front derailleur cage width?

[pinchflat]

Howdy all... I think my Deore front D has a wider distance between the inner and the outer plates than does my Deore LX, on the order of .1"

With the chain on the front mid ring, the bike with the wider gates (Deore) will tolerate a rear shift from 1 to 9 without the chain rubbing on the front plates, and the bike with the narrower gates (Deore LX) will rub on 3rd and 7th.

I can't find this spec listed on Shimano's site. Does anyone have a reliable source of this width? Or measurements of this width for the SRAM line? Thanks

 

[gclark8]

The LX is the better.

And it is not set up correctly if I read you right. The mark of a good derailleur is its shift performance, not its cross chaining ability.

There should be a "trim" position in the middle range of the shifter.

 

[pinchflat]

The LX is the better.

And it is not set up correctly if I read you right. The mark of a good derailleur is its shift performance, not its cross chaining ability. There should be a "trim" position in the middle range of the shifter.

the derailler shifts fine but I'd like to, briefly, access the extremes of the cassette (at the expense of more chain and tooth wear) as my other bike with the same components but different frame and front Deore derailler can do this. I've since gotten accurate measurements on another Deore, and I now believe it is the same width as the LX, so I'm now down to something like chain line to explain the difference in shift behavior.

I've fiddled the LX back and forth, and, on mid ring can generally shift thru maybe 5 cogs on the rear cassette without dragging against either side of the front D's cage. These 5 can be 1 thru 5 on the low speed end or maybe 4-9 on the high side. I'm currently setting things such that the big ring is ok on maybe 3 thru 8, and I'll hold it over with the shifter is I need 9th. Ok, but limiting.

I'm guessing for this bike frame/crankset/cassette/ front derailleur combo, geometry sez I'm only going to get 5 noise free rear cogs. I can manually hold the front cage over with the shift lever to get a little more range but is there something similar for pulling the cage back towards the bike (loosening the shift cable?) ?

I don't understand the "trim" position on the front shifter: should I be able to get multiple clicks/positions as I push the D cage towards a larger ring? This is a standard Deore 3 position front shifter.

thanks

 

[scirocco]

The mark of a good derailleur is its shift performance, not its cross chaining ability.

Says who? A comment like that can only come from someone who spends his life explaining to customers why they have this grinding noise coming from their front derailleurs.

In my experience, there is not much difference in shift performance between any of the mid-range to top end FDs, but there can be a wide difference in cross-chaining ability. Not having to trim the FD every few times you change gear is certainly highly desirable in my book.

To the OP; I've found minor differences in mounting or placement of the FD can make a big difference to the degree of chain rub. I have a braze-on Ultegra FD that is significantly worse than a band-on Tiagra one, simply because the braze-on clamp positions the FD more rearwards. Yet shifting performance is identical.