My front chain hits my derailleur?

Question

I've taken my bike back to the place where I bought it to have a look at my front derailleur, and it's still bad. I've adjusted my high and low settings when in first and third gear respectively so that the chain is not touching the derailleur. In both cases when i change my back gear to the opposite end of the gears, it hits the derailleur on the other end just slightly.

there seems to be no win, if I change my high or low anymore the chain will hit the derailleur even more. Can anyone help me with this?

my bike is a diamonback and my gears are shimano

Answer 1

Are you having the same trouble with your rear chain, or just your front?

How many chains does your bicycle have?  Other than on tandems, my experienced is limited to single chain bicycles.

Sorry.

Answer 2

I had this same problem with my derailleur a few seasons back. What I found was that even after adjusting the h**l out of the high and low limiter screws, the chain would still rub when I was in top gear or in lowest gear. What I did that seem to work for was adjust the barrel adjuster which changes the tension in the shifter cable.

First, set the limiter screws for the high and lowest gear for the your crankset (these screws are meant slowly to limit the movement of your derailleur - i.e. keeping your chain on your cogs/or from over shooting the gear).

Second, put the bike in the lowest gear possible to relieve the cable of all tension (so it's almost slack, you can check this by using your finger and plucking it).

Third, locate the tube that is holding the cable for your front derailleur and follow it up until you see the barrel adjuster and turn counter clockwise (start with 1/4 turns). The shifter cable should have more tension now.

Fourth, cycle the bike back up to top gear and see if the adjustment was enough.

Repeat until the chain clears the derailleur by approx.1-2mm in top gear.

I hope this helps you.

A.

Answer 3

That's because you shouldn't be using the big chainring, big rear sprocket combination.  Likewise you shouldn't use the small chainring , small rear sprocket combination.  Either of those will place your chain at an extreme crossover angle that will wear your gears and chain out prematurely. As an example shift your bike into the big big combo and look at the chains path from the rear of the bike. See how it goes from one side to the other? That's not good.

Stop messing with your front derailleurs limit s***w settings. Once they're set they shouldn't need any further adjustment. When you're in the very lowest gear ... small front, big rear ... the chain should just clear the inside edge of the front derailleur cage. When in the big front, small rear sprockets the chain should just clear the outside edge of the cage. Any further adjustment to the front derailleur is done by the angle and height of the mechanism relative to the chainrings and, of course, cable tension.

If you still don't understand the concept of chain angle go back to your shop and have them explain it to you. Also have them explain how gear ratios are calculated, what they mean as far as pedaling effort and distance traveled, and how some of every bikes gear ratio combinations actually result in duplicates. There's no reason to use the extreme combinations because there are other gears that will give you a duplicate ratio.

Best to go at a time when they are not busy as this may take awhile to explain. Maybe a rainy weekday morning?