Originally Posted by nikos
So the bike shop tossed on 2 new rings for my road bike, the inner chain ring (when riding with it) will rub against the larger ring when I shift down to the 2 most outer/lowest cogs? I know I should shift to the larger ring, but that 2nd to lowest is where I like to ride a lot in the smaller ring. The cog is a 6 speed. Is this normal, or could I have some space created between the two rings to open up more room.
Your message is a bit confusing, because the outer sprockets in back are the highest
not the lowest. You shift up
to the smaller rear sprockets.
Generally that is not a good combination to be using for major cruising. Chain and sprocket wear is accellerated in small/small combinations, partly because of the extreme chain angle, and partly just because of the smaller number of teeth engaged.
However, you should
be able to ride in that combination without the chain rubbing.
First off, grab a ruler and measure the chainline to see if it's correct. Standard chainline for a double is 43.5 mm.
if you need instructions in this.
If the chainline is too far to the left, a longer bottom bracket could help, or a spacer washer under the right side mounting ring/cup.
Many cyclists prefer a slightly more inward chainline, which permits the use of more of the rear sprockets with the big ring. I do this myself on some of my own bikes. There is probably a gear combo on your big ring that gives about the same gearing as your small/second smallest gear, only with better chainline and greater efficiency.
Newer "inner" chainrings that are designated "9-speed compatible" tend to have the teeth very slightly offset to the right. This may be the case with yours, but if you're running an older, wider "6-speed" type chain this could explain the rubbing.
Rubbing in the criss-cross gears also is often exacerbated when there's a big size difference betwixt the two chainrings.
If you're due for a new chain anyway, going to a narrower chain may well fix this. (My favorite is the SRAM PC-58)
Adding 5 very thin shim washers between the chainrings could also do the trick.
Sheldon "Straight Chainline" Brown
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