Why doesn't this chainline work?

Mike said:

I've been building up a late-90s Trek 5200. Trek confirms there was a
triple option for this bike when it was new, but I'm having trouble
making it work. I'm using an 8sp 105 triple crank, 113mm BB, Ultegra
triple FD, and 9sp cassette. When the chain is in the middle of the
cassette and the middle ring, it looks good and straight, but by the
time it's on the second-largest or second-smallest cog - still on the
middle ring - it is so angled it won't work.

What does "not work" mean here? Does it just mean that your chain rubs on
the derailleur carriage, or that it rubs on the big ring (in the
smaller sprockets)?

Quoted message said:

That suggests the
cassette is too wide, and I realize it was probably an 8sp originally,
but isn't an 8sp cassette the same width as a 9sp?

8sp, 9sp, 10sp, same width.

Given how angled the

Quoted message said:

chain becomes just on the middle ring, I don't see how this could even
work with a double (assuming the big ring would be about where the
middle ring is now).

Well, wasn't there something on the bike before?

Frankly, I can't see any real problem in getting this to work just fine.
You haven't really explained what is wrong about it.

Quoted message said:

Other information: Trek says the original triple option had a 115mm BB.
While adding 1mm may (or may not) improve shifting to the highest cogs,
it will worsen shifting to the lowest.

1mm, one smillimeter. Not important.

--

David L. Johnson

__o | Some people used to claim that, if enough monkeys sat in front
_`\(,_ | of enough typewriters and typed long enough, eventually one of
(_)/ (_) | them would reproduce the collected works of Shakespeare. The
internet has proven this not to be the case.

"David L. Johnson" <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

Mike said:

I've been building up a late-90s Trek 5200. Trek confirms there was a
triple option for this bike when it was new, but I'm having trouble
making it work. I'm using an 8sp 105 triple crank, 113mm BB, Ultegra
triple FD, and 9sp cassette. When the chain is in the middle of the
cassette and the middle ring, it looks good and straight, but by the
time it's on the second-largest or second-smallest cog - still on the
middle ring - it is so angled it won't work.

What does "not work" mean here? Does it just mean that your chain rubs on
the derailleur carriage, or that it rubs on the big ring (in the
smaller sprockets)?

Sorry, here's more detail: Chain won't stay on the middle ring when
shifted to the second-largest or largest cogs because it is so angled.
And yet, no amount of FD adjustment or shifter trim will keep the
chain from rubbing on the derailer cage in the other direction, when
shifted to the second-smallest or smallest cogs, because the chain is
so angled in the other direction. In each of the three rings there are
only about 3 cogs where the chainline is straight enough to avoid
contact with one side or the other of the inside of the FD cage.

Mike

Please be advised that that not every possible
combination of chainring/cassette gearing is to be
expected to be functional. The smallest and
middle chainring should work with the biggest
gears on the cassette. The largest chainring
should work with the smaller gears on the
cassette. Unless you are using a 36 tooth on the
cassette as a low, more range for the middle
chainring is to be expected.

If it don't work, it may be time for a new chain,
or to lubricate the old one.

"Mike" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

I've been building up a late-90s Trek 5200. Trek

confirms there was a

Quoted message said:

triple option for this bike when it was new, but

I'm having trouble

Quoted message said:

making it work. I'm using an 8sp 105 triple

crank, 113mm BB, Ultegra

Quoted message said:

triple FD, and 9sp cassette. When the chain is

in the middle of the

Quoted message said:

cassette and the middle ring, it looks good and

straight, but by the

Quoted message said:

time it's on the second-largest or

second-smallest cog - still on the

Quoted message said:

middle ring - it is so angled it won't work.

That suggests the

Quoted message said:

cassette is too wide, and I realize it was

probably an 8sp originally,

Quoted message said:

but isn't an 8sp cassette the same width as a

9sp? Given how angled

Quoted message said:

the chain becomes just on the middle ring, I

don't see how this could

Quoted message said:

even work with a double (assuming the big ring

would be about where

Quoted message said:

the middle ring is now).

What's going on? How to fix it? I'd like to keep

it a triple, if

Quoted message said:

possible; if not, I'd like to use a 110bcd crank

and a 50x34.

Quoted message said:

Other information: Trek says the original triple

option had a 115mm

Quoted message said:

BB. While adding 1mm may (or may not) improve

shifting to the highest

Quoted message said:

cogs, it will worsen shifting to the lowest.

Thanks for any advice...

Mike

Mike said:

Quoted message said:

Quoted message said:

I've been building up a late-90s Trek 5200. Trek confirms
there was a triple option for this bike when it was new, but
I'm having trouble making it work. I'm using an 8sp 105 triple
crank, 113mm BB, Ultegra triple FD, and 9sp cassette.
When the chain is in the middle of the cassette and the middle
ring, it looks good and straight, but by the time it's on the
second-largest or second-smallest cog - still on the middle
ring - it is so angled it won't work.

David L. Johnson said:

Quoted message said:

What does "not work" mean here? Does it just mean that your
chain rubs on the derailleur carriage, or that it rubs on the big
ring (in the smaller sprockets)?

Mike <[email hidden]> follows up:

Quoted message said:

Sorry, here's more detail: Chain won't stay on the middle ring when
shifted to the second-largest or largest cogs because it is so angled.
And yet, no amount of FD adjustment or shifter trim will keep the
chain from rubbing on the derailer cage in the other direction, when
shifted to the second-smallest or smallest cogs, because the chain is
so angled in the other direction. In each of the three rings there are
only about 3 cogs where the chainline is straight enough to avoid
contact with one side or the other of the inside of the FD cage.

Are you using a 9-speed chain? The narrow chain width might make an
improvement here.

Quoted message said:

Quoted message said:

Quoted message said:

That suggests the cassette is too wide, and I realize it was
probably an 8sp originally, but isn't an 8sp cassette the same
width as a 9sp?

Quoted message said:

Quoted message said:

8sp, 9sp, 10sp, same width.

Quoted message said:

Quoted message said:

Quoted message said:

Given how angled the chain becomes just on the middle ring, I
don't see how this could even work with a double (assuming
the big ring would be about where the middle ring is now).

Quoted message said:

Quoted message said:

Well, wasn't there something on the bike before?

Quoted message said:

Quoted message said:

Frankly, I can't see any real problem in getting this to work just
fine. You haven't really explained what is wrong about it.

Quoted message said:

Quoted message said:

Quoted message said:

Other information: Trek says the original triple option had a
115mm BB. While adding 1mm may (or may not) improve
shifting to the highest cogs, it will worsen shifting to the lowest.

Quoted message said:

Quoted message said:

1mm, one smillimeter. Not important

"Dale Benjamin" <[email hidden]> wrote in message
news:[email hidden]...

Quoted message said:

Please be advised that that not every possible
combination of chainring/cassette gearing is to be
expected to be functional. The smallest and
middle chainring should work with the biggest
gears on the cassette. The largest chainring
should work with the smaller gears on the
cassette.

Every combination works on my bike (triple with 8-sp Ultegra).

Most of mine do also, 13 - 26 freewheel and 28,
40, 52 chainrings. I can use the 20, 23, 26 in
back with the 28 in front, can go a bit smaller in
the back but don't have quite enough windup on the
back deraileur to go all the way up, I'm subject
to be not real smooth sometimes.

Some chains just get stiff for whatever reason,
then must be replaced. Can't clean and relube in
under 2 hours, so I go for the new chain.

"Peter Cole"
<[email hidden]> wrote in
message news:Ql2Yc.84551$mD.68732@attbi_s02...

Quoted message said:

"Dale Benjamin" <[email hidden]> wrote in

message

Quoted message said:

news:[email hidden]...

Quoted message said:

Please be advised that that not every possible
combination of chainring/cassette gearing is

to be

Quoted message said:

Quoted message said:

expected to be functional. The smallest and
middle chainring should work with the biggest
gears on the cassette. The largest chainring
should work with the smaller gears on the
cassette.

Every combination works on my bike (triple with

8-sp Ultegra).

Quoted message said:

Could it be that your BB is too short? Current model 105 triples use
a 118.5mm BB. I don't know if the older 8sp versions used a shorter
bb, but it is worth checking out.

[email hidden] (Mike) wrote in message news:<[email hidden]>...

Quoted message said:

I've been building up a late-90s Trek 5200. Trek confirms there was a
triple option for this bike when it was new, but I'm having trouble
making it work. (snip)

Thanks for the suggestions. It seems the culprit was FSA rings on the
105 cranks. When I replaced them with the original 105 rings all
combinations work.

Mike