Road bike triple chainring with Ultegra 6703 not shifting. Bike build part2

[Bice]

The bike



The chainring set-up



The problem 1



The problem 2



I am assembling this bike and I thought I had cracked it, as I wrote here: viewtopic.php?t=151640

But I haven't. Shifting onto the large chainring with the Shimano Ultegra 6703 front mech only works occasionally and only with huge strain on the gear cable.

Measuring the distance from the centre of the seat tube to the middle ring is, I reckon 47mm, not 45mm. (Even with Verniers I don't seem to be able to do this precisely.)

The result is that with a lot of pull on the cable (and the H limit screw almost out altogether) I occasionally get the chain on to the outer ring, but it is not happy. Sometimes the mech even jams there, which is alarming. The cable strain is excessive.

I bought the chainrings from Spa, which recommended a 113mm bottom bracket. (I bought one of the no-brand versions that they sell, but replaced it with a Shimano BB-UN55 113mm that I had as it was far smoother.)

I think that the problem is that the chainrings are sitting too far out from the frame, putting impossible strains on the cable and the mech.

I was thinking of trying a BB-UN55 110mm bottom bracket, but as you hopefully can see from the photos the space is small. The cranks might bottom out on the BB. But I think on the drive side there is 2-3mm to play with.

If that does not work, I was thinking of fitting an MTB / hybrid Alivio mech, which clamps from quite low down the seat tube. I have a similar set-up on my Carlton commuter road bike. It might even stay clear of this frame's braze on, which I would not need to grind off.

Very frustrating.

Even though this is a 48T, 38T, 28T triple chainring, the Ultegra 6703, designed for 50T, shifts pretty well.

[slowster]

Your chainset has a 10t difference between middle and outer chainrings. FD-6703 is specifically designed* for a 13t minimum difference. Because the inner plate of the derailleur cage is shaped with a channel to catch and pick up the chain from the middle ring, it does not work well if the mech is at the wrong height when it starts to contact against the chain on the middle ring. This is explained in this article by Jan Heine - https://www.renehersecycles.com/trouble ... i-triples/.

I think the solution in your case is to raise the front derailleur up to ~6mm higher than the normal position of 1mm-3mm above the outer ring (with the outer cage directly over the chainring). That should put the channel of the inner cage in the correct position when it pushes against the chain on the middle ring. 6mm might be higher than is optimal for your set up, so you might need to experiment a bit.

* https://si.shimano.com/pdfs/si/SI-5LX0B-001-ENG.pdf

[cycleruk]

You are right that the 6703 is designed for a 45mm chainline. (centre ring to frame downtube centre.)
The limiting factor in how far the chainset can be moved in (shorter BB axle) is the small ring catching the chainstay or even the crankarm catching as well. (wide chainstays as per MTB frame etc.)
One suggestion is to slightly angle the front of the derailleur out a couple of degrees. The idea being that the front of the FD will maybe move further out enough to push the chain over a fraction more than it would if fitted normally. Clutching at straws

[peetee]

In all probability the inner cage plate of the mech is contacting the middle ring and stopping the movement you require. Lift the mech a little, it still works fine. I have a 7800 groupset (the design of the mech is very similar) running 30-39-48 rings and the shift is fine with the mech a little high.
If I am barking up the wrong tree then perhaps it is that the cranks are too far out. Try a shorter length BB with, if necessary, a suitable thickness cassette freehub spacer ring behind the cup to fine tune the offset

[slowster]

I doubt that the chainline is a significant factor. I have a Spa triple with the same size outer and middle rings (48/38) and a 113mm UN55 bottom bracket, and it worked with the 105 version of the 10 speed triple front derailleur, FD-5703. The significant difference between the FD-5703 and the OP's FD-6703 mech, is that the FD-5703 is designed for an 11t minimum difference between middle and outer chainrings, and I did not find it necessary to significantly raise the derailleur to cope with the slightly under spec 10t difference.

[Valbrona]

Your chainset has a 10t difference between middle and outer chainrings. FD-6703 is specifically designed* for a 13t minimum difference. Because the inner plate of the derailleur cage is shaped with a channel to catch and pick up the chain from the middle ring, it does not work well if the mech is at the wrong height when it starts to contact against the chain on the middle ring. This is explained in this article by Jan Heine - https://www.renehersecycles.com/trouble ... i-triples/.

Spot-on.

[Bice]

In all probability the inner cage plate of the mech is contacting the middle ring and stopping the movement you require. Lift the mech a little, it still works fine. I have a 7800 groupset (the design of the mech is very similar) running 30-39-48 rings and the shift is fine with the mech a little high.
If I am barking up the wrong tree then perhaps it is that the cranks are too far out. Try a shorter length BB with, if necessary, a suitable thickness cassette freehub spacer ring behind the cup to find tune the offset

Thanks everyone for the above comments. All unaccountable error on my part. I had even read peetee's earlier post a few months back, echoed here by slowster and Valbrona.

I had actually set this front mech up correctly before putting the chain on. Only some weeks later did I complete the build, put on the chain and thought: why is the mech so high, and decided to lower it. Once the chain is on it is not so easy to see what the problem is, which is why I thought the bottom bracket was the problem.

This mech needs a 13T difference between outer and middle chain ring and I have 10T, as has been explained. To work I have set the mech quite a bit higher than ideal on the frame, but remarkably it does shift effectively.

I have only taken the bike around the block, and tomorrow I am going on a 70 miler, but I will use a different bike as I am with quite a no-nonsense group. This one's cables have been so weakened by clamping that I think it could break at any point.

I will test the bike properly when riding on my own.

The good news is that I really like the bike. It is coming in at 9.6kms, which is light for steel (and I have a steel seatpost here), and much lighter than I was expecting. But the main things are the huge tyre clearance and the bosses for mudguards and a rack. So its role is to be a fast light tourer.

[Bice]

Just an add: if the triple does not shift quite as well as I would like, I will dump it for a double: 48.34 and use that instead.

I like triples, but they are a hassle.

[Valbrona]

FWIW Shimano 105 FD5703 is compatible with your shifters and is able to cope with smaller diameter chainrings owing to greater curvature of cage. FD5703 requires min of 11t between middle and outer, as opposed to your FD which requires 13t.

I am successfully using FD5703 with 26/36/48. Tried 26/36/46 - does not work.

Happy tripling.

[peetee]

I like triples, but they are a hassle.

I would be interested to know why you think that.

[pwa]

I suspect the people who find triples a hassle do so, usually, because they are shifting with STIs. If you shift with a non-indexed bar end lever they are easy to use. It is the use of indexed STIs that is the problem. I remember having triple Ultegra 9 speed and having to give a bit of thought to each downshift. Big push or little push. It was such a relief when, after quite a few years, I rebuilt that bike with bar end levers and life became so much more relaxed.

But in this case, with down tube levers, the issue looks like a mech related one. I use a Sora mech on my 9 speed triple (non-indexed) because it was recommended as being better suited than dearer Shimano mechs, but I can't remember why. I think Chris Juden may have had something to say about it.

[Cugel]

I suspect the people who find triples a hassle do so, usually, because they are shifting with STIs. If you shift with a non-indexed bar end lever they are easy to use. It is the use of indexed STIs that is the problem. I remember having triple Ultegra 9 speed and having to give a bit of thought to each downshift. Big push or little push. It was such a relief when, after quite a few years, I rebuilt that bike with bar end levers and life became so much more relaxed.

But in this case, with down tube levers, the issue looks like a mech related one. I use a Sora mech on my 9 speed triple (non-indexed) because it was recommended as being better suited than dearer Shimano mechs, but I can't remember why. I think Chris Juden may have had something to say about it.

Three of the bikes in the bike shed have triples. Two of them have Shimano 30-39-52 chainsets and one a Spa 26-36-46 chainset.

One of the Shimano chainsets is a Dura Ace, working with an Ultegra triple front mech and an Ultegra LH triple shifter. Whilst setting these up requires proper adjustments, once they are set up they work perfectly, including the trimming clicks which are essential with such a system if one wants good changes without hesitation, chain-drop or any of the other front changing woes. The trimming clicks remove chain rub on the front mech that would be otherwise unavoidable in various ring-to-sprocket combinations.

The other Shimano triple chainset is an Ultegra, with an Ultegra triple front mech but a bar-end LH changer, as the brakes on that bike are hydraulic discs and I can't find a Shimano LH triple lever that does hydraulics. That system also changes without issue once set up; and a bar-end lever means trimming is easy albeit "by-hand".

The Spa triple chainset works with a 105 triple front changer set with the recommended 3mm gap above the big ring, using a LH bar-end changer. I do have a Shimano triple LH STI brake/gear lever but I currently use a bar-end triple LH lever because I'm keeping the triple LH STI one I have as a spare, in case t'other used with the Dura Ace setup fails. And I'm not sure the Spa chainset dimensions will work well with the Shimano LH triple STI lever, especially the trimming clicks.

***********
Triple chainset gearing systems are fiddly to set up but I find mine stays set up over the years, with only a bit of cable-tightening required at first, as the new cable stretches slightly.

Having fixed all sorts of little "it doesn't work" problems on the bikes of others, over the years, I suspect that many of these problems put the bike owners off such systems because the required fix goes beyond their tolerance for learning and applying the details of the fix. Many modern folk are used to the magic black box consumables that "just work" (or you throw them away and get a new one if they don't). I mean! Folk take their bike to the bike shop to get a puncture mended! Cuh!

Cugel, probably a gubbins fetishist.

[De Sisti]

problems put the bike owners off such systems because the required fix goes beyond their tolerance for learning and applying the details of the fix. Many modern folk are used to the magic black box consumables that "just work" (or you throw them away and get a new one if they don't).

I cannot disagree with the above.

I like triples, and as someone who isn't a qualified bike mechanic, I don't find them difficult
to set up. Using a mixture of Campag, Shimano and Spa components, I have the precise
combinations to suit my requirements. A shout-out must go to Mick Kelly (whom I used to
work with) who taught me some basic bike maintenance skills.

[Valbrona]

There isn't a contemporary/modern *road specific* FD that will shift the OPs 28/38/48. The last one to be capable of that would be 20 year old Campagnolo triple.

[peetee]

I’ve never found that triples are any more awkward to set up than doubles. The 30-39-48 on my road bike with a 11-25 cassette gives a perfect, comprehensive set of ratios with no nasty gaps. Sure, it weighs a bit more than a double but that isn’t noticeable in the slightest.