Which Front Mech?

For discussions about bikes and equipment.
Timuk
Posts: 19
Joined: 17 Feb 2015, 5:04pm

Which Front Mech?

Postby Timuk » 29 Jul 2015, 10:13am

Hi recently changed the drive train on my Salsa Vaya and now have 105 triple shifters (original)with an XT x780 triple chainset (42-32-24).

At the back is now a xt 771 9 speed mech and 11-36 xt cassette with a new 10 speed chain.
I can now pedal up a virtual wall :-)

Everything is working well at the back but I have run into a slight problem - it works at the front but the changing is not quite as smooth I would like

I moved with the 105 front mech down the seat tube (as the chainrings are so much smaller than the original 105) but cant really get it as low as I would like as the mech would foul the chainstay if it was adjusted to 2mm above the largest ring (being quite long)

A new xt front mech is only £15-£20 discounted so I will get one, but am not sure which variant will work best or at all

Will the 771 be suitable?
http://www.wiggle.co.uk/shimano-xt-m771 ... erailleur/

or the 781 ten speed work
http://www.wiggle.co.uk/shimano-xt-m781 ... erailleur/

There is also
http://www.wiggle.co.uk/shimano-xt-m770 ... erailleur/
Which is available as a BB mount - which I guess would mean that height positioning is even easier?

Not sure if pull ratio compatablilty etc is important with indexed front mechs as it is with the rear mechs
Anyone can point me in the right direction for 105 front shifters - 10 speed triple and which xt front mech :-)

Many thanks

Brucey
Posts: 36821
Joined: 4 Jan 2012, 6:25pm

Re: Which Front Mech?

Postby Brucey » 29 Jul 2015, 10:36am

'which XT mech?' -without modification, none; they all require too much cable pull for your shifter.

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

Timuk
Posts: 19
Joined: 17 Feb 2015, 5:04pm

Re: Which Front Mech?

Postby Timuk » 29 Jul 2015, 10:43am

Ahhh - right

Any idea if there is a smaller front mech that will be compatible with 105 shifters? (i.e. more suited to smaller diameter chainrings)

Brucey
Posts: 36821
Joined: 4 Jan 2012, 6:25pm

Re: Which Front Mech?

Postby Brucey » 29 Jul 2015, 11:56am

with this shifter there are two broad types of solution;

1) finding a mech with the right cable pull that will work with those chainrings, by accident or design, or

2) finding ways of using an MTB mech so that the cable pull differences are resolved.

The latter can involve using a different cable mount on the mech or perhaps a shiftmate.

In general terms this kind of setup can be a right PITA to sort out because even if you find a 'road' mech that works OK on those rings and doesn't clash, there is not guarantee that it will either;

a) reach out far enough for an MTB chainline or
b) have the right shift ratio even if it reached out far enough; the shift ratio varies through the stroke.

All of which explains why it is that indexed front shifting is widely regarded as a daft idea once you stray away from manufacturer-recommended combinations. For some years I have an ultegra 9s setup, with triple-compatible shifters driving a double mech/chainrings, all Ultegra. The shifting was never quite right because of a type b) problem, I think.

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

pickerd1
Posts: 36
Joined: 31 Mar 2014, 5:05pm

Re: Which Front Mech?

Postby pickerd1 » 29 Jul 2015, 12:55pm

Hi,
On my Salsa Vaya I have ....
- Rear 10 speed cassette - Tiagra 12-30 (customized sprockets) with 105 med cage RM. I did have a 9 spd MTB long cage mech, RD-M591, but this did not shift quite as well. The advantage of this long cage was that I could easily use all ring / sprocket combinations, with the 105 med cage this is restricted a little but I never use big - big or small - small combos.
- Front - modified Deore M610 with 24 / 36 / 46 rings - with Tiagra triple FM
- KMC chain
These work quite well with 105 shifters. The rear shift is now perfect after a settling in period. The front shift from inner to middle ring is not always perfect. I have to move the lever again (not full click) to give the FM an extra bit of movement. This depends on which rear sprocket I am in - all to do with chain position relative to the FM I suppose.

I plan to try the following on my Croix de Fer ...
- Rear 10 speed cassette - Ultegra 12-23 with 105 short cage RM
- Front - modified Deore M610 with 22 / 32 / 42 rings - with Tiagra triple FM
- KMC chain
- Tiagra 10spd / triple shifters

So far this looks ok - the FM is 2mm from the big ring and does not foul the chain stay at the bottom of it's travel.

I will post shifting results later when I fit the chain.

Dave

Norman H
Posts: 883
Joined: 31 Jul 2011, 4:39pm

Re: Which Front Mech?

Postby Norman H » 29 Jul 2015, 1:50pm

A PITA as Brucey says.

Presumably the original chainset was a road triple. If you were trying to achieve a lower bail out granny gear you could have gone to 24T inner using a conventional 130/74 BCD or 110/74 BCD road chainset.

If I've understood you correctly, you are currently running a mtb chainset with a road front changer. Generally road mechs work best with a road chainline and mtb mechs work best with a mtb chainline. In addition, current Shimano front road mechs are happiest with a minimum difference between middle and outer of around 12T. With only a 10T difference and setting up with the recommended 2mm clearance, you risk the inner cage hitting the middle ring. Older road triples with less deep inner cages are better in this respect. Also as you have discovered If you lower the front mech too much it will hit the chainstay. I suspect your shifting issues may be as much to do with chainline as with ring sizes. Sometimes chainline issues can be resolved using an oversized clamp on mech and an eccentric shim.

I believe Spa do square taper 104 BCD chainsets which would also allow you to fine tune the chainline.

Timuk
Posts: 19
Joined: 17 Feb 2015, 5:04pm

Re: Which Front Mech? - sorted now ty

Postby Timuk » 29 Jul 2015, 5:02pm

Made some further adjustments to the mech positioning and the lower stop and all is now working fine!

The rear is silent and snicks nicely up and down and the the front is at least as good as it was with the 105 chainring/cranks - as has been said indexing a front mech does seem a little unnecessary.

Just been out for 30 miles up and over the Howardian Hills with a panniers full of Shopping and the overall gearing seems much better for me.

42 front :11 rear seems to be about 24/25 mph - more than I can maintain unloaded - so this is ample for a tourer imho.

The gear range overall I have now really suits me and the cycling I do gives me a really useful range of gears whilst still having the clean cockpit of 105 integrated shifters

Anyway thanks for the helpful replies

Cheers

scottg
Posts: 705
Joined: 10 Jan 2008, 8:44pm
Location: Highland Heights Kentucky,, USA

Re: Which Front Mech?

Postby scottg » 29 Jul 2015, 6:15pm

One rider uses a cheap Falcon friction thumb shifter with a XT from mech,
in a setup similar to yours. His STI left shifter had broken, it is used only as brake lever now.
You could also use a bar con shifter.

This works down to 46t, haven't tried with smaller rings.
http://store.interlocracing.com/alfrde.html
+++++++++++++++++++++++++++++++++++++
Why not the best, buy Cyclo-Benelux.