of using, but you may need to use an MTB rear mech of the the total capacity of the road rear mech is not enough to handle the cassette and the chainset you plan to use. Typically MTB rear mechs allow a higher capacity than the road ones.
Total capacity = (cas big - cas small) + (cr big - cr small)
In your case the crankset has a gap of 48-26 = 22 a typical road crankset will have a gap of say 50-34 = 16

If you use a road long arm rear mech designed for use with a triple chainset, then it should have enough capacity. My Tiagra groupset has 52/39/30 rings and a Tiagra long arm mech, which copes with the 22 tooth gap.

[Brucey]

10s STI + 10s cassette/chain + 9s MTB rear mech = functioning 10s system

This works because a 9s mech has the same shift ratio as a 10s (road) rear mech.

[unless the 10s parts are tiagra 4700, which is different]

cheers

Why would a 9 speed rear mech be needed to use an MTB crankset? Surely I can just use the 4700 Tiagra or the 5701 105? I’ll not be fitting an MTB cassette as I’ll stick with road cassette - Most likely Tiagra 11-32/34. The only MTB part I’ll be using is the crankset.

You only need an MTB rear mech if you intend to use an MTB cassette, as many do to get a wide enough range of gears for touring.

I have little doubt that a 10s chain will run OK (maybe not perfectly) on a used 9s MTB chainset but with brand new parts there is a chance that the chain will behave oddly since there is a tiny difference in the internal width of the chain. However this difference is so small that almost any amount of wear is enough to make everything work reasonably well, even it if didn't when all the bits were new. You can fit '10s compatible' chainrings to a 9s chainset but even that does not give you the exact same performance as a dedicated 10s setup, necessarily; the spacing of the chainrings, the nature and alignment of shift ramps etc may not be quite the same, and the chain is narrower externally too. So if you routinely shift under load, etc you might be disappointed but otherwise you might think it is OK.

cheers

[FatLad1980]

Well, this is what I’m considering. Can anyone see any issues with the following setup?

Genesis Tour de Fer 2017 frameset (I already have this)

Tiagra 4700 series shifters

Tiagra 4700 series front and rear mech.

Tiagra 4700 series 11-32/34 cassette

Deore T611 48/36/26 crankset

At 21 stone in weight I’m quite heavy and I’m thinking of loaded touring and hills. Would I perhaps be better off with a Deore 42/32/24 crankset?

[cycleruk]

I did originally try an MTB chainset (Deore M610 48/36/26.) with the 105 5703 front mech'.
I got this to work by out-setting the mech' to make up for the chainline difference.
It worked but never seemed to be sweet so swapped back to the 5703 chainset.

My current set up for my low geared bike.
105 10 speed triple STI
105 10 speed 5703 chainset (50/39/30).
105 10 speed 5703 front dérailleur.
Deore 9 speed rear dérailleur.
Cassette 10 speed (SLX 11-34T)
(I used the SLX because it was on special offer at the time but any 10 speed cassette with up to 34T should work.)

All the above works perfectly and this gives me a low gear of about 24".
The Deore 9 speed "Shadow" is designed to allow a 36T sprocket which would give me a 22" low with the 30T ring.

I do have a 105 triple rear mech' and that, surprisingly, also worked with the 34T cassette.
But as I had the Deore I fitted that and save the 105 for another bike.

I did try smaller granny rings (a 26T and a 28T) on the 5703 crankset but for some reason the chain wouldn't drop onto them cleanly. - Maybe because they are 8 speed ones or some other reason? The drop from the 39T middle ring to the 26T wasn't clean and maybe a chain keeper (dog fang?) would be needed?

The 5703 chainset has a BCD of 74mm for the small ring so will take down to 24T granny ring.
The 5703 also uses standard 5 bolt rings which are commonly available at reasonable prices. That is compared with Shimano's latest 4 arm sculptured rings on their newer chainsets.

[FatLad1980]

The Shimano website lists the 4703 crankset as having a chain line of 43.5 and SJS list the T611 48/36/26 as having a chain line of 50mm? Both the 4703 and 5703 front mechs have a chain line of 45. What would this mean for my intended set up?

[FatLad1980]

I did originally try an MTB chainset (Deore M610 48/36/26.) with the 105 5703 front mech'.
I got this to work by out-setting the mech' to make up for the chainline difference.
It worked but never seemed to be sweet so swapped back to the 5703 chainset.

My current set up for my low geared bike.
105 10 speed triple STI
105 10 speed 5703 chainset (50/39/30).
105 10 speed 5703 front dérailleur.
Deore 9 speed rear dérailleur.
Cassette 10 speed (SLX 11-34T)
(I used the SLX because it was on special offer at the time but any 10 speed cassette with up to 34T should work.)

All the above works perfectly and this gives me a low gear of about 24".
The Deore 9 speed "Shadow" is designed to allow a 36T sprocket which would give me a 22" low with the 30T ring.

I do have a 105 triple rear mech' and that, surprisingly, also worked with the 34T cassette.
But as I had the Deore I fitted that and save the 105 for another bike.

I did try smaller granny rings (a 26T and a 28T) on the 5703 crankset but for some reason the chain wouldn't drop onto them cleanly. - Maybe because they are 8 speed ones or some other reason? The drop from the 39T middle ring to the 26T wasn't clean and maybe a chain keeper (dog fang?) would be needed?

The 5703 chainset has a BCD of 74mm for the small ring so will take down to 24T granny ring.
The 5703 also uses standard 5 bolt rings which are commonly available at reasonable prices. That is compared with Shimano's latest 4 arm sculptured rings on their newer chainsets.

How did you out-set the mech?

[Brucey]

if you are buying new I would suggest that you consider a 9s 'shadow' MTB rear mech and a 36T cassette (although this will necessitate something other than 4700 series STIs). You can fit a smaller inside chainring onto your triple if you want, at a later date, if the gears are still not low enough.

Commonly 'road triple' FDs controlled by STIs won't play well with MTB chainsets. There are several potential issues including that;

- the FD won't reach out far enough to allow the big ring to be selected
- the shifts don't line up properly because the shift ratio of the FD varies with chainline
- the FD isn't designed for the chainring intervals in use
- the 'tail' of the FD hits the chainstay (more likely with a 42T big ring)

The first two can often be addressed by buying an FD to fit the largest possible seat tube, then mounting it on a frame with a smaller seat tube, using an eccentric shim. Some retailers (SJS?) stock an eccentric shim for exactly this purpose.

cheers

[cycleruk]

The Shimano website lists the 4703 crankset as having a chain line of 43.5 and SJS list the T611 48/36/26 as having a chain line of 50mm? What would this mean for my intended set up?

As you may be aware chainline is measured from the centre of the seat tube to the middle ring of the triple. So the figures above would mean that the MTB rings are 6.5mm further away from the bike.
A standard road front mech', fitted normally, would have trouble pushing the chain up onto the big ring as well as being misaligned for the other rings.
I fitted my 105 mech' by using an oversize braze-on clamp with an eccentric spacer to off-set the mech' further out.
Similar idea to this but home made :-
https://www.sjscycles.co.uk/gear-spares ... hed-split/

Although this worked it probably needed to be further out than I could make it to function spot on.
So the theory is if you fit the road mech' further out by 1/4" then it should work?

Unfortunately Shimano don't make (AFAIK) a road chainset with MTB size rings.
The only reasonable confident set-up is to use a square taper BB with a crankset, that such as Spar and others supply, with the ring sizes you require..

EDIT: I see Brucy posted while I was typing with some of the concerns involved.

[freeflow]

I use an XT deore 9 speed 44/32/22 chainset with 105 5703 STI. The front mech is a standard ultegra 6703 and the rear mech is an XT 772 9 speed shadow deraillier and 12-36 10 speed sram cassette. I use SRAM 1051/31 chains. Microshift also do a triple front mech that is a virtual clone of 6603/6703 front mechs (have a look on ebay) - I bought in advance so have two shimano triple front mech and one Microshift in storage.

You will need some spacers/washers to pad out the bottom bracket as the XT chainset is expecting a 73 mm BB not 68 mm.

My rear wheel is 135 mm spacing.

You may need to set your front mech quite high in relation to the big chain ring to avoid hitting the chainstay when on the smallest chainring (my setup has at least a 12 mm gap not the 1-3 mm recommended by Mr Shimano)

You may lose the ability to double click the front mech and may have to resort to click <123> <click> to avoid crunching the chain. It only happens occasionally but is very noisy and worrying if it does. Never happens with single clicks (by doube clikc I mean change from biggest to smallest or vice versa)

You need to accept that it may work for me because of the specific configuration of my frame hence it may not work for you.

I've used this setup for the past three years including a double RRTY in 2015/16 without any significant issues other than mentioned above.

[FatLad1980]

if you are buying new I would suggest that you consider a 9s 'shadow' MTB rear mech and a 36T cassette (although this will necessitate something other than 4700 series STIs). You can fit a smaller inside chainring onto your triple if you want, at a later date, if the gears are still not low enough.


cheers

This was my other thought if my first idea didn’t work. I could have swore I read further back that a 9 speed rear mech works with 10 speed cassettes so why couldn’t I use the 4700 series STI’s?

Is it possible to fit a 26/28T ring in place of the 30 on the 4703 crankset?

[gloomyandy]

4700 series STI's are "special" and have a different cable pull (same as 11 speed I think).

I've also managed to get a road front mech to work on a MTB triple, without any spaces. It was very fiddly though and required things to be at exactly the right height so that the chain sat in the shaped plate (inner I think) when in the middle ring. But it works pretty well.

[Brucey]

This was my other thought if my first idea didn’t work. I could have swore I read further back that a 9 speed rear mech works with 10 speed cassettes so why couldn’t I use the 4700 series STI’s?

The 4700 system is an oddball one that uses a different shift ratio to the other 10s road systems (and 6,7,8,9s systems bar 6,7,8s Dura Ace). For shifters and rear mech to shift the correct (intended as per the shifters) number of sprockets the shift ratio has to match. The rear shift ratio (but not the cable pull) is matched between tiagra 4700 and 11s road systems, which means that you could fit an 11s road mech into a tiagra 10s system and it would still work OK.

I repeat; for a 10s system to work with a 9s rear mech you need any 10s STIs other than 4700.

Is it possible to fit a 26/28T ring in place of the 30 on the 4703 crankset?

Not easily perhaps; the BCD is 74mm (which is small enough) but the pattern is an unevenly spaced 4-bolt one for which there may not be alternative rings.

cheers

[FatLad1980]

4700 series STI's are "special" and have a different cable pull (same as 11 speed I think).

I'm pretty special too......special needs for even attempting this and going as far as ordering the MTB crankset.

[FatLad1980]

This was my other thought if my first idea didn’t work. I could have swore I read further back that a 9 speed rear mech works with 10 speed cassettes so why couldn’t I use the 4700 series STI’s?

I repeat; for a 10s system to work with a 9s rear mech you need any 10s STIs other than 4700.



cheers

So the 105 5703 would be fine then?