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Discussion Starter · #1 ·
As the tittle suggests, you may imagine the rest of the story so this is my set up;
Middleburn rs7 cranks & spider, Middleburn slick-shift chainrings (22-32-44)
Sram X.9 FD clamped to Blur LT2 (which uses a 73 x 113 bb...)

First of all, I have tried all kind of set ups, move the FD cage up & down, left & right and so on. Now the FD is placed as it should be, 1mm or 2mm above the big ring and the cage is paralell to the chainrings which are not bent... so in theory, everything is in well condition and well placed...but no matter how I adjust the FD that the chain ONLY rubs when I use the middle ring and the smallest or biggest sprocket (so I'm not getting chain rubbing neither in the granny nor the big chainring)...I've played either with the shifter barrel and the limit screws but nothing seems to work and if I get rid of the rubbing then I drop the chain when shifting to the big ring or from middle to small ring.

So, my questions are...are there more things to look for to avoid rubbing such as the chainring number of teeth or the thickness of the chainrings or something like that or should I live with that?? after lots of fine tuning, I've managed to get rubbing only using middle ring and smallest sprocket....
 

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Discussion Starter · #4 ·
I've just found out that the chains rubs against the big chainring inner side when I'm in the middle ring & small sprocket, so some of the noise coming from the drivetrain (and that I thought it was chain rubbing with the FD) is caused by that, is that normal??chainrings aren't bent!
 

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Depending on things like chainstay length and chainline, it isn't all that rare for the chain to rub on the outer ring when using the middle ring with the outermost rear sprocket. It isn't fixable except by things like changing chainline, and/or increasing the separation between the chairings.

Similarly even a perfectly adjusted FD will often rub the chain when it comes from the extreme inner or outer angles. If the chain only rubs the FD cage when using the middle chainring with either the innermost or outermost sprockets, or especially with both, that's evidence of a perfect FD trim and all you'll get out of your system.

Micro adjust FD controls allow you to trim the FD position to solve the cage rub problem, but otherwise consider that and the rubbing on the outer ring with the smallest sprocket characteristics of your bike and learn to work around them.
 

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Discussion Starter · #7 ·
this answer makes things clear, cheers for that, at least I've been be able to adjust my FD properly...Regarding the chain rubbing, it seems I'll have to live with it....:rolleyes: :rolleyes:
FBinNY said:
Depending on things like chainstay length and chainline, it isn't all that rare for the chain to rub on the outer ring when using the middle ring with the outermost rear sprocket. It isn't fixable except by things like changing chainline, and/or increasing the separation between the chairings.

Similarly even a perfectly adjusted FD will often rub the chain when it comes from the extreme inner or outer angles. If the chain only rubs the FD cage when using the middle chainring with either the innermost or outermost sprockets, or especially with both, that's evidence of a perfect FD trim and all you'll get out of your system.

Micro adjust FD controls allow you to trim the FD position to solve the cage rub problem, but otherwise consider that and the rubbing on the outer ring with the smallest sprocket characteristics of your bike and learn to work around them.
 

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ban said:
this answer makes things clear, cheers for that, at least I've been be able to adjust my FD properly...Regarding the chain rubbing, it seems I'll have to live with it....:rolleyes: :rolleyes:
You don't so much as live with it, as work around it.

Combinations where the chain feeds at greater angles are less efficient due to higher friction between the chain and the sides of chainwheel teeth. They're also harder on the chain.

You don't actually lose anything by avoiding these combinations because simialr ratios can usually be achieved with the next chainring and a more aligned cassette sprocket.

I'm not saying never to ride them, but to avoid and work around these crossed chain combinations. After a while it becomes automatic, and you don't miss them.
 

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Discussion Starter · #9 ·
Yes you're right again! I was already avoiding using the smallest sprocket with middle ring because of the rubbing so what I meant to say with " I'll have to live with it" was precisely what you say, get used to avoiding those ratios as well as you are always told not to use for example smallest sprocket with granny...but at least, I'm relieved in the sense that the FD is set properly, so cheers again!:thumbsup: :thumbsup:
FBinNY said:
You don't so much as live with it, as work around it.

Combinations where the chain feeds at greater angles are less efficient due to higher friction between the chain and the sides of chainwheel teeth. They're also harder on the chain.

You don't actually lose anything by avoiding these combinations because simialr ratios can usually be achieved with the next chainring and a more aligned cassette sprocket.

I'm not saying never to ride them, but to avoid and work around these crossed chain combinations. After a while it becomes automatic, and you don't miss them.
 
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