Trimming the Gears?

[AuntPetunia]

Hi
Another new road bike question. I just took my bike (cannodale R500 fem) in for its first tune up and service
I was having some trouble shifting gears and was occasionally getting a rubbing noise from the chain.
When they gave me my bike back the Bikes store guy said I needed to trim the gears if it is making the noise -which he explained was sort of a half -shift.
I said OK -but I am still kind of confused about why I need to do this and which gear. Just the rear? Up or down?
Does anyone have any experience with this?
Thanks!

[carback]

I occasionally have to trim my gears as well.

Just a minor 'up' or 'down' on the rear derailleur gears (left hand side shifters (versus right which is your front derrailleur).

I'm not 100% certain why trimming needs to occur but I do know that it is common. Whether to trim up or down is dependent (at least for me) on whether I'm coming into an easier gear or going into a harder gear.

I'm not sure what kind of shifters you have but I just give either the 'higher gear' or the 'lower gear' shifter a slight nudge (usually just an audible click of the gear) and it settles it all out and everything is smooth. Don't worry if you trim the wrong gear. If it doesn't work, try the other gear.

If you trim too heaviily, the worst thing that can happen is that you'll actually change gears completely as opposed to smoothing things out.

I hope I didn't confuse the crap out of you.

[AuntPetunia]

No that helps
I was starting to wonder if there was something wrong with my bike

[Clare]

Hi,

The bike mechanic at the LBS I go to called it a half shift. I have to do it all the time on my Specialize Sequoia.. usually when I'm heading up a hill and I've shifted to the biggest gear (rear) and am on the middle flywheel (front). If I don't, I get a big chain rub, too. I think Carback described the technique well...maybe the LBS can help you out, too.

[emily_in_nc]

Hmmmm, this is interesting. You guys trim the rear derailleur? I nearly always trim my front derailleur rather than my rear. Perhaps this is because I have Campy on one bike and barcons on the other, so in both cases the front is friction shifting rather than indexed. As a result, it's really easy to trim the front to stop chain rub without accidentally shifting to the other chainring (smaller or larger). When I rode a bike with Shimano STI, I couldn't trim the front derailleur worth beans - I would always end up in the next smaller chainring. I really like the Campy and barcon shifting much better.

Emily

[SadieKate]

Usually, the lefthand levers control the front derailleur and everyone has to trim the front derailleur at one time or another if you have a triple. It is just making minor adjustments to keep the derailleur from rubbing the chain when the chain line is at an angle.

Campy has infinite teeny adjustments while Shimano has the "half shift" clicking and is therefore limited to how much it can be trimmed. Having used Campy or barcons for years but just recently learned Shimano road STI shifting I can definitely state that Shimano has more of a learning curve. I'm with Emily on this one.

If you're having to "trim" the rear derailleur, it is out of adjustment.

[AuntPetunia]

Thanks everyone

[carback]

No one ever said I was bright.

I meant the FRONT derailleur is what you're trimming. My apologies if I've completely confused you.

I must stop drinking during working hours.

[shadon]

Usually, the lefthand levers control the front derailleur and everyone has to trim the front derailleur at one time or another if you have a triple. It is just making minor adjustments to keep the derailleur from rubbing the chain when the chain line is at an angle.

Campy has infinite teeny adjustments while Shimano has the "half shift" clicking and is therefore limited to how much it can be trimmed. Having used Campy or barcons for years but just recently learned Shimano road STI shifting I can definitely state that Shimano has more of a learning curve. I'm with Emily on this one.

If you're having to "trim" the rear derailleur, it is out of adjustment.

Hey SK...I think that this might be what you tried to show me how to do at one point on our ride? Am I right?

[SadieKate]

We talked about cross-gearing when your chain is on big/big or little/little front to rear. No amount of derailleur trimming is going to work in this instance. However, the sound of your derailleur rubbing is a good indication that you either need to trim the front derailleur or "uncross" your gear selection. That sound is what alerted me to look at your chain on Sunday.