[Irk]

I'll apologize for my ignorance in drivetrain issues right now.

I've been enjoying working (or attempting to) on my bikes and try to take care of everything myself but occassionally I get frustrated and go to the shop.

This was the case when I tried to install a new XTR front derailleur. I'd set the height according to the cage clearance on the large chainring but in doing so the bottom of the cage was hitting the middle chainring by a good 1/8 of an inch. Took it to the lbs because I thought I just wasn't 'getting' something.

They call me back and said that they had to call Shimano and were told by Shimano that the new XTR won't work with anything less than a 44T. The worst part is I just put a new 42T ring on to compensate for the DA 12-27 I am running.

In my limited understanding this seems like a plausible explanation. Is it really and if so doesn't it seem odd that Shimano would do this?

 

[browns110]

I'll apologize for my ignorance in drivetrain issues right now.

I've been enjoying working (or attempting to) on my bikes and try to take care of everything myself but occassionally I get frustrated and go to the shop.

This was the case when I tried to install a new XTR front derailleur. I'd set the height according to the cage clearance on the large chainring but in doing so the bottom of the cage was hitting the middle chainring by a good 1/8 of an inch. Took it to the lbs because I thought I just wasn't 'getting' something.

They call me back and said that they had to call Shimano and were told by Shimano that the new XTR won't work with anything less than a 44T. The worst part is I just put a new 42T ring on to compensate for the DA 12-27 I am running.

In my limited understanding this seems like a plausible explanation. Is it really and if so doesn't it seem odd that Shimano would do this?

This may not be much help, but the old XTR wouldn't work unless you used standard cranks and rings, 110mm. Would not work on compact rings and cranks. Are you running compact cranks?

 

[Irk]

Running compact (RF Next LP)

What is a good alternative for a derailleur when running a 42T on a compact then?

Thanks for the help.

 

[DeeEight]

Derailleur cages are profiled to match the chainring sizes of the group they're sold for to enhance shifting. Larger size rings have less of a curvature to them than smaller rings, for the number of teeth the cage is overlapping. About the only front derailleur maker to ever deliberately profile their cages to work with anything from a 20T to a 48T was the previous Suntour, for their Microdrive groups, but then, they had better shifting derailleurs than shimano did at the time, and could get away with stuff like that (in fact, shimano not only stole a lot of derailleur cage profiles from suntour, they violated several patents in the process of doing so.... which is just a shining example of shimano R&D... steal it from someone else).

 

[Shayne]

I'd just move the deuailleur up another mm or 2

The difference between 44 and 42T is very minimal and both of which are "compact" outer rings reguardless of the bolt circle. There is no reason that the XTR f derailleur shouldn't work with your crankset.

I'm running a derailleur designed for compact rings on a road bike at the moment and it doesnt have a problem with my 50-38-30 chainrings. It just isnt set up according to the manufacturer specs.