Front derailleur rubbing/making noise

[Steve B]

Hi,

Quick question before I start messing with the screws on my front derailleur...

I just replaced my rear cassette. Went from a 11-23 to a 12-27. I have a two ring set up on the
front, a 52 and 39. Since I made the rear cassette bigger, I have been having shifting problems.

The gears seem to shift OK as far as switching gears. However, since the change, the front
derailler now rubs.

Do I need to readjust the front derailleur becase I made the rear cassette larger? Doesn't seem like
this should be the case, but then again, I've been wrong on just about everything on my bike.

Any suggestions? I'd love to hear what you all think before I start messing with the limit screws
etc. Before I added the cassette, the gears/shifting worked perfectly.

Thanks in advance.

 

[Harris]

Steve B <[email protected]> wrote:

> I just replaced my rear cassette. Went from a 11-23 to a 12-27. I have a two ring set up on the
> front, a 52 and 39. Since I made the rear cassette bigger, I have been having shifting problems.

> The gears seem to shift OK as far as switching gears. However, since the change, the front
> derailler now rubs.

> Do I need to readjust the front derailleur becase I made the rear cassette larger? Doesn't seem
> like this should be the case, but then again, I've been wrong on just about everything on my bike.

Under what conditions does the front der rub? Is it only when on the 27T cog? It's not uncommon
for the chain to rub on the large chainring when you're in the small-small combination (39-12,
or 39-13).

If all you changed was the cassette, I would check that the cogs are seated properly on the spline
(especially the smallest cog which can be easily misaligned without realizing it). And make sure the
lockring is tight (40 N-m = 29.5 ft-lb).

Art Harris

 

[Mike S.]

"Steve B" <[email protected]> wrote in message
news:[email protected]...
> Hi,
>
> Quick question before I start messing with the screws on my front derailleur...
>
> I just replaced my rear cassette. Went from a 11-23 to a 12-27. I have a two ring set up on the
> front, a 52 and 39. Since I made the rear cassette bigger, I have been having shifting problems.
>
> The gears seem to shift OK as far as switching gears. However, since the change, the front
> derailler now rubs.
>
> Do I need to readjust the front derailleur becase I made the rear cassette larger? Doesn't seem
> like this should be the case, but then again, I've been wrong on just about everything on my bike.
>
> Any suggestions? I'd love to hear what you all think before I start messing with the limit screws
> etc. Before I added the cassette, the gears/shifting worked perfectly.
>
> Thanks in advance.

Next question: is the f.der. rubbing against the chain? or is the chain rubbing against the
chainrings because you are riding further down the cassette? (riding physically smaller cogs?)

 

[Steve B]

I'll need to check for sure next time I ride, but this is what I recall is happening...

The chain is rubbing against the f.der. I get that kind of repetative, droning, rubbing sound. It
happens when I am in the small front ring at smallER back rings. Like 12-20. It also happens when I
am in the large ring and larger back rings. Like 20-27.

It's almost like the bike is saying, if you want to be in an easy gear, don't use the big ring. If
you want more resistance, don't use the small ring.

I know enough to know that it shouldn't rub in so many gear combos. And as far as tightening the
cassette properly, I don't know the actual torque used, but it's pretty tight. And I made sure the
smallest spline was seated properly.

Thanks for all the advice!

>
> Next question: is the f.der. rubbing against the chain? or is the chain rubbing against the
> chainrings because you are riding further down the cassette? (riding physically smaller cogs?)

 

[Mike S.]

"Steve B" <[email protected]> wrote in message
news:[email protected]...
> I'll need to check for sure next time I ride, but this is what I recall is happening...
>
> The chain is rubbing against the f.der. I get that kind of repetative, droning, rubbing sound. It
> happens when I am in the small front ring at smallER back rings. Like 12-20. It also happens when
> I am in the large ring and larger back rings. Like 20-27.
>
> It's almost like the bike is saying, if you want to be in an easy gear, don't use the big ring. If
> you want more resistance, don't use the small ring.
>

That's probably an accurate assesment based on what you just said. Try shifting back up the cassette
and using the large chainring sooner, and shifting back to the inner ring while going back down 2-3
cogs on the cassette when you need to bail to the inner ring. There's a lot of overlap in gears in
the middle ranges, you're probably not using the right combination yet.

Check it out, let us know.

Mike

> I know enough to know that it shouldn't rub in so many gear combos. And as far as tightening the
> cassette properly, I don't know the actual torque used, but it's pretty tight. And I made sure the
> smallest spline was seated properly.
>
> Thanks for all the advice!
>
> >
> > Next question: is the f.der. rubbing against the chain? or is the chain rubbing against the
> > chainrings because you are riding further down the cassette? (riding physically smaller cogs?)

 

[Harris]

Steve B <[email protected]> wrote:

> The chain is rubbing against the f.der. I get that kind of repetative, droning, rubbing sound. It
> happens when I am in the small front ring at smallER back rings. Like 12-20. It also happens when
> I am in the large ring and larger back rings. Like 20-27.

> It's almost like the bike is saying, if you want to be in an easy gear, don't use the big ring. If
> you want more resistance, don't use the small ring.

It just seems funny that changing the cassette would cause this rubbing if it hadn't been
rubbing before.

BTW, is the chain long enough to handle the larger cogs? And have you tried using the trim feature
on the left shifter to minimize the rubbing?

Art Harris

 

[Steve B]

> It just seems funny that changing the cassette would cause this rubbing if it hadn't been
> rubbing before.
>

That's what I thought, and why I asked the question. The shifting alignment seems OK, so why would
adding larger cogs affect the front der?

> BTW, is the chain long enough to handle the larger cogs?

Yes, I made sure when I added the new chain that it would accomodate the big to big.

And have you
> tried using the trim feature on the left shifter to minimize the rubbing?
>

No, what is this and how do I do it? Is this the grey knob on the down tube?