Why doesn't my front mech fit without rubbing the chain?

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Location
Rammy
I've been trying all afternoon to get my gears on my mountain bike,

The rear X9 mech went straight on, as did the cassette and cranks however I'm having some trouble with the front mech.

It's a Sram X9 top mount top pull

First issue was that the frame is too skinny for the clamp, this was resolved by wrapping a small bit of inner tube inside the clamp before positioning the mech where described, with the chain guide 3-4mm above the outer chain ring.

If the chain guide is positioned in the correct place then the chain scrapes on the chain guide (the horizontal part) when using the smallest chain ring

If I lower the mech down the seat tube slightly to compensate then the guide hits the largest chainring.

What am I doing wrong?
 

derrick

The Glue that binds us together.
Get the right sized clamp.
 
OP
OP
Black Sheep
Location
Rammy
I've never ever had an issue like this before with any of my bikes, been building and riding for the last 10 years without issue.

Entire components is SRAM, not putting huge chainrings on or anything like that.
 

steve52

I'm back! Yippeee
it either has enough travel for you set up or not, but why would you need the extremes,is small chainring with smallest cog on the rear? or the opposite set up?
 

RecordAceFromNew

Swinging Member
Location
West London
I've been trying all afternoon to get my gears on my mountain bike,

The rear X9 mech went straight on, as did the cassette and cranks however I'm having some trouble with the front mech.

It's a Sram X9 top mount top pull

First issue was that the frame is too skinny for the clamp, this was resolved by wrapping a small bit of inner tube inside the clamp before positioning the mech where described, with the chain guide 3-4mm above the outer chain ring.

If the chain guide is positioned in the correct place then the chain scrapes on the chain guide (the horizontal part) when using the smallest chain ring

If I lower the mech down the seat tube slightly to compensate then the guide hits the largest chainring.

What am I doing wrong?

I would not recommend using inner tube as shim - the cable tension is significant on a front mech and I would be surprised if you current setup is stable in action. If I were you I would get a mech with the right clamp size, and if you insist otherwise modify one of e.g. these (available for different tube and clamp size) from Shimano to fit.

Other things you should check according to this are that the x9 is designed to handle front ring capacity (large - small) up to only 22T, seat tube/chain stay angle of 66-69 degrees. The large ring size is up to only 48T also. You might be violating one or more of them. Finally for both sram and Shimano the recommended cage to large ring clearance is 1 to 3mm.
 
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