derailleurs and barrel adjusters
 

my bike has sti 105 components and the inline barrel adjusters on the down tube. there is another barrel adjuster located next to the rear derailleur. what is the purpose of the inline adjuster other than to confuse me when i am trying to set my index shifting? no manuals i have seen explain this...

My inline downtube cable adjuster for the rear der. cable has a little lever and click-stops but the right one is just a traditional one with the "pull-me" like the rear der. barrel adjuster. This leads me to believe that it's simply there for quick on-the-fly adjustment so you can temporarily fine tune things without stopping.

Why a barrel adjuster on the downtube (or sometimes on the shifter) and another one on the rear derailleur?

Mostly to give you more opportunity to adjust the cable. It becomes especially handy on tandems or triplets, where the rear cable is especially long.

Basically, when you install a new cable, screw in as much as possible the barrel adjuster which is on the derailleur, and screw in almost to the maximum the one on your downtube. That way, you will maximise adjustment possibilities.

Regards,

Regards,

I don't know about anyone else, but I've never had any luck with the cable adjusters on the downtube. I always wind up having to make the adjustment at the rear derailleur to get things right.

I only used the downtube adjuster for my rear der. once and it was a temporary quick-fix during a long downhill. I did end up resetting it and adjusting the rear at the next stop though. For the front der, you have no choice but to use the downtube barrel adjuster or on some bikes the inline ones near the brifters.

On my bike, one click of the secondary adjustment equals about a quarter turn of the rear barrel.

Though less of a problem than it used to be, cables still do stretch. Generally this exhibits itself as a slower than normal upshift to the larger sprockets. The secondary adustment lets you fine tune the indexing without stopping the bike.

The down tube barrel adjuster on the left side (front derailleur) is useful if you have a triple. It allows you to fine tune the middle chainwheel. Counter clockwise moves the chain plate out and clockwise in. This works well when you are in the middle chainwheel and the smallest cog by allowing you to stop the rubbing of the chainplate. Good luck.