[geogecko]

Okay, so I have an XTR FD-M970-E (without BB bracket--it attaches directly to the frame), and I've got everything setup correctly, I think. The RD is working great, the FD is working great, except that the chain is dragging in the bottom of the FD bracket in small chainring/small cog up to the 6th cog, when on the 7th cog, the dragging stops). The FD was factory installed, so I assumed that it was installed correctly (no more mounting plastic piece in the FD).

The problem with adjusting it, is that only one of the two bolts is accessible with the cranks installed.

Oh, this is also a full suspension bike. Some of it goes away if I cycle part of the suspension, which I assume will be the case during normal riding (sag), but not all of it, maybe still 3-4 of the small cogs.

Is there a way to fix this, or is this normal with a FS bike?

 

[lyndonchen]

I have the same rubbing going on with one of my FS. It starts at about the middle gear and get worse with the smaller cogs. Like you say, the amount of sag you run will affect when it starts happening. I'm not bothered by it, I just use the noise as an indicator to shift to the middle ring. If it was a band-clamp type FD I might think about lowering it a little, but it's an E-type.

My other two FS bikes don't have the same issue, at least not as early in the gearing so that I notice it.

 

[geogecko]

Interesting. I thought about the same thing, kind of like a shift light!

Well, after looking at it some more, I'm not sure if this was by design or not, but I figured out how to access the other bolt! Through the hole in the large chainring. The mounting wouldn't allow it to adjust much, but I was able to remove all of the drag except for the last 2 cogs, I figure once I have the recommended 30% sag, it will be fine. Of course I had to set up the FD all over again, but it was worth it...

 

[rmccully]

On my FS bike the same thing happens in my granny chainring when I'm not on the bike. It's only an issue when you're trying to tune the bike. I never have rub when I'm actually riding.

 

[SteveUK]

"...the chain is dragging in the bottom of the FD bracket in small chainring/small cog up to the 6th cog, "

The answer is in the question. The derailleur is not designed to function normally in the small/small combination. You're also putting lateral stress onto your rear derailleur. Shift into the middle ring and drop down a couple on the cassette. There's nothing wrong, per se, you've just found the limitations of your system.

 

[geogecko]

Maybe I should have left it alone then...

Not designed to function? In 6 of the cogs while in the small ring? I could understand the smallest cog or two, but not 6 of them.

 

[SteveUK]

"Not designed to function? In 6 of the cogs while in the small ring? "

Your first post stated that the problem is only permanently evident in the top (highest) three cassette gears, not the top six. It's possible that the derailleur is not fitted correctly, but not being able to use the top three or four rear gears is about right. Of course, it can't be assumed that the derailleur is correctly installed, so I'd recommend starting over with that. Have you also checked to confirm the correct chain length?

 

[FBinNY]

FD cages should be long enough to reach lower than the line from the smallest rear cog to the smallest chainring. This can be important because if you were to run with the chain dragging on the cage it can exert significant stress possibly damaging the derailleur. Remember the upper chord is under tension when you pedal..

On hardtails, this was rarely a problem since the relative postiton of the rear axle and bottom bracket were fixed, and it was easy to get it right. On suspension bikes the height of the bracket is constantly changing and when it's high the chain comes from the cassette at a low angle, possibly too low off the small cog.

You have four choices.

1- Use a larger inner ring.
2- try to lower your FD if possible, or find a front derailleur with a longer cage.
3- if possible, and if it won't comprimise performance, tweak the suspension lower your frame slightly.
4- live with it, being very careful not to tension the chain when it's dragging on the FD cage.

Good luck.

 

[lyndonchen]

I don't think it's a big deal honestly. If the chain is contacting the cage you're going to hear it and probably even feel it. No rider's going to pedal in that combo for long, it practically yells at you to shift out of the granny ring. If you're in the middle of the cassette when it happens, the middle ring easily has the gearing to take over.

 

[Squash]

This is a common...

"non-issue" with many full suspension bikes in the 4" and up travel range. You've hit on the correct solution. You've adjusted the derailleur to eliminate most of the drag and limit it to the smallest two or three cogs in the rear with the suspension fully extended. As long as you can still shift up to the large ring up front with out any portion of the the derailleur cage making contact with the big ring and it perfroms properly you should be good to go. From there the drag on the cage should disapear when the suspension is loaded (i.e. your on the bike) and the sag is set properly.

The reason I say this is a "non-issue" is it really only manifests itself with the bike is in the work stand with the suspension unweighted. Like I said, not really a big deal and actually quite common with many suspension designs.

Good Dirt