Bicycle Mechanics - Which Derailler Do I Need?

I have just swapped the 105 crank on my Trek 520 for an LX crank (44/32/22). The 105 derailler works OK, but I suspect that an LX or XT derailler which is sized for the smaller chainrings would work better. When I checked out deraillers, I saw that Shimano makes LX/XT front deraillers in "top swing" and "bottom swing". What's the difference? Which do I need> Thanks.

OOPS SORRY! FOUND ANSWER IN FORUM AFTER DOING A SEARCH.

I have just swapped the 105 crank on my Trek 520 for an LX crank (44/32/22). The 105 derailler works OK, but I suspect that an LX or XT derailler which is sized for the smaller chainrings would work better. When I checked out deraillers, I saw that Shimano makes LX/XT front deraillers in "top swing" and "bottom swing". What's the difference? Which do I need> Thanks.

OOPS SORRY! FOUND ANSWER IN FORUM AFTER DOING A SEARCH.

Ah, but be advised, as I learned, that you can't toss in a MTB front derailler and expect it to work with your indexed shifter. Has to do with the different amounts of cable pull between road and mt. FD's. (Thanks Sydney). Rivendell has a good little piece on setting up a 105 FD for use with MTB cranks, here's the link
Setting up 105 FD (http://www.rivbike.com/webalog/shifters_derailleurs/17082.html)

I hope this helps.


Steve W.

Ah, but be advised, as I learned, that you can't toss in a MTB front derailler and expect it to work with your indexed shifter. Has to do with the different amounts of cable pull between road and mt. FD's. (Thanks Sydney). But there is no issue with an mtb FD if his 520 has barends or downtube shifters.

THANKS FOR THE INPUT! For the record, I have bar-end shifters. So indexing will not be a problem.

In theory, the MTB derailleur would work better, but I'd suggest you save your dollars and keep your 105. If your chain falls off the small ring sometimes, just lower it a bit and turn it sideways (a bit) so that the bottom part sticks out a bit more than the top part.

For your information, I'm using 44-34-22 with the original 105 derailleur and bar-end shifters. After some 15 000-20 000 km, no problems to report. The only slow shift is when I upshift from the granny to the middle ring.

But there is no issue with an mtb FD if his 520 has barends or downtube shifters.

Are you sure about this? Barends and DT shifters are regulated the same as "brifters"; for road FDs, and that is not the same as an MTB FD.

Are you sure about this? Barends and DT shifters are regulated the same as "brifters"; for road FDs, and that is not the same as an MTB FD. Yeah, sydney is sure,and wasn't smoking carpet when composing that blurb. Barends and downtube front shifters are friction ! They don't know the difference in arm length, type or brand of the FD. :rolleyes: There was one exception I ever saw and that was a set of 6 speed shimano downtubes that did have a friction and INDEX mode for the front lever. Obviously , in the friction mode, it would make no difference if the FD was road or mtb or even some other brand.

Yes, Sidney. Front shifter is friction and rear shifter is either friction or indexed. However, have managed to get the 105 derailler working perfectly. Thanks.

Yeah, sydney is sure,and wasn't smoking carpet when composing that blurb. Barends and downtube front shifters are friction ! They don't know the difference in arm length, type or brand of the FD. :rolleyes: There was one exception I ever saw and that was a set of 6 speed shimano downtubes that did have a friction and INDEX mode for the front lever. Obviously , in the friction mode, it would make no difference if the FD was road or mtb or even some other brand.

Ohmighod, I can't believe I missed that; of course thay are friction , and of course it makes no difference.

Ohmighod, I can't believe I missed that; of course thay are friction , and of course it makes no difference.Ya gotta lay off the carpet dude,otherwise you are doomed to becoming just another nose picking muppet.