Cycling UK Forum

Is it the equivalent of mixing radial and cross-ply, or using WD as a chain lube?

'it depends'

Is it road compact? I have a 44/28 Spa Cycles super-compact chainset and a Deore LX triple mech. Upshifting was very difficult and most times the chain would fall off. LBS part-exchanged for a 105 double front mech and kept the same Deore LX shifters.

It’s a 48/34 Stronglight double.

Put the question another way, recommend me a suitable front shifter for a steel tubed touring bike. (I thought road shifters didn’t like to go below 50t outer.)

I'm sure a mech for 50/34 wouldn't have an issue shifting 48/34, unless the inner cage plate profiling is extremely specific!

Can be tricky finding mechs with a suitable clamp diameter for slimmer tubes these days, I find a lot more mechs with 31.8 and 34.9mm clamps than the 28.6 I need for my steel frames. Bigger clamps can be shimmed to fit but it can reduce the 'throw' of the mech towards the frame (i.e. the mech parallelogram binds before the cage hits the seat tube)which can be an issue depending on your chainline. I am using triples though.

What shifters are you using and what mech is it? The model numbers are needed as the shifting ratios have changed over the years.

The proposed mech is an FD-T8000 Deore XT. I’d running it bottom pull from downtube shifters.

The band is for a big fat 34.9mm - I don’t see how a shim affects the lateral positioning?

David9694 wrote:It’s a 48/34 Stronglight double.

Put the question another way, recommend me a suitable front shifter for a steel tubed touring bike. (I thought road shifters didn’t like to go below 50t outer.)

You mean 'front mech' here when you say 'shifter'..?

MTB mechs can vary from 'road' mechs (and from one another) in various different ways including

- mounting type (band on or braze on)
- mounting diameter (28.0, 28.6, 31.8, 34.9mm or other)
- maximum chainring size (range)
- recommended chainring interval
- cable pull direction
- recommended chainline
- recommended chainstay angle
- capacity
- permissible chainline range
- cable pull compatibility
- indexed cable pull compatibility
- cage width (5,6,7,8,9,10,11s etc)
- cage closure (screw, rivet or other)
- top swing or bottom swing
- size of mechanism (how much clearance it needs between the seat tube and the mudguard)
-position and type of mounting band
- whether or not the mech needs to have a cable housing stop built into it
- cable pull direction ( most front mechs are 'bottom normal' but some are sprung the other way and are 'top normal')

so there are lots of things which might trip you up or make things different/awkward for you. Before now I have suggested that when building a touring bike you should first decide what tyres you want to use; lots of things follow from that choice. A good second thing to choose on the whole bike is the front derailleur; lots of things follow on from that too.

There are many different Deore mechs; they have been making deore mechs since about 1982 or something so there are about twenty, maybe more in total. Most models that have ever been made can be had 'good used' or NOS from ebay and some of the older models might be a good match for an older touring bike; better than current models in fact (depending on the other things on the list above).

David9694 wrote:Is it the equivalent of mixing radial and cross-ply, or using WD as a chain lube?

actually that is a good analogy because neither of the two things above is unequivocally forbidden per se; there are situations where these things can be done. There are even occasions where they might be the best choice available.

cheers
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David9694 wrote:The proposed mech is an FD-T8000 Deore XT. I’d running it bottom pull from downtube shifters.

The band is for a big fat 34.9mm - I don’t see how a shim affects the lateral positioning?

If the chainline is not within the range permissible (and in fairness it will probably be OK with a double, but not a road triple necessarily) you can get a few mm of wiggle room by using an eccentric shim rather than the shim supplied with the mech.

How many speeds are you running at the rear? Also what size wheels are fitted to the bike?

cheers

Brucey raises some very good points.

Some time ago, I wanted to replace the drivetrain - including front derailleur - on my old Dyna-Tech MTrax600 MTB. The bike originally came with a 7 speed Shimano Exage ES groupset. I replaced this with a 9 speed set-up and tried to use a Deore MTB front mech (sorry, can't remember the exact model number). The 'throw' on this did not match my triple chainrings and after a bit of faffing about, I ended up swapping it out for an Alivio front mech which was fine.

As previous posters have commented, you may well be able to get the Deore mech working with no problems, but you you may also run into some problems. Aren't 'standards' just wonderful!

The cable routing is better on the T781, the T8000 routes the cable over a knuckle leaving a little bit of slack

Shimano 500LX will shift fine with STIs and smaller big chainrings and are in keeping with an older style narrow tubed bike, Shimano 6207 as well.

Brucey wrote:

David9694 wrote:The proposed mech is an FD-T8000 Deore XT. I’d running it bottom pull from downtube shifters.

The band is for a big fat 34.9mm - I don’t see how a shim affects the lateral positioning?

If the chainline is not within the range permissible (and in fairness it will probably be OK with a double, but not a road triple necessarily) you can get a few mm of wiggle room by using an eccentric shim rather than the shim supplied with the mech.

How many speeds are you running at the rear? Also what size wheels are fitted to the bike?

cheers

10s at the rear. Plan is to upgrade the existing Road cassette to a XT 11-34 and rear mech (please, God let that at least that part be simple!). 135mm OLN running a Deore hub.

700c with 38 gravel King tyres. Existing front mech is some ancient Shimano - works ok - space is tight with the fat tyre and it only just clears the chainstay.

A bit of background, this is my second resto from a few years back, an MB Dronfield frame with cantis which is evolving into an off-road capable bike. It had a stuck b/b, which I got out with the full vice treatment, but the threads were useless.

my guess is that the BB height is relatively low, the included chainstay angle is relatively small, and that you will probably get more clearance behind the seat tube with the 'high band' model. This means you should think of using a 'T' series FD (with 63-66 degrees compatibility), high band and you should check the specs carefully. So not any FD-T8000, but specifically FD-T8000-H3 (there are three other variants) as listed here

https://productinfo.shimano.com/#/spec/TREKKING/Front%20Derailleur

Remember that this FD is meant to work with 50mm chainline, meaning that is should work OK on the inner ring of a triple at about 42mm chainline. However a road double may be set to ~43mm chainline, which will mean that the chainline on the inner ring may be as little as 39mm (chainrings are centred ~8mm apart). This is different enough that the XT mech may not work at all; commonly this requires an eccentric shim to fix it on a frame with a 28.6mm seat tube.

cheers

I’ve installed the 11-34 XT cassette and XT rear mech, and all seems sweet. I’ll leave the front (FD TY15 GS) for now - just wanted to be Matchey-matchey, really.

But, being from the MTB stable, the cable pull on the new XT is putting the friction downtube shifter through nearly 180 degrees - is there any advice on improving this?