If I have

105 triple STIs (5703)
A 9spd XT rear mech
An Ultegra 10 SPD 12-30 cassette
A 46/36/24 triple chainset from Spa Cycles
A 9 or 10 SPD MTB front mech (whatever I have or can find)

Will it all work together, and do the biz nicely? I think it will, I just want to check.

Front mech may take some buggering around with but other than that should be fine.

Yeah, wondered about that, but then a roady triple front mech wouldn’t handle a granny ring that small, would it?

The MTB front mech is the only bit with a question mark hanging over, technically not compatible due to cable pull differences but can be made to shift*, depends how picky you are.

a roady triple front mech wouldn’t handle a granny ring that small,

Again, question marks… and a matter of exact models as cage profiles do change over time and between groupsets. Shimano tech docs are a mine of good info too! The issue is normally at the other end in terms of cage matching big ring radius, tiny granny rings are not so much of an issue, especially if you use a dog fang. The only become an issue when you couple them with a big outer ring meaning the cage isn’t deep enough for the chain not to rub on the bottom of it (when positioned high enough to clear the other rings).

For example I have an 8 speed Sora front mech that has been shifting a 48/38/24 triple on an audax bike for more miles than I can count and you’d be hard pushed to tell it wasn’t built to do just that it’s so reliable.

On the other hand I have a 9 speed Tiagra triple mech that just will not reliably shift a 48/36/26 triple on another bike no matter how hard I try, eventually put a 105 double mech on and bizarrely that’s better!

Have a look at the mechs meant for flat bar road/treking/touring chainsets as they are often meant for ~46-48t instead of 50-52T big rings (and consequently smaller middle/granny rings) and check compatibility with cable pull but you might find a decent match somewhere there.

*I won’t go as far as to say ‘work’

Good info, ta.

My 105 front mech and 5703 shifters runs a modded 105 triple (50/39/26) quite happily. I don’t know if it will cope with 50/39/24 but I might try my luck later this year (otherwise I’ll be paying Spa a visit for a different crankset). The back has a 9 spd Deore mech and a 10sp 11-34 cassette.

I use 5703 shifters with 9 speed xt shadow rear, 11-36 cassette. Up front is xt trekking chainset 48/36/26 and a 105 5703 triple roadie mech. Yours sounds workable, but the front mech needs to be just the right height or it won’t play.

pretty much run that except chainset is deore mtb touring 48 36 26 i think with an 11 34 out back using a long rear 9speed xt mech, front 9 speed XT

the front shifting isn’t perfect but works – takes a lot of setting up to get right – I use a wooden wedge to hold mech “open” to do cable tension and have an in line barrel adjuster – works best after cable stretch has disappeared so don’t be too unhappy if keeps needing adjusting with a new cable

Cheers chaps. I think I may actually be going for a 26 inner, and I have a selection of roady mechs, mtb mechs and barrel adjusters in the bits box, so I’m sure I’ll bodge something workable.

unless you’ve already got the cassette i was going to say go for a 26 inner and a 32 or 34 XT cassette

If you don’t need the big ring I did similar for touring last year but used a MTB cassette (11-36) and a 28/40 double, which plays perfectly happily with a road front mech.

I was using a tanpan to get a mtb mech playing with road shifters but only because that’s what I have.