Front Derailleur Woes

[G3CWI]

Several little problem.

1. When I have the chain on the smallest chain cog and the largest cassette cog (ie closest to the frame) it just touches the inside edge of the front derailleur. The derailleur is correctly aligned but there is no way to stop this rubbing as the derailleur is hard against the frame - no more adjustment. Is this normal on a triple?

2. In hope of fixing the problem described above I had installed a barrel adjuster. As noted above this would not actually help. However I can't get the adjuster to work as both parts turn at the same time. Indeed I can't quite see how they can ever work effectively. I must be missing something obvious.

Shimano 2300 Triban 3.

Bikes seem to be costing me a small fortune with never ending little jobs.

 

[alicat]

Have you tried adjusted the lower stop limits so the front derailleur moves over a little more.

 

[G3CWI]

Have you tried adjusted the lower stop limits so the front derailleur moves over a little more.

Yes. The mech is touching the frame so the screw only moves it away. Therein lies the problem.

 

[RecordAceFromNew]

Several little problem.

1. When I have the chain on the smallest chain cog and the largest cassette cog (ie closest to the frame) it just touches the inside edge of the front derailleur. The derailleur is correctly aligned but there is no way to stop this rubbing as the derailleur is hard against the frame - no more adjustment. Is this normal on a triple?

2. In hope of fixing the problem described above I had installed a barrel adjuster. As noted above this would not actually help. However I can't get the adjuster to work as both parts turn at the same time. Indeed I can't quite see how they can ever work effectively. I must be missing something obvious.

Shimano 2300 Triban 3.

Bikes seem to be costing me a small fortune with never ending little jobs.

Chance is you have the wrong chainline. Was the chainset and/or bottom bracket ever been replaced? If they were then they have likely been replaced by unsuitable components. To double check that what is your current chainline (the distance between the middle chainring and the middle of the frame)? It should be close to 43.5mm.

 

[G3CWI]

Chance is you have the wrong chainline. Was the chainset and/or bottom bracket ever been replaced? If they were then they have likely been replaced by unsuitable components. To double check that what is your current chainline (the distance between the middle chainring and the middle of the frame)? It should be close to 43.5mm.

It's a new bike so that does not seem likely. I will check the distance. Cheers.

 

[accountantpete]

If the front mech is as close to the frame as it can go then either the front mech is incorrectly placed,the chainline is out or the rear wheel has the incorrect dish.

I'd check that the rear wheel is central and if that is ok have a look at putting a small spacer on the freehub before the cassette goes on.

 

[G3CWI]

Where would I get a suitable spacer?

 

[Davidc]

Where would I get a suitable spacer?

Off an old freehub

 

[Hacienda71]

I don't think you should need a spacer on a bike built and set up with that groupset by the manufacturer. Unless you have changed the wheels or other fundamental parts that would seem an odd solution. I know it is a pain, but take it back an Decathlon to sort it. If one of the acceptable gear combinations is not working then the bike is not fit for purpose.

 

[G3CWI]

I don't think you should need a spacer on a bike built and set up with that groupset by the manufacturer. Unless you have changed the wheels or other fundamental parts that would seem an odd solution. I know it is a pain, but take it back an Decathlon to sort it. If one of the acceptable gear combinations is not working then the bike is not fit for purpose.

New wheels!

 

[Hacienda71]

Which wheels?

 

[G3CWI]

Shimano RS20s. Never occurred to me that changing the wheels might cause a problem.

 

[RecordAceFromNew]

Shimano RS20s. Never occurred to me that changing the wheels might cause a problem.

If changing wheels would cause such a problem we would all have the same problem...

Given the front mech cage should be able to clear the chain by at least 1mm, the sprockets will have to be out by 5mm to negate that, and I can't see how adding spacers behind the cassette can be a viable solution - how can one add a 3mm spacer, let alone a 5mm one without running out of thread at the cassette lock ring?

So, if the problem is caused by faulty wheel/hub, it needs surgery. It might be worth checking if the small sprocket is 5mm from the dropout - it should be for an 8 speed cassette.

What is the chainline?

 

[thedatastream]

I have been getting chain rub on my Triban 3 (stock, unmodified) when in smallest front chain ring + biggest rear sprocket on the inside of the front derailleur (i.e. lowest gear)

I attempted to adjust the limit screws on the front derailleur to compensate but they only adjust so far. Why?

Because, as the OP pointed out, the spring for the front derailleur spring rests on the frame and prevents the full range of motion inwards.

Therefore chain rub seems inevitable when in the lowest gear (necessary for West Yorkshire hills!). This is an unmodified Triban as supplied by Decathlon although I have done plenty of miles on it.

Other than buying a new front derailleur that fits better the only thing I can think to do is to shim the chain rings outwards slightly to adjust the chain line at the front? Another 0.5mm ~ 1.0mm ought to be enough.

Sound reasonable or should I be looking elsewhere?

Cheers.

p.s. I haven't measured the chain line yet.

 

[thedatastream]

Additional:

• Not a limit screw issue, the bottom limit screw has a few turns more of adjustment that don't do anything because the derailleur has bottomed out on the frame.
• Not a cable tension issue, the cable is removed at this point
• The derailleur runs parallel to the chainrings, it doesn't appear to be twisted in any way
• Someone else suggested measuring distance from the inside of each crank to the seat tube to see if the crank assembly is centred

ta