Front derailleur recommendation?

[MikeMc]

I'm having trouble finding a suitable front derailleur for my TA Zephyr (48/36/24) and Dura Ace bar-end shifter. I had a Sachs and a Sun X-1 to try but both seem to require more cable pull than the shifters can give. As a temporary measure I've run the cable on the inside of the bolt on the Sachs front mech but would prefer not to bodge it. Will a low end Shimano Sora be enough?

Any recommendations gratefully received.

ps. The rear shifter works fine on a XT rear mech and 9sp 11-32 block.

 

[TheDoctor]

A Sora will shift a 48/36/24, I'd have thought. I had a Sora triple (8 speed) shifting across a 48/38/24 with STIs, so I'd be astounded if it didn't do 48/36/24 with a bar-end.

 

[RecordAceFromNew]

Shimano's spec says the 8 speed triple front mech's capacity is 22T, so there is a chance that it won't, but not a huge chance. However I would definitely check the chainline to ensure it is around 45mm. If not you might be better off with a mountain mech.

 

[PpPete]

More of a problem on mech height and/or chain line than with the mech itself IMHO
One of our family stable runs a Sun X-1 mech quite happily on a 48/38/26 Impact Triple....
The drop down to 24T is not going to require more cable pull.

That said I've run both Tiagra and 105 FDs on a 50/38/26 triple which is, as RAFN points out, is beyond Shimano's 22T maximum difference between big ring & granny (same range on all Shimano's road FD's IIRC)

 

[Tim Bennet.]

I run 26/40/50 on all the bikes and use either Ultegra, Centaur or some 30 year old Suntour thing.
There always seems to be plenty of pull on bar end shifters.

 

[RecordAceFromNew]

Strictly speaking I think cable pull will not be the issue for the OP, since I would have thought the distance between his chain rings must be within the usual norm.

Chainline could be an issue if he breaches the design spec, and if his front mech is unable to over or under reach to compensate for any error there due to the mech's mechanical limits or clash with the frame.

The potential problem of using a front mech beyond its tooth range, however, is that after the OP sets his mech to have a 2mm clearance from the big ring, he might find that the chain hits the mech's tail when it is on the small ring. It is hard to tell whether this will happen because it is dependent on his seat tube angle (the more vertical the worse) and bottom bracket height in relation to the rear wheel axe (the higher the worse). Apparently for the occasional frame a front mech won't even work within "official" spec.

It is probably noteworthy, that afaik Shimano's mtb front mechs don't have higher stated maximum capacity than their road mechs (i.e. 22T). However since mountain bb's are generally designed to have higher ground clearance while rear axles are lower compared to road's, the OP's chance of being able to exceed a mountain mech's capacity is probably better, as long as he doesn't hit problems mentioned above in relation to breaching a mech's chainline spec.

 

[MikeMc]

Thanks for all the advice.

The chainline is just over 47mm and but to bring it in will require a new BB and possibly spacers to bring back it out again. How close can the inner ring be to the middle i.e. I'm thinking of changing the spacing. What should it ideally be for a 9 speed?

I'll start with trying an XT front mech. It looks like I'll end up with more parts than I started with.

 

[RecordAceFromNew]

According to Shimano's front mech compatibility chart, depending on your bike's configuration (see top right of chart), it seems the Deore [url="http://techdocs.shimano.com/media/techdocs/content/cycle/SI/Deore/FrontDriveSystem/SI-F740I-En_v1_m56577569830612824.pdf"]FD-M510-6 or FD511-6[/url] are probably your best bet. They are designed for your current chainline, while being mountain mechs hopefully would offer you more tooth capacity leeway than otherwise.

But if you have an XT already, it would be worth trying it. The chance that it works is not zero albeit it is designed for a 50mm chainline.

Could you explain why you want to fettle with the chainline/bb at this point? Is it because you have a Sora triple front mech already? If so does it not work and if that is the case which problem (given it is officially neither right for chainline nor capacity) are you encountering?

Regarding speed imho whether the front mech is for 8 or 9 speed is immaterial. The relevant issue there is 50% of the respective width of such chains, and the difference is tiny (about 0.25mm).

 

[MikeMc]

The chainset is new on this bike and required a new BB as the inner chainring bolts rubbed on the frame. I had not realised that a few mills would make such a difference.

 

[RecordAceFromNew]

Matching bb to chainset, when they are from different manufacturers, and when there is no spec sheet for guidance, can indeed be a little tricky. I don't think this is going to help you very much at present but you might want to take a look. If your bb is Shimano, then you would need to take extra care in selection since their bb's follow the JIS standard while TA is ISO.

If you have a front mech already and the chainset is rubbing, and the bb is square tapered you can always use the kitchen tin foil trick to check out the function of the drivetrain at different chainlines with your existing bb and front mech(s) before selecting and buying the right bb.

 

[MikeMc]

Thanks for that info. That would explain why on the previous Shimano 122.5mm BB the bolts touched the frame. Peter White cycles mentions a BB length of 127 for a 45mm chainline.

Do you know if Royce tapers are ISO as I have a 126mm ti BB that I could use?

 

[RecordAceFromNew]

Thanks for that info. That would explain why on the previous Shimano 122.5mm BB the bolts touched the frame. Peter White cycles mentions a BB length of 127 for a 45mm chainline.

Do you know if Royce tapers are ISO as I have a 126mm ti BB that I could use?

Impossible to tell re Royce, afaik they do both.

You might be interested to know that ISO tapers are smaller than JIS's, so an ISO crank should sit further out on a JIS bb. According to the late great Sheldon it is around 4.5mm (although imho this figure, in the wild world of square tapers by different manufacturers from different vintage, may not be reliable).

I don't know if the above contradicts Peter White's note about the specific TA bb of 125mm. However in any case that bb is asymmetric (6mm longer on the right, since he said the 131mm one delivers same chainline but symmetric cranks), Shimano's bb's are also often asymmetric, but likely by different amounts (e.g. less in the present case). It is therefore unreliable to compare them by spindle length, it could be like comparing apples and oranges.

You might want to know, however, that replacing a 122.5mm Shimano square tapered bb by a 127.5mm one adds 3mm to the chainline.

Front mech compatibility consideration is a doddle in comparison huh? Hope the above helps a bit.

 

[MikeMc]

I mentioned that the Dura Ace shifters were not pulling enough cable. It seems this happens if they are not installed properly. Who knew! I had inserted part 2 on the left lever rotated by 180 degrees. The result was that the levers only moved through 90 instead of 150 degrees.

Onwards and downwards.

 

[canamrider]

I mentioned that the Dura Ace shifters were not pulling enough cable. It seems this happens if they are not installed properly. Who knew! I had inserted part 2 on the left lever rotated by 180 degrees. The result was that the levers only moved through 90 instead of 150 degrees.

Onwards and downwards.

I've done this a couple of times myself and suffered severe irritation when something that worked so well before disassembly won't work correctly after being put back together.