3

I bought a new bike specced with a sora front derailleur and left brifter. I've been unable to make the front derailleur shift properly. I sent a message to the manufacturer (no response yet) but I suspect this might be more technical than their customer support is used to.

Right now, the core problem seems to be that the front derailleur cannot swing far out enough to stop rubbing the outboard side of the chain when on the large chainring. I don't see anything blocking the derailleur from traveling further, but when attempting to push it further by either tugging on the cable or manually rotating the cage, it does not budge.

Top down picture of the cranks:

Top down picture

Derailleur cage does not go past this point:

Frontal image

Neither limit screw is making contact.

Image of limit screws

I have checked the alignment by setting the top edge of the outer cage parallel to the chainring.

I suspect that the bike is specced with a chainline too far for the derailleur. I measured (with a little difficulty):

Inner chainring (center of tooth) is ~44mm from center of seatpost.

Outer chainring (center of tooth) is 51-52mm from center of seatpost.

How can I make this work? I think I could potentially gain 3mm by moving that bottom bracket spacer to the other side, but I don't think it would be enough.

7
  • Generally: it's a lot easier to use the visual method in the Dealer's Manual (si.shimano.com/en/pdfs/dm/RBFD001/DM-RBFD001-01-ENG.pdf) than to follow Calvin Jones's audible method (youtu.be/ZNG7g83lI-s). Specifically for your problem, just as a first guess: can you add tension to the cable using the barrel adjuster (to close the gap to the Hi bolt)?
    – Sam7919
    Commented Nov 8, 2023 at 3:15
  • @Sam7919: He said he can’t move it outwards even when he pulls directly on the cage and the limit screws don’t make contact.
    – Michael
    Commented Nov 8, 2023 at 6:27
  • I don’t know how a Sora front derailleur is supposed to look, but the part which touches the chain almost looks bent? Maybe damaged during shipping? It also looks quite narrow. On my Ultegra R8000 front derailleur it’s almost twice the chain width. But maybe it’s just the angle …
    – Michael
    Commented Nov 8, 2023 at 6:31
  • Is it straight? Looks like a clamp-on mechanism and in picture #2, only the front edge touches the chain while there is plenty of space on the back?
    – DoNuT
    Commented Nov 8, 2023 at 6:43
  • 1
    @DoNuT The top outer edge of the cage is parallel to the chainring. The bottom edge is not a straight line, it has that curve/protrusion at the front that goes inward towards the chain.
    – Edward
    Commented Nov 8, 2023 at 14:02

3 Answers 3

3

It seems like a similar issue is occurring with your bike. I own a JAMIS gravel bike, the Renegade S4, equipped with a SORA front derailleur, shifter, and an FSA crankset with a measured chainline of 48mm.

Despite my extensive experience in bike assembly and adjustments, I faced similar challenges. The root cause is the deviation between the recommended 43.5mm chainline by SORA and the actual measurement of 48mm on our bikes. This discrepancy might be intentional, considering budget constraints.

Gravel bikes, designed for wider tires, often have chainstays that bulge outward, requiring a smaller gear or a longer chainline to avoid interference. However, in the budget-constrained realm of complete bikes, dedicated gravel components like GRX or RIVAL are not always available. While SORA is cost-effective, its compatibility with larger gear sizes necessitates pushing the chainline outward, causing the problems we're encountering.

One solution is to switch to a front derailleur designed for gravel bikes (such as GRX, RIVAL, Microshift SWORD). However, attention must be paid to the chainring size, as some products may not accommodate excessively large chainrings.

Another approach involves removing the bottom bracket or spacers to reduce the chainline, but caution is required to avoid interference with the frame.

As a last, budget-friendly option, adjusting the front derailleur's tail inward is possible. However, this may not guarantee a resolution, and even if successful, it may not provide optimal shifting.

2
  • Thanks for the answer. I considered the possibility of a different front derailleur, but I can't find a suitable one- 9 speed, clamp-on, 48-49mm chainline, and compatible with sora shifters. The ones that I can find are 10+ speed and only 45-46mm chainline. Do you know of a match?
    – Edward
    Commented Nov 22, 2023 at 23:27
  • In the mean time, I've been able to modify this derailleur to cleanly reach the large chainring- at the expense of massive chain rub in the small chainring.
    – Edward
    Commented Nov 22, 2023 at 23:28
6

The problem is the presence of the spacer underneath the drive side BB cup:

enter image description here

This appears to be a Shimano road crank, likely the matching Sora FC-R3000, in a Shimano road bottom bracket, likely BB-RS501 (but it could be any of them since they interchange). Shimano threaded road Hollowtech II BBs never are supposed to have a spacer under either cup, as you can see in their EV diagram. Its presence will force the front chainline further out than intended, which in turn will make the FD need to be adjusted quite a bit further out than intended, and as you've discovered this model doesn't have much wiggle room in this regard.

It's very important to note that putting spacers under the cups of Shimano road BBs has a more serious danger: it takes away from the intended engagement of the crank spindle splines into the non-drive crank. The BB will still adjust normally but the crank won't be hanging onto the spindle with as much surface contact as designed. This can be very dangerous and also can ruin the crank.

If the bike is still new and never/lightly ridden, you're likely fine to just remove the spacer and re-adjust everything, which of course is an unfortunate thing to need to do on a new bike. What's really in question here is how whoever was building it up the first time got to the conclusion of adding it there. If the answer is otherwise there's some kind of crank or chainring clearance problem with the frame, it would be best to wash your hands of this bike and return it, because that's basically a defect in design or manufacture and there's not really a good hack or workaround to solve it and make everything else work as intended, nor should you be on the hook for dealing with it.

Edit: Per the comments, the above makes incorrect assumptions about what the crank is, but measuring the BB bearing face-to-face dimension as 92 does tell the story here. 92mm is what a mountain crank would use and the face-to-face dimension that their bottom brackets would give (for example, it's the same 92 as in BB92, the press-fit BB standard for mountain bikes). These cranks are likely simply wrong for the front derailleur and are putting the rings too far out and there's no way the FD can reach. This is consistent with measuring the chainline at around 47.5mm-48mm (the halfway point between the two individual chainline measurements in the question). That number would be normal to see on an older mountain or hybrid double, but is quite a bit more than the 43.5mm listed as the chainline spec for FD-R3000. Switching the spacer to under the left cup may be able to make it go. If it weren't, there could be routes that use a different front derailleur combined with a braze-on adapter that spaces the FD out more.

5
  • The crank is not shimano but "Neco"- I got this bike cheaply enough ($260 shipped) that I am set on making it work, even if it requires replacing a new part or two.
    – Edward
    Commented Nov 8, 2023 at 18:34
  • 1
    In that case it's likely that if there is a solution with the parts you've got, it involves taking away the spacer or switching what side it's on. Be careful that the crank spindle engagement into the left crank looks right. Another good test to do would be measure the face-to-face dimension of the BB, the dimension that the cranks "see." If it's some other number than 86.5mm or close, that still likely indicates the presence of a spacer that shouldn't be there, since that's the number that basically all external road/gravel cranks are aiming for. Commented Nov 8, 2023 at 18:40
  • I measured 92mm...
    – Edward
    Commented Nov 9, 2023 at 1:08
  • @Edward Edited, looks like I got it wrong the first time around. Commented Nov 9, 2023 at 1:43
  • However, with putting all spacers on the left, the position of the pedals could be awkwsrd. It will be less of an issue with flst pedals but still could give you a tendency tu put your legs in strange angles. OTOH I use a longer pedal spindle on one side intentionally due to my duck foot on one side (and non-straight legs in general). Commented Nov 24, 2023 at 7:24
1

Since I can't reply in the comments section, I'll provide a new response.

Officially supporting a chainline of 48mm to 49mm is primarily the domain of MTB derailleurs. However, MTB derailleurs usually do not accommodate larger chainring sizes (like a road bikes). While this replace might eliminate chainring rubbing issues, it could result in severe upshifting problems.

GRX400 supports a 46mm chainline, and Microshift SWORD accommodates a 47mm chainline officially. Although they don't reach 48mm, they can move outward by 2.5 to 3.5 mm beyond SORA, potentially improving the situation. Additionally, while officially designed for 10-speed, based on my past experiences, it should function without issues. Shimano's compatibility list is still too strict.

However, there's no guarantee that solutions will work.

If it were me, I would start by switching the derailleur to GRX. Furthermore, if there is no interference with the frame after removing the BB spacer, remove it. And see how it performs. It's a relatively simple and comparatively inexpensive change.

If that still doesn't address the issue, consider swapping the crankset to one with an appropriate chainring that matches the frame, aligning it with the timing of a bottom bracket replacement. This way, you can ensure compatibility with the frame and achieve the desired chainline.

1
  • 1
    Good first answer! Just for info, there are a few MTB derailleurs that support 46/30 chainrings. 2 in 9-speed: Microshift Advent and Shimano FD-T3000-2. In 11-speed, there are also a bunch of front derailleurs in the Shimano CUES range. The options are very limited, but they exist.
    – Rеnаud
    Commented Nov 23, 2023 at 14:21

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.