Intermittent issue onto small chainring

[satanas]

^ Definitely not sacrilege - I used to do this all the time back in the day. A bit of creative bending of the cage plate(s) in various places and directions can solve quite a few shifting problems, improve clearance to the crankarm, etc. I usually used an 8"/200mm shifter to do this, but whatever works.

Probably not a good idea with Campag's carbon cage plates(!), and I'd be careful with alloy (like recent Dura-Ace), but steel is remarkably tolerant of being bent - carefully.

Later,
Stephen

[Brucey]

regarding chain compatibility with chainrings. Different chains shift differently for sure, hence trying a few different ones sometimes solves a problem. The other thing is that chains can run on a chainring but not truly be "compatible" with it..... eh?

I think what happens is that the chain needs a bit more clearance to the sides of the teeth than you might imagine in order to shift as easily as possible (*). IME the first shift to be affected is the middle to small chainring shift. It can drive you absolutely crackers trying to solve this kind of problem.

Anyway check the exact width of the chainring teeth and check for the kind of wear that leaves a burr on each tooth, which has the effect of making the tooth fractionally wider than normal.

(*) on the flip side this gives you a route to making a chainring that will work quite well on a 1x setup; take a 1/8" chainring, and file the teeth narrower so that it is (almost) a ram-jam fit on your chosen derailleur chain. The result is usually a chainring that works well on a (road) 1x setup, and doesn't unship the chain at all easily.

FWIW I think that tweaking FDs is pretty much fair game.

cheers

[fausto99]

Must admit I have not read more than the first page of this thread but I too am having intermittent problems with the very same low cost chainset from Spa. It is brand new, less than 500miles, with a new chain (on my winter bike with hub brakes as seen elsewhere on this forum) and it can be very reluctant to release the chain from the middle ring. I have changed the inner so that I now have 48/38/24, but it's the change up from the 38 to the 48 which sometimes is less than smooth. I can't see what's going on as I ride, but it feels like chain "suck". It's always perfect on the work stand of course. I'm hoping it will settle in with use but, having read some of Brucey's comments, I may try a different brand of chain, which is currently a KMC 8 speed.

[Sweep]

Another thought while I ponder spec sheets and think about buying new bits, including a new BB.

Yes I had certain issues before (beginning of thread) with a front mech nominally for 7/8 speed.

but at the mo things seem worse with the 9 speed front mech.

Could it be that that is part of the new problem?

The Chain Reaction page I linked to just upthread for the XT M771 says it is good for a 44 to 48 big ring.

and that fits what I have it on (48) though I do know from experience with chain reaction that their listings can be a bit odd.

BUT if I go to the Shimano tech docs they say:

To gear teeth 44 - I am using 48

Middle to top teeth difference 12 - my set up is 10, 38 to 48.

Could that be the new problem?

Re the supposedly required 12 difference that rather puzzles me as with my 10 difference the shift between top and middle both ways is absolutely fine.

Could the fact that I have it on a 10 difference between top and middle cause problems "further down" with the shift to the bottom? Would seem strange but just wondered.

The other odd thing is that I seem to remember that Spa recommended the Deore 591 front mech for this chainset, even though the 591 itself seems to be listed as for a 12 tooth difference.

113mm spindle BB going on order with the good folks at Rose tomorrow.

[NetworkMan]

The other odd thing is that I seem to remember that Spa recommended the Deore 591 front mech for this chainset, even though the 591 itself seems to be listed as for a 12 tooth difference.

I don't think they'd advise a Deore FD for the XD2 chainset. It has a chainline of ~45mm so needs a road derailleur not an MTB one. Spa use a 9 speed Sora road FD on their tourer with an XD2. I have an XD2 with 48/38/24 on my tourer and use a Claris 8 speed. On my Spa Audax I have the similar TD2 48/38/28 and use a 9 speed Sora on that. BTW the Q-factor is not directly relevant to shifting performance; it's just a measure of the distance between the pedals.

Excuse me if it was discussed upthread but I couldn't see any mention of adjusting the lower limit screw. If you loosen this (Shimano suggest 1/4 turn in my data sheet) it allows the FD to shift over further in the direction of the small ring, assuming the cable is slack which it should be. Of course if you go too far there is a danger of the chain falling off the small ring.

To maximise your chances of success I think you should be using a 9 speed road FD intended for chainrings close to 48/38/28. The Sora is intended for 50/39/30 which is pretty close, and the size of the little ring is not very important. I don't think a mountain bike derailleur is appropriate for this chainset when used with the recommended 110 mm BB; it is intended for a chainset with rings further out from the frame. I'm not sure if you need top or bottom pull and you'll need a road compatible shifter of course. I can't help here since I don't know anything about flat bar shifters, except to say that Shimano used to make suitable ones for so-called fitness bikes.

[satanas]

If shifting onto the small ring of a triple is reluctant, one possible solution is to use a Deda Dog Fang (or similar) to prevent overshifting onto the BB shell, and then to undo the inner limit screw as far as is necessary, i.e., until the shift happens reliably.

Also, the closer the outer cage plate is to the middle ring, the better the downshift ought to be, so it's best to avoid FDs intended for bigger middle-to-outer gaps than you will be using; these must be mounted higher.

Some combinations seem to shift abysmally for no obvious reason, and I'm inclined to think that misaligned pins and ramps often make shifting worse, not better, unlike matched sets.

Best of luck

[Sweep]

Many thanks for that network man.

Am thinking of fitting one of my stock of Altus shifters:

this:

https://www.rosebikes.com/shimano-altus ... e=standard

chain line of 47.5 to 50 it says.

and fitting a 113 spindle BB.

Might work?

Am pretty sure Spa recommended that Deore, even though I was doubtful.

Can't remember if this was a recco in a phone conversation or by mail.

Perhaps they were having an off day.

[Sweep]

Many thanks for that network man.

Am thinking of fitting one of my stock of Altus shifters:

this:

https://www.rosebikes.com/shimano-altus ... e=standard

chain line of 47.5 to 50 it says.

and fitting a 113 spindle BB.

Might work?

Am pretty sure Spa recommended that Deore, even though I was doubtful.

Can't remember if this was a recco in a phone conversation or by mail.

Perhaps they were having an off day.

>>I'm not sure if you need top or bottom pull and you'll need a road compatible shifter of course. I can't help here since I don't know anything about flat bar shifters,

On this, this has long puzzled me. What is this compatibility issue? The front mech has no clicks itself but surely just pulls to where the shifter takes it? And then stops? Are the chainrings on road and MTB chainsets spaced differently? Sorry, probably being really daft and missed something obvious.

I did have an older Altus on there before, in fact the original the bike came with, and that was supplied, though I didn't ride the bike at that time, with a 48/38/28 chainset and that worked better, if not perfectly, than the XT.

Maybe because of its advertised 47.5 to 50 chainline and its advised middle-top gap of 10.

[CREPELLO]

Has the eccentric shim for the FD been mentioned yet? Assuming that the XT mech is a 34.9 tube fitting and your frame tubing is 28.6mm, the shim below will work well in moving the mech inwards further - achieving that reliable shifting you are after. It also has the benefit of being able to move the FD for and aft a bit, which can be useful.

https://www.sjscycles.co.uk/gear-spares ... hed-split/

[Sweep]

Has the eccentric shim for the FD been mentioned yet? Assuming that the XT mech is a 34.9 tube fitting and your frame tubing is 28.6mm, the shim below will work well in moving the mech inwards further - achieving that reliable shifting you are after. It also has the benefit of being able to move the FD for and aft a bit, which can be useful.

https://www.sjscycles.co.uk/gear-spares ... hed-split/

thanks for that. And I see that the second appreciative review mentions precisely my problem.

Will consider if all else fails as this is a favourite bike.

And I also have a twin frame - though that will be built with a top ring of 44.

by the by, I have discovered that the chain on it is an SRAM after all, so as per Brucey's suggestion I will probably try putting one of my KMC chains on it.

The other thing I will try is judiciously bending the Altus mech if it doesn't at first work. Quite happy to experiment with something so cheap. And in any case it appears as if the XT front mech is unsuitable - no loss - can be stored as a spare for one of my other bikes.

Oh, good call of yours (or supernatural powers?) in judging the seatube diameter I am putting the mech on to and that it is shimmed.

My original Altus wasn't shimmed but the new one I will try on the bike will be.

[NetworkMan]

On this, this has long puzzled me. What is this compatibility issue? The front mech has no clicks itself but surely just pulls to where the shifter takes it? And then stops? Are the chainrings on road and MTB chainsets spaced differently? Sorry, probably being really daft and missed something obvious.

My information is rather old but traditionally the mountain bike FDs have needed about 45% more cable pull than the road ones. I don't know if things have changed recently but don't see why they should have. The MTB FD has a stronger spring and so has an effectively longer lever arm to compensate. This in turn means that the shifter has to pull more cable to achieve the same motion at the FD cage. I've read that a road STI won't work well with an MTB FD but I don't actually know what happens with a flat bar MTB shifter when it's required to pull less cable than designed. AFAIK the chainring spacing is no different; that's more likely to depend on the number of speeds and hence the chain width.

If you go from 110 to 113 mm you'l only be moving the chainrings out by 1.5 mm so the chainline will go from 45 to 46.5 mm., assuming that the BBs are as claimed which may not always be true with tolerances etc so if you are going down that route you should probably use a 115 mm BB so as to get the chainline up to the MTB 47.5 mm nominal.

Did you try fiddling with the low limit screw on the FD - and noting the point upthread about fitting a jump stop to prevent the chain from falling off the little ring onto the BB shell?

[Sweep]

Did you try fiddling with the low limit screw on the FD - and noting the point upthread about fitting a jump stop to prevent the chain from falling off the little ring onto the BB shell?

The mech seems to have gone in as far as it will go. Have pulled the limit screw out a long way. I can't actually manage to get the chain to fall off the bottom Just getting it on to that bottom ring is, as I said, hit and miss - sometimes struggles/refuses, sometimes drops sweetly. When on the stand and using my hands to release the cable from top to bottom drops on particularly sweetly.

Which puzzles me.

Thanks for your patient replies.

[NetworkMan]

Did you try fiddling with the low limit screw on the FD - and noting the point upthread about fitting a jump stop to prevent the chain from falling off the little ring onto the BB shell?

The mech seems to have gone in as far as it will go. Have pulled the limit screw out a long way. I can't actually manage to get the chain to fall off the bottom Just getting it on to that bottom ring is, as I said, hit and miss - sometimes struggles/refuses, sometimes drops sweetly. When on the stand and using my hands to release the cable from top to bottom drops on particularly sweetly.

Which puzzles me.

Thanks for your patient replies.

Ah, I see. That's consistent with the MTB type FD being unsuitable for the 45 mm chainline of the Spa road chainset - the FD is too far out from the frame or conversely the chainrings are too far in. When you are on big sprocket and little chainring (lowest gear) is the chain rubbing on the near side of the FD cage? I'm trying to estimate just how far you need to move the FD and/or the rings.

BTW the change from middle to little can be easier if done from a higher gear on the rear rather than a lower. That's because the cage is closer to the chain under these conditions and so it's easier to get the chain to derail.

[CREPELLO]

Sweep, this maybe what you need https://www.ebay.co.uk/itm/SHIMANO-FD-R ... :rk:7:pf:0

Although it's designed for a 12T difference, middle to big ring IIRC and a 50T big ring, it's pretty close to your set up. In it's favour it's a 9 speed cage and made for a road chainline. Bonus - it's all silver

[MikeF]

Did you try fiddling with the low limit screw on the FD - and noting the point upthread about fitting a jump stop to prevent the chain from falling off the little ring onto the BB shell?

The mech seems to have gone in as far as it will go. Have pulled the limit screw out a long way. I can't actually manage to get the chain to fall off the bottom Just getting it on to that bottom ring is, as I said, hit and miss - sometimes struggles/refuses, sometimes drops sweetly. When on the stand and using my hands to release the cable from top to bottom drops on particularly sweetly.

Which puzzles me.

Thanks for your patient replies.

I've read this thread with interest as I have similar issues on 1 bike. Dropping from big chain ring to small works very well even when the chain is under tension, but middle to small isn't so good; the middle ring seems to want to "hang on" to the chain. However on the road you might find the chain can drop off the inner ring when it's thrown from the large ring. I've fitted a jump stop to stop this happening. As others have said, changing down when the chain is on one of the smaller rear sprockets might help.
You may find the slightly longer BB is all you need.