Chain rub

This post is mostly for me to remember what I did to my bike.

I had noticed that the bike chain was rubbing on the front derailleur when I was in certain gears.  I know this is not supposed to happen and after reading up on it I know that it can affect the life of the chain.  The front derailleur is the area between the pedals that moves the chain if you have different gears in the front.  My bike has 3 gears in the front and 9 gears/cogs in the rear wheel for a total of 27 gears.

I did my due diligence and watched a bunch of videos on YouTube about adjusting your front derailleur as well as reading various DIY bike repair articles on various web sites.  Initially I thought this would be a simple fix.  But I was wrong.  I spent a good part of an afternoon (2-3 hours) futzing with it and only seemed to make things worse.  I ended up giving up that day.  The next day I was determined to try to figure this out and not have to take my bike into the LBS (local bike shop) to have them fix it.  So I basically started from the beginning.

I noticed that the derailleur was actually sitting a little higher than it should.  Everything I read said the bottom of the bracket should be about 2-3 mm from the top of the largest gear.  So I loosened the bracket holding the derailleur to my seat tube and moved the derailleur lower just a little bit.  I also made sure it was parallel to the chain/gears.  I had the chain on the smallest gear in the front and the largest cog in the rear.  Then I adjusted the L screw to make the chain about 1-2 mm from the inside of the derailleur.  I shifted the front chain and it started to rub.  This is where I had the biggest issue.  After further reading, I suspected that the shifter cable tension was the biggest problem.  I loosened the shifter cable from the derailleur and rotated clockwise the barrel adjuster all the way tight (clockwise), pulled the cable tight by the derailleur and tightened it down.  I had the chain in the middle ring on front and middle cog in the back.  I then rotated the barrel adjuster counter-clockwise (which tightens the slack of the cable – this is contradictory to what you would normally think) and watched as the chain moved away from the derailleur and into the center of it so it wouldn’t rub when passing through.  And that was pretty much it.  I didn’t really adjust the H screw, which prevents the chain from jumping off the biggest gear in the front.

I also learned that you want to try to keep the chain straight while riding.  So you don’t want to be in the smallest front chain and in the smallest cog (highest gear) in the rear.  I read when you’re in the smallest gear in front, you want to stay in the back between like gears 1-3.  If you’re in the middle front gear, you should stay in like gears 1-7.  Finally in the largest front gear (hardest), you want to stay in gears 7-9 or so.  That helps keep the chain straight and helps prevent rubbing and I suspect also less tension on the chain since you’re not making it askew.

Went on a short-ish ride today and gears shifted well and everything seemed good with no rubbing.  So we’ll see how it holds up.  I noticed that there was already some fraying of the shifter cable (which is surprising since I’ve had this bike for 1 year and hadn’t rode it much but maybe just a sign that things made these days don’t last, or the LBS that I bought it from doesn’t use high quality stuff…oh well, when it comes time I’ll figure out how to change the cable as well).



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