[roadbikepilgrim]

Good afternoon,

One here for the home mechanics and any Shimano pro mechanics who are on the forum. About a  year ago I managed to get a Claris triple groupset at a bargain price, so I swapped out the Microshift R8 triple groupset that came with my Triban 500 SE bike.

Installation was fine and the Shimano groupset overall is better than the Microshift was. Only one problem. I could never remove front mech rub when in the large 50T chain ring and the smallest 11T sprocket on the cassette. Dialling out the limit stop (to the point where the chain should really have been falling off the large ring) and increasing the cable tension (beyond the point of overdoing it) would not help put space between the chain and the front mech outer plate. I was following Shimano’s instructions in their dealer manual to the letter and it was just no joy. Besides, the setup of the Claris triple front mech is really boilerplate for a front mech, with no special setup features that you need to be aware of. In the end I shrugged my shoulders, created a bit of mech rub in the small chain ring large rear cog combination (in order to throw the front mech cage fractionally further out and give more space between chain and front mech outer plate) and resigned myself to some noise at both ends of the gear range.

However, yesterday I was putting on a new cassette and chain and while I was checking that indexing was still okay, I had the idea to pull on the front mech cable (externally cabled frame) while the chain was in the small rear large front combination. Suddenly the rubbing was gone and the front mech did what you would expect: it went out as far as the limit screw setting. When just using the shifter it matters not where the limit screw is set: the cage will just not go out far enough to avoid rubbing. So, I realised that the problem was not the front mech (the spring, the limit screw setting or the cable tension), but it was actually the shifter that was limiting the movement to allow sufficient cage clearance in the small rear large front combination.

Does this sound like a manufacturing fault with the shifter (its range is just slightly too short for three chain rings)? Is there an adjustment that can be made to the shifter’s mechanism (saw nothing about this in Shimano’s manual)? Or is that just the way that the Claris triple shifter functions, and the front mech rub is a “feature” and not a bug for the lower end groupsets?

All views welcome. It’s only my commuter bike, so I can live with the mech rub. But my pride wants to solve it!

Thanks and regards,

roadbikepilgrim

Topic

[roadbikepilgrim]

Hi Gus,

Hi Gus,

Thanks for your further response. I have been thinking about this more, and while the reduction in BB length might have at first sounded like a solution, I am not sure it will be.

I have had a really close look at the BB shell on my bike and how the current BB is fitted. As you know, an Octalink BB has a metal drive-side adaptor which is a fixed part of the BB. You screw the BB into the shell on the drive side and then on the non-drive side you screw in the plastic adaptor (in the opposite direction).

The drive-side adaptor is absolutely flush with the BB shell. On the non-drive side, there is a little amount of thread showing on the plastic adaptor. This suggests that there is scope for a reduction in BB length by a couple of mm i.e. Decathlon could have used a slightly smaller BB

However, the reduction would be on the non-drive side only; a shorter BB would not make any difference on the drive side, which is where the front mech is .

Best regards,

roadbikepilgrim

[Gus T]

Hi Adam, sorry for not

Hi Adam, sorry for not replying earlier, the Octolink BB should  have a size on it, usually on the main body of the BB. If not just measure end to end on the BB and buy 1 a couple of mm’s shorter.

Gus 

[Pub bike]

What is the chainline of your

What is the chainline of your bike?   To find out measure the distance from the frame’s centre-line to the middle of the middle chainring.

According to this the chainline for the Shimano Claris FD-R2030 8 Speed Triple Front Derailleur is 45mm.  The derailleur cannot be expected to work as intended with other chainlines but it may work with some gear combinations, which might be what you are experiencing?

Something else to look at: according to the dealer manual there is a converter on the FD which is adjusted depending on whether you are using a traditional under-BB cable guide or through the frame routing.  See p13 “Adjusting the cable route (FD-R3000/FD-R2000)”.  Worth checking the setting of this and also whether the cable is correctly routed over the securing nut.

[Backladder]

Obviously not the solution I

Obviously not the solution I thought it might be then, I’ll keep thinking about it.

[roadbikepilgrim]

Hi Backladder,

Hi Backladder,

Thanks for your message. Yes, both the Claris double and triple front derailleurs have trim settings (see https://si.shimano.com/en/pdfs/dm/RBFD001/DM-RBFD001-01-ENG.pdf).

However, this dealer manual (which gives the official Shimano setup for both doubles and triples in Claris and Sora) only describes using the trim setting on the large chain ring for the setup of the double front derailleur (pages 19-21), and this is not to reduce noise when in a large ring smallest sprocket combo. The chain actuallyt has to be on the largest sprocket when setting this up.

The point of the trim position is not that it gives you more room at the largest chainring, but that it stops or reduces noise when you are at the large-sprocket end of the cassette. You do not move from the trim position on the large ring to reduce noise when in the large ring smallest sprocket combo. You set up the large chain ring ring with the shifter in the last position, the limit screw set correctly and the cable tension correct to stop noise.

The setup for the triple (which is what I have) is described on pages 22-24. It only mentions a trim setting for the middle chainring in order to have the derailleur in the correct position when setting the cable tension, which is done while in the middle chain ring on a triple.

Best regards,

roadbikepilgrim

[roadbikepilgrim]

Hi Pub bike,

Hi Pub bike,

Thanks for your message. Unfortunately, I need to use the derailleur clamp at it’s full 34.9 mm diamater to go round my seat tube i.e. am using no shims.

So, I cannot try this method.

Best regards,

roadbikepilgrim

[Backladder]

Is there a trim setting on

Is there a trim setting on the shimano front shifter? this usually appears as a fourth click position on a triple shifter and adjusts for precicely this problem, if you have the cable tensioned too much you will never get to the trim position as there is not enough cable to pull before you hit the limit screw. Either test the shifter with the cable slack or back off the tension and try to find an extra click. Note that the extra click could also be on the inner end of the travel and you are out by 1 on the indexing.

[Pub bike]

If you don’t want to or can’t

If your front derailleur is being used with a larger than specified chainline, the geometry of the parallelogram in a given chainring will not be what the designers intended and the mismatch will be more pronounced at the extreme extension towards the large chainring where increasing the cable pull will move the cage less and less further away from the seat tube.  A possible solution is to move the derailleur outwards away from the seat tube so that it is working in its expected operating range.

If you don’t want to or can’t change the bottom bracket (e.g. because Octalink only come in one length) and you therefore have a chainline that is more akin to an MTB (e.g. 50 vs 44mm) you could try this bodge:

Front derailleurs sometimes come with pairs of shims for different size seat tubes.  If you are lucky(?) enough to have a 28.6 seat tube, and you have both shims still inside the FD clamp you could try loosening the cable, and then putting both the shims on the drive side rather than one each on the drive and non-drive side respectively.   Then tighten the clamp securely and adjust the FD cable.

This will move the cage around 2mm across which might give you the clearance you need and restore somewhat normal service.  If it shifts okay in your current setup then this will shift better.

There isn’t much to go wrong but obviously this would be at your own risk.

[roadbikepilgrim]

Hi Gus,

Hi Gus,

Thanks for your message. You raise a very perceptive question.

The bike came originally with a Microshift drivetrain and a Claris Octalink crankset. I replaced the Microshift components with Claris R2000 components, but I left the crankset. My logic for this was that budget bikes sold with a Claris drivetrain in the last few years typically swapped out a Claris hollowtech bottom bracket and crankset for a square-taper bottom bracket and crankset. I concluded that there was no real need for me to replace my Claris Octalink crank. That might have been an invalid conclusion.

As you know, Octalink or square-taper bottom brackets come in varying lengths, whereas Hollowtech bottom brackets do not. I have no idea whether Decathlon fitted the correct length of bottom bracket for the Octalink crank. I believe that they tend to buy in bulk; therefore it is possible that they fitted an Octalink bottom bracket that they had in the factory, rather than one that was the right length for the Octalink crankset and the Microshift front derailleur . Of course, now with a different front derailleur, it is not possible to say whether the bottom bracket is the right length or not for the new front derailleur crankset combination.

Intuitively, what you suggest about using a shorter BB makes sense i.e. it brings the large chain ring inwards and therefore may allow that fraction of extra space to make the difference on front-mech rub. I suppose there are two things that would make me stop before I experimented here:

1) What would be the correct length of Octalink bb to buy? How do I know if I need to go down by X mm in length or Y mm?

2) Would changing the bottom bracket width have a bad effect on chainline, which might have been the reason why Decathlon chose the length of bb they did?

I think I would want to run the idea past a knowledgeable mechanic who could recommend the right length for the BB in my set up. I think the idea has merit; I just would not want to be forking out on different bottom bracket lengths until I found the right one by trial and error!

In addition, as I mentioned in my reply to Rendel, I did a bit of fettling last week with the Claris front derailleur (in effect aligning it as though it were a Microshift front derailleur). This has had the effect of removing a good  lot of the front mech rub. I cannot hear it much now when the bike is in the workstand and obviously it is now even less audible on a ride.

I might be better to let sleeping dogs lie for the present rather than start buying new bottom brackets. I would be interested to know what people / pro mechanics thought of the idea of a smaller bottom bracket, though. If the right one were selected, it might well work nicely.

Best regards,

Adam

[Gus T]

I might be mssing something

I might be mssing something here but is the crank square taper BB or hollowtech? If BB have you tried using a shorter BB, if hollowtech is there a spacer on the drive side that could be moved to the non-drive side?

[roadbikepilgrim]

hawkinspeter wrote:

That’s when you sheepishly turn up to a bike shop and claim that your dog ate your shifter

Ha ha!  Nice one.

Sometimes I wonder whether in Malaysia the factory dog assembled my shifter!

[hawkinspeter]

roadbikepilgrim wrote:

I think I shall wimp out of opening up the shifter. I am bound to find that I cannot get the damn thing back together!

That’s when you sheepishly turn up to a bike shop and claim that your dog ate your shifter

[roadbikepilgrim]

Hi Peter & David,

Hi Peter & David,

Thanks for your messages. I am pretty sure that it is something in the shifter. The shifter will move the chain to all three rings. However when you are on the big ring, there is no further possible movement in the shifter. On a Microshift shifter, unless you have the cable tension and limit stop absolutely right, you can continue to move the shift paddle and the cage will move correspondingly until the limit stop prevents further movement. On the Claris shifter I have, there is absolutely no movement, and it is not the limit stop that is preventing it, and it is not cable tension either. I have to pull on the cable to get further movement, which strongly suggests the limiter is the shifter. What I do not know is whether this is intended design from Shimano, or my shifter has a manufacturing defect.

I think I shall wimp out of opening up the shifter. I am bound to find that I cannot get the damn thing back together!

Regards,

roadbikepilgrim

[mdavidford]

Or, is there flex somewhere

Or, is there flex somewhere in the shifter / setup, so that when the tension is too high it’s flexing instead of pulling?

[hawkinspeter]

Thought I’d stick my oar in

Thought I’d stick my oar in here, despite never having used Claris or Microshift.

The shifter is basically just pulling the cable by a fixed amount, so it’s bizarre that you can manually pull the cable and the cage moves out, but the shifter can’t be made to do that by tightening the cable. I can understand if the shifter pull amount is not quite right, that it can’t properly shift the cage to all three positions, but that doesn’t seem to be what’s happening here.

Could it be that the cable is somehow slipping within the shifter and thus not pulling correctly at higher tension? I’d be tempted to open up the shifter and verify that everything looks to be working properly.

[Author]

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