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Old 02-27-08, 08:49 PM   #1
Butterthebean
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front derailler "reach"

Having a problem on my latest build. I have a old Shimano Altus LT front der on a lugged steel frame, with friction shifters. The BB is a Shimano square taper 127mm cartridge type. I took off the old double crank to replace with the triple (a Sugino GP 52-42-32, 170mm), now the derailler doesn't haven't enough throw to reach either the inner or outer chain rings. I've backed off both limit screw till they are not even touching when I shift all the way, but still...it seems this derailler doesn't have enough reach. I've checked and the derailler cable is tight. I have a newer derailler I could put on there, but the derailler that's on there is the old style that has a casing stop on it. I also have to use a cable/casing guide on the down tube as well.

Only possible solution I can think of to that problem would be to replace the down tube cable guide with a more modern cable guide under the BB shell...allowing me to go to a more modern derailler.

But really, what fun is that. I'd rather keep the current setup if I can. Any options???
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Old 02-27-08, 09:21 PM   #2
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Because chainline on a double crank is calculated from the center space between the chainrings, and a triple is calculated from the center ring, the triple usually requires a shorter BB spindle. The issue isn't the FD reach, it's your chainline.
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Old 02-27-08, 09:34 PM   #3
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You may need a triple front derailleur with a wider cage.
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Old 02-27-08, 09:37 PM   #4
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as Wordbiker said your 127mm BB is far to wide......
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Old 02-27-08, 10:50 PM   #5
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Granted...the 127mm BB is pretty darn wide, but the derailler doesn't reach the large chainring now. If I put a shorter BB in there, how will that help it reach the large chainring? Seems to me, it will make it even harder to reach the large chainring. I know this because I put an 122mm BB in there and that's what happened.
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Old 02-27-08, 10:58 PM   #6
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Originally Posted by Butterthebean View Post
Granted...the 127mm BB is pretty darn wide, but the derailler doesn't reach the large chainring now. If I put a shorter BB in there, how will that help it reach the large chainring? Seems to me, it will make it even harder to reach the large chainring. I know this because I put an 122mm BB in there and that's what happened.
I lost you there. A shorter BB spindle will move the chainline inboard, no? Which means that the big ring will be moved inboard. Which means the FD should reach it easier.

- Mark
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Old 02-27-08, 11:28 PM   #7
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I lost you there. A shorter BB spindle will move the chainline inboard, no? Which means that the big ring will be moved inboard. Which means the FD should reach it easier.

- Mark
Right....my mistake. It's late and I've been thinking about it too much. It should reach the outer chain ring easier with a shorter BB. What I meant to say was, it will then not reach the inner (smallest) chainring. Of course, it really doesn't reach it now.

There's the problem. I can't reach all three chainrings at the same time.

I think I'm going to have to go with a new triple front derailler, and add a cable guide to the bottom of the BB shell.
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Old 02-27-08, 11:50 PM   #8
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Your current DER probably doesn't have enough reach for 3 rings.
It's optimized for a double and probably works far better in that mode, than a triple DER would on a double chain ring bike.
I had fairly recent experience in using 2 bikes with doubles and 2 with triples. The doubles shift MUCH nicer. I think it's probably because the double has better mechnical advantage, The cage doesn't have to move as far per amount of shift lever travel.

You say the cable is tight. Maybe not enough slack? Set the low limit screw so the chain barely goes on the small ring, loosen it 1/4 turn more and then loosen the cable clamp and retighten. You just want the "slop" out of the cable, but not "tight".
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Old 02-27-08, 11:57 PM   #9
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Right....my mistake. It's late and I've been thinking about it too much. It should reach the outer chain ring easier with a shorter BB. What I meant to say was, it will then not reach the inner (smallest) chainring. Of course, it really doesn't reach it now.
No problem, I get confused easily myself.

If after having both the high and low limits backed all the way out, you can't reach either the big ring or the small ring, this sounds like your FD simply doesn't have the reach to do the job and/or your levers aren't pulling enough cable. Obviously moving the chainline by a different spindle length of your BB is going to help in one direction but it can't help in both.

These sorts of things are why I've stayed away from double to triple conversions. Lots of gotchas. Any interest in a compact double?

- Mark
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Old 02-28-08, 07:12 AM   #10
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No problem, I get confused easily myself.

If after having both the high and low limits backed all the way out, you can't reach either the big ring or the small ring, this sounds like your FD simply doesn't have the reach to do the job and/or your levers aren't pulling enough cable.



- Mark
Well, that brings up another question. The shifters I'm using are these...

http://www.loosescrews.com/index.cgi...id=13138721611

cheap, stem mounted friction shifters. They are perfect for this budget build. Would some newer bar ends have more cable pull? I wanna stay with friction, and I don't want downtube shifters...mainly because I'm to old/stiff/fat to reach down that far to shift every time. But some bar ends might be okay, as long as they fit in my moustache bars.
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Old 02-28-08, 08:31 AM   #11
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When you switch from double to triple, you also need to change bottom brackets. In my experience, the BB spindle for a triple is always longer, about 5 mm. or so. A triple front derailleur will also shift a lot better becuase the profile will match the rings better. You can get a Sora for ~$20.
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Old 02-28-08, 11:47 AM   #12
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Well, that brings up another question. The shifters I'm using are these...

http://www.loosescrews.com/index.cgi...id=13138721611

cheap, stem mounted friction shifters. They are perfect for this budget build. Would some newer bar ends have more cable pull? I wanna stay with friction, and I don't want downtube shifters...mainly because I'm to old/stiff/fat to reach down that far to shift every time. But some bar ends might be okay, as long as they fit in my moustache bars.
I love Barcons and the common Shimano ones (Ultegra I think) commonly available on Ebay fror $20-$40 can be set up for friction or indexed. I'm running them on my old Trek indexed in the rear and non-indexed in the front. I assume they'd work great on a triple, although I don't know for sure.

On the possible cable pull problem, do your current levers move the FD through it's full range right up to the backed out limit screws? Moving towards the big ring, after you pull the lever all the way back, can you by hand move the cage further out?

- Mark
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Old 02-28-08, 01:12 PM   #13
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The Altus LT, intended for a double crank, won't work for a triple crank, it won't move far enough. At least that's the case if it's the model I'm thinking of. Altus LT was original equipment on my 1983 Schwinn le tour luxe.

As for the chainline, you need to fix that with a different bottom bracket spindle length. Different cranks use different lengths, with triples generally requiring longer spindles, all other things being equal. Sometimes trial and error is the best way to figure it out.

Any friction shifting front shifter should work, double or triple doesn't matter, nor should it matter if it's a bar end shifter, stem shifter, downtube shifter, etc.
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Old 02-28-08, 01:54 PM   #14
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When you switch from double to triple, you also need to change bottom brackets. In my experience, the BB spindle for a triple is always longer, about 5 mm. or so. A triple front derailleur will also shift a lot better becuase the profile will match the rings better. You can get a Sora for ~$20.
I already had a 128mm bb on there so ....

I decided that changing the front derailler was the way to go...and funny you should mention the $20 Sora because that is exactly what I found in the old parts bin to put on there. Works like a charm. I had to run a short piece of cable housing under the BB shell because I didn't have a cable guide...thanks to S.B. for that little tip.

thanks guys for all your comments
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