45 mm chainline with a *mountain* Front Derailleur?
#1
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
45 mm chainline with a *mountain* Front Derailleur?
I've got a Surly Long Haul trucker that I just tried to put a new Front Derailleur on.
The old Deore XT front derailleur shifted my 44 tooth tripple just fine, but it need replacing.
The Xt FD-M770 Front Derailleur that I just tried to put on wouldn't go inboard enough.
I did a bit of internet research, and measuring, and it turns out when my bike was built for me, it was set up with a 45 mm chainline. (the new derailleur is meant for a 50mm chainline, and can't move inboard enough for me)
Are there any Front Derailleurs out there that would be able to handle a 44 tooth max chainring at 45mm chainline?
Thanks,
Leslie
The old Deore XT front derailleur shifted my 44 tooth tripple just fine, but it need replacing.
The Xt FD-M770 Front Derailleur that I just tried to put on wouldn't go inboard enough.
I did a bit of internet research, and measuring, and it turns out when my bike was built for me, it was set up with a 45 mm chainline. (the new derailleur is meant for a 50mm chainline, and can't move inboard enough for me)
Are there any Front Derailleurs out there that would be able to handle a 44 tooth max chainring at 45mm chainline?
Thanks,
Leslie
#2
Banned
chainline refers to the crank/BB spindle length.. in reference to the back
the middle cog on the back and the middle chainring on the crank are in a line parallel
to the center line of the bike.
hit the bike shops .. ask .. bring the bike
FD wont go in far enough?, you need to move the crankset chainline further outboard.
the middle cog on the back and the middle chainring on the crank are in a line parallel
to the center line of the bike.
hit the bike shops .. ask .. bring the bike
FD wont go in far enough?, you need to move the crankset chainline further outboard.
Last edited by fietsbob; 05-15-13 at 11:13 AM.
#4
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
These are great suggestions. I have a Phil Woods BB right now, that I am loath to change.
My first choice would be to keep my current chainline (and thus keep my current BB) and find a derailleur that works with it.
I have read that road derailleurs are meant to work with a 45mm chainline, Does anyone know if I can run a road deraileur with a 44 tooth triple crank? (and a 22 tooth difference in the front)?
I've never used a road derailleur, so I don't know.
My first choice would be to keep my current chainline (and thus keep my current BB) and find a derailleur that works with it.
I have read that road derailleurs are meant to work with a 45mm chainline, Does anyone know if I can run a road deraileur with a 44 tooth triple crank? (and a 22 tooth difference in the front)?
I've never used a road derailleur, so I don't know.
#5
Low car diet
Join Date: Aug 2007
Location: Corvallis, OR, USA
Posts: 2,407
Bikes: 2006 Windsor Dover w/105, 2007 GT Avalanche w/XT, 1995 Trek 820 setup for touring, 201? Yeah single-speed folder, 199? Huffy tandem.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 4 Times
in
4 Posts
- Different cable-pull ratio between road and MTB front shifters/derailers. This can be remedied by using a Shimano "flat-bar road" FD, which is a road FD in most respects, but uses MTB cable-pull ratio.
- Chainring sizes, as you mentioned. The curvature will be different. IME, this issue has more to do with shifting performance over compatibility per se.
- Chainstay angle. Road FDs typically call for a 63-66 angle--and MTB 66-69 angle--between the chainstay and seat tube. (MTB bottom brackets are higher, widening the angle). Operating outside this range can affect things, though I don't know exactly how.
Currently, I'm using a road front derailleur on 22/38/bashguard chainrings with 47.5 mm chainline on my MTB turned touring bike with front road shifter (105 STI) and 8-speed cassette. I tried using a large chainring (can't remember now if it was 48, 44, or 42) but I just couldn't set it up so that I could use each chainring how I wanted to. I can't remember exactly, but I think to use the highest gear (big chainring/smallest cog) I had to increase the cable tension to the point that I couldn't use the middle chainring with several of the largest cogs. I tried several heights and angles of the FD. I don't know if it was the chainring sizes, chainstay angle, both, or neither.
Ultimately, I decided I didn't need the largest chainring and replaced it with a bashguard and it works very well now: in the 38T, I can use all cogs (though avoid the largest), and the 22T can be used with as many as I want it to (at least half..I couldn't tell you the limit unless I test it).
(By the way, the above issues nearly become non-issues with a friction front shifter.)
#7
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
#8
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
Chainring sizes, as you mentioned. The curvature will be different. IME, this issue has more to do with shifting performance over compatibility per se.
- Chainstay angle. Road FDs typically call for a 63-66 angle--and MTB 66-69 angle--between the chainstay and seat tube. (MTB bottom brackets are higher, widening the angle). Operating outside this range can affect things, though I don't know exactly how.
- Chainstay angle. Road FDs typically call for a 63-66 angle--and MTB 66-69 angle--between the chainstay and seat tube. (MTB bottom brackets are higher, widening the angle). Operating outside this range can affect things, though I don't know exactly how.
How much of a shifting performance loss is there due to the difference in curvature of a road front derailleur vs my 44 tooth chainring?
Does the seat tube angle make much difference at all in front derailluer function?
My Surly is listed as having a 72 degree seat tube, but my old Deore XT front derailleur seemed to work fine.
Thanks again, this is all really helpful.
#9
Senior Member
Join Date: Apr 2010
Posts: 75
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
A trekking series will work, FD-t671. It is specifically designed for road bikes with flat handlebars. It is 66-69 degree and has related 44 and 48 max chainring cranks. Works with related flat bar shifters. I have not tried in real life, as not available in north America, you need to order from Europe. Shimano only want us NA's to be racing and has no recognition of other uses for bikes. I am now looking at SRAM.
#10
Low car diet
Join Date: Aug 2007
Location: Corvallis, OR, USA
Posts: 2,407
Bikes: 2006 Windsor Dover w/105, 2007 GT Avalanche w/XT, 1995 Trek 820 setup for touring, 201? Yeah single-speed folder, 199? Huffy tandem.
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 2 Post(s)
Likes: 0
Liked 4 Times
in
4 Posts
Thanks for the detailed info!
How much of a shifting performance loss is there due to the difference in curvature of a road front derailleur vs my 44 tooth chainring?
Does the seat tube angle make much difference at all in front derailluer function?
My Surly is listed as having a 72 degree seat tube, but my old Deore XT front derailleur seemed to work fine.
Thanks again, this is all really helpful.
How much of a shifting performance loss is there due to the difference in curvature of a road front derailleur vs my 44 tooth chainring?
Does the seat tube angle make much difference at all in front derailluer function?
My Surly is listed as having a 72 degree seat tube, but my old Deore XT front derailleur seemed to work fine.
Thanks again, this is all really helpful.
It's not the seat tube angle per se, it's the angle between the seat tube and chainstay (as it affects the angle of the FD relative to the line between the chainrings and cog).
HOWEVER, since you have friction front shifting, the issues I brought up probably won't even apply anymore. It's indexed front shifting that's finicky.
I have limited personal experience with friction front shifting, but from what I've read, people have used pretty much any friction front shifter with any FD and it's worked. The only possible issue is whether the total amount of cable the shifter can move is enough to allow the FD to move across all chainrings. But, I just haven't seen this actually be a problem.
You may need to play around with the vertical position for the FD. I'd make sure that I could find a spot for the shifter so that the chain on the middle chainring doesn't rub on the cage no matter which cog was used in back (save one or both extremes).
Otherwise, set up the FD normally. For friction, you really just need to set the Limit screws so you don't overshift in either direction.
Last edited by JiveTurkey; 05-16-13 at 05:03 PM.
#11
Senior Member
Join Date: Apr 2011
Posts: 336
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I have limited personal experience with friction front shifting, but from what I've read, people have used pretty much any friction front shifter with any FD and it's worked. The only possible issue is whether the total amount of cable the shifter can move is enough to allow the FD to move across all chainrings. But, I just haven't seen this actually be a problem.
#12
Retro Grouch
Join Date: Oct 2007
Location: Santa Cruz
Posts: 2,210
Bikes: Yes
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
The proper fix is a wider BB; your Phil Woods BB is adjustable, so you may be able to simply move it over a few millimeters.
Otherwise, which older XT derailleur worked for you? It may be as simple as finding one in better condition ..; otherwise you will need to jump through some hoops, hoping a derailleur not designed for your setup will work. The old XT derailleur also fits that bill, you just know it works.
Otherwise, which older XT derailleur worked for you? It may be as simple as finding one in better condition ..; otherwise you will need to jump through some hoops, hoping a derailleur not designed for your setup will work. The old XT derailleur also fits that bill, you just know it works.
Last edited by onespeedbiker; 05-17-13 at 08:35 PM.
#13
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
#14
Member
Thread Starter
Join Date: Feb 2008
Location: Brampton, ON, Canada
Posts: 44
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 0 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
The proper fix is a wider BB; your Phil Woods BB is adjustable, so you you may be able to simply move it over a few millimeters.
Otherwise, which older XT derailleur worked for you? It may be as simple as finding one in better condition ..; otherwise you will need to jump through some hoops, hoping a derailleur not designed for your setup will work. The old XT derailleur also fits that bill, you just know it works.
Otherwise, which older XT derailleur worked for you? It may be as simple as finding one in better condition ..; otherwise you will need to jump through some hoops, hoping a derailleur not designed for your setup will work. The old XT derailleur also fits that bill, you just know it works.
However, finding another identical XT derailleur in good condition that would work is a great idea. The problem is I don't know how to find the part number. The bike was built in 2008. The derailleur says "Deore XT" on it. It has a 28.6mm clamp (bottom clamp traditional style derailleur).
But I can't even find a Shimano lookup table that would tell me 2007/2008 parts lists.
I'll try to take a photo of it when I get home and post it. But without knowing the part number, I don't know how to even search for a used one.
Good suggestion though.
#15
Retro Grouch
Join Date: Oct 2007
Location: Santa Cruz
Posts: 2,210
Bikes: Yes
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
I'm really hoping I can find a fix without changing chainline (I like 45mm it really is the "ideal" straight line from the middle chainring to the middle cassette sprocket on a 9 speed cassette - and I use all chainrings with all gears)
However, finding another identical XT derailleur in good condition that would work is a great idea. The problem is I don't know how to find the part number. The bike was built in 2008. The derailleur says "Deore XT" on it. It has a 28.6mm clamp (bottom clamp traditional style derailleur).
But I can't even find a Shimano lookup table that would tell me 2007/2008 parts lists.
I'll try to take a photo of it when I get home and post it. But without knowing the part number, I don't know how to even search for a used one.
Good suggestion though.
However, finding another identical XT derailleur in good condition that would work is a great idea. The problem is I don't know how to find the part number. The bike was built in 2008. The derailleur says "Deore XT" on it. It has a 28.6mm clamp (bottom clamp traditional style derailleur).
But I can't even find a Shimano lookup table that would tell me 2007/2008 parts lists.
I'll try to take a photo of it when I get home and post it. But without knowing the part number, I don't know how to even search for a used one.
Good suggestion though.
or the back of the plastic piece where the adjustment screws are..
#16
Senior Member
Join Date: Apr 2006
Location: Escondido, CA
Posts: 2,240
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
45 mm is the standard road triple chainline. If your bike worked correctly for you with a Deore XT FD and a crank with a 44T big ring (presumably a mountain bike crank) and they were both set at 45 mm, getting that to work involved some black magic and possibly some custom parts.
The easiest solution would be to live the crank alone and to get a new road FD. I think that a current Shimano FD should work correctly, especially since you have a friction front shifter.
The easiest solution would be to live the crank alone and to get a new road FD. I think that a current Shimano FD should work correctly, especially since you have a friction front shifter.
#17
Retro Grouch
Join Date: Oct 2007
Location: Santa Cruz
Posts: 2,210
Bikes: Yes
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
45 mm is the standard road triple chainline. If your bike worked correctly for you with a Deore XT FD and a crank with a 44T big ring (presumably a mountain bike crank) and they were both set at 45 mm, getting that to work involved some black magic and possibly some custom parts.
The easiest solution would be to live the crank alone and to get a new road FD. I think that a current Shimano FD should work correctly, especially since you have a friction front shifter.
The easiest solution would be to live the crank alone and to get a new road FD. I think that a current Shimano FD should work correctly, especially since you have a friction front shifter.
#18
Senior Member
Join Date: Apr 2006
Location: Escondido, CA
Posts: 2,240
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 1 Post(s)
Likes: 0
Liked 0 Times
in
0 Posts
I have a road front derailleur and a 42T large chain ring on my bike and I haven't observed any issues so far. (Maybe I'm not trying hard enough?) There's nothing in the specs for my FD about the size of the large chain ring. Unlike, say, the gap between small & large.
#19
Expired Member
Join Date: Jun 2007
Location: TN
Posts: 11,499
Mentioned: 37 Post(s)
Tagged: 0 Thread(s)
Quoted: 3649 Post(s)
Liked 5,382 Times
in
2,732 Posts
Are you sure you don't have something keeping the new XT from retracting all the way? Limit screw, cable, spacer of some sort? For the time period, 9 speed, seems like your new FD should not be so different.
#20
Retro Grouch
Join Date: Oct 2007
Location: Santa Cruz
Posts: 2,210
Bikes: Yes
Mentioned: 0 Post(s)
Tagged: 0 Thread(s)
Quoted: 3 Post(s)
Likes: 0
Liked 1 Time
in
1 Post
[h=3]Large-Chainring Size[/h] Front derailers shift best when they are mounted as low down as is possible without having the cage foul the teeth of the chainrings. In particular, the bottom edge of the outer cage plate should be closely matched to the curvature of the largest chainring.
If you use a front derailer with a larger ring than it is meant for, the rear of the cage will get too close to the chainring before the front of the cage is close enough to provide crisp shifting.
If you use a front derailer with a smaller ring than it is meant for, the front of the cage will get close to the chainring while the rear of the cage is still far away from it. This won't hurt shifting, but will require excessive "trimming " of the front derailer as you change gears at the back.
Mismatched derailers and chainrings may be satisfactory with friction shifting, but will likely cause problems when used with indexed shifters, such as Shimano STI units.
If you have unusual gearing requirements, and are handy, you can reshape the outer cage plate with a grinding wheel to match a non-standard large chainring. https://sheldonbrown.com/front-derailers.html#chainring
As far as not showing up up in the tech docs, Shimano gives you a list of the cranksets that are appropriate for the front derailleur; these cranks fall within the range the front derailleur is designed for. Further, if you check the Shimano Flat Bar gruppo, you will find MTB derailleurs that have a cage rating for larger chainrings. Even then, Shimano has one front derailleur for a 50T chainring crankset and another for a 52T chainring crankset https://techdocs.shimano.com/techdocs...&bmUID=jWLY1Rz
Thread
Thread Starter
Forum
Replies
Last Post
fuji8
Bicycle Mechanics
9
06-06-13 12:39 AM