Front derailleur to chainring compatibility?

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

Quoted message said:

Greetings,

I am currently looking to upgrade the front derailleur on my Trek 4300
8spd.

When I look at specs for compatibility with chainrings I have some
questions.

My crankset has 42/34/24 chanirings.

The derailleur specs may list a "top to bottom ring max 22T". My top
to bottom difference is 18T, so this looks fine.

The next spec will list a "top to middle min" of 10T or 12T. I do the
math on my chainrings and I only come up with 8T. Does this mean my
crankset is not compatible with these derailleurs? All the new
derailleurs I have looked at seem to list the same 10T or 12T min. Do
I have some kind of fluky crankset that needs to be upgraded? I don't
want to install a component that works, but is finicky. I want solid
performance.

I assume you have a http://www.trekbikes.com/bikes/2005/mountain/4300.jsp

Just about any Shimano front derailleur made today will work. The
setup will be *slightly* finicky- make sure the derailleur cage
reaches the outer chainring without hitting the middle chainring, but
once it's set up, it'll work perfectly.

BTW: what do you hope to gain by "upgrading"? In my experience,
there's very little functional difference in among the various grades
of front derailleur.

Jeff

[email hidden] (Jeff Wills) wrote in message

Quoted message said:

Quoted message said:

Greetings,

I am currently looking to upgrade the front derailleur on my Trek 4300
8spd.
When I look at specs for compatibility with chainrings I have some
questions.
My crankset has 42/34/24 chanirings.
The derailleur specs may list a "top to bottom ring max 22T". My top
to bottom difference is 18T, so this looks fine.
The next spec will list a "top to middle min" of 10T or 12T. I do the
math on my chainrings and I only come up with 8T. Does this mean my
crankset is not compatible with these derailleurs? All the new
derailleurs I have looked at seem to list the same 10T or 12T min. Do
I have some kind of fluky crankset that needs to be upgraded? I don't
want to install a component that works, but is finicky. I want solid
performance.

I assume you have a http://www.trekbikes.com/bikes/2005/mountain/4300.jsp

Correct

Quoted message said:

Just about any Shimano front derailleur made today will work. The
setup will be *slightly* finicky- make sure the derailleur cage
reaches the outer chainring without hitting the middle chainring, but
once it's set up, it'll work perfectly.
BTW: what do you hope to gain by "upgrading"? In my experience,
there's very little functional difference in among the various grades
of front derailleur.
Jeff

Jeff,

I am pretty pleased with the overall function of the 4300 and its
drivetrain. The rear derailleur is an Alivio and it has functioned
flawlessly. Nothing fancy, but I think it will get the job done. The
front derailleur has been a bit fussy and not crisp. It looks like it
wasn't made to last and appears to be the weakest link on the bike.
The model is a C050 derailleur designed as the entry level derailleur
for a comfort bike. It is not even specd for MTB use. That likely puts
is below acera, altus, and maybe even tourney. I don't beat my bike,
but I do drive in gritty terrain. I just don't think it will hold up.

Also, the body (top swing) lies right in the splash path of my rear
tire. I recently put fenders on to keep the stripe off my back and the
grit off of other components. The rear fender ends just short of the
front derailleur and gets a lot of gunk on it. I am considering
getting a better quality "bottom swing" derailleur. This should allow
me to mount it further up the seat tube, protecting the body of the
front derailleur behind the fender. I can toss the C050 in the parts
bin as an emergency back up (while it still has some life in it).
Besides, decent front derailleurs are relatively inexpensive.
Especially the perceived obsolete 8 spd derailleurs.

I am still trying to understand the "top to mid" min chain ring specs
from shimano. I know that there are many combinations of drivetrain
parts that can be mixed and matched. I also believe that while many of
these arrangements may "function", they can also diminish efficient
performance and may also reduce the lifespan of the component. When I
am able, I try to stay within specs (fewer potential headaches). I
would like to know if I am interpreting that spec correctly.

Cheers, Tracy

Quoted message said:

I am still trying to understand the "top to mid" min chain ring specs
from shimano. I know that there are many combinations of drivetrain
parts that can be mixed and matched. I also believe that while many of
these arrangements may "function", they can also diminish efficient
performance and may also reduce the lifespan of the component. When I
am able, I try to stay within specs (fewer potential headaches). I
would like to know if I am interpreting that spec correctly.

Cheers, Tracy

I went to my LBS and asked this question of one of the techs. His
answer was obvious BS. He had no clue. I think I may have finally
answered my own question by actually using my brain (ouch).

A derailluer cage will have specific dimensions for the outside and
the inside plate. When a derailleur is properly installled, there will
be an optimum clearance between the top of the large chain ring and
the bottom of the outside derailleur plate. If I use a middle
chainring that is 8T different from the large chainring (instead of
the 10 or 12T specd on most 9 speed derailleurs) then the inside plate
of the derailleur cage will hit the middle chainring before allowing a
complete shift to the large chainring. The only fix for this is to
raise the height of the derailleur body to clear the middle chainring.
This in turn makes the derailleur cage to large chainring distance
larger than optimum. This may in turn reduce the reliability and
effectiveness of the shifting.

That's my story and I'm sticking to it.

Cheers, Tracy

In article <[email hidden]>, Pizza Man

Quoted message said:

Quoted message said:

I am still trying to understand the "top to mid" min chain ring specs
from shimano. I know that there are many combinations of drivetrain
parts that can be mixed and matched. I also believe that while many of
these arrangements may "function", they can also diminish efficient
performance and may also reduce the lifespan of the component. When I
am able, I try to stay within specs (fewer potential headaches). I
would like to know if I am interpreting that spec correctly.

Cheers, Tracy

I went to my LBS and asked this question of one of the techs. His
answer was obvious BS. He had no clue. I think I may have finally
answered my own question by actually using my brain (ouch).

A derailluer cage will have specific dimensions for the outside and
the inside plate. When a derailleur is properly installled, there will
be an optimum clearance between the top of the large chain ring and
the bottom of the outside derailleur plate. If I use a middle
chainring that is 8T different from the large chainring (instead of
the 10 or 12T specd on most 9 speed derailleurs) then the inside plate
of the derailleur cage will hit the middle chainring before allowing a
complete shift to the large chainring. The only fix for this is to
raise the height of the derailleur body to clear the middle chainring.
This in turn makes the derailleur cage to large chainring distance
larger than optimum. This may in turn reduce the reliability and
effectiveness of the shifting.

That's my story and I'm sticking to it.

Cheers, Tracy

There is also another consideration pm: The length of the front
derailleur cage. Consider this setup; I'm running a 3 ring FSA Gossamer
crank (chainring sizes are 53,39,30) in conjunction with a Suntour Arx
front derailleur and friction downtube shifter. The Arx was originally
from an Asian Bianchi circa late 80s and is designed for a dual
chainring crankset. I love this derailleur, mainly for sentimental
reasons, and when installing the FSA crankset presumed that the extra
derailleur sweep required would regrettably reconcile the Arx to the
spare parts bin.

But the venerable Suntour accomodated the three chainrings. With
qualifications though. The short cage of the Arx derailleur was not
meant for so small a chainring as 30t. Consequently, when in the granny
ring, the chain rides atop the bolt that secures the inner and outer
derailleur plates together (at the lower end of the cage.) This could
contribute to chain derailments.

If your mix and matching spare parts, cage length vis-a-vis chainring
combinations is a factor when determining an appropriate derailleur.

luke

Luke said:

In article <[email hidden]>, Pizza Man

Quoted message said:

Quoted message said:

I am still trying to understand the "top to mid" min chain ring specs
from shimano. I know that there are many combinations of drivetrain
parts that can be mixed and matched. I also believe that while many of
these arrangements may "function", they can also diminish efficient
performance and may also reduce the lifespan of the component. When I
am able, I try to stay within specs (fewer potential headaches). I
would like to know if I am interpreting that spec correctly.

Cheers, Tracy

I went to my LBS and asked this question of one of the techs. His
answer was obvious BS. He had no clue. I think I may have finally
answered my own question by actually using my brain (ouch).

A derailluer cage will have specific dimensions for the outside and
the inside plate. When a derailleur is properly installled, there will
be an optimum clearance between the top of the large chain ring and
the bottom of the outside derailleur plate. If I use a middle
chainring that is 8T different from the large chainring (instead of
the 10 or 12T specd on most 9 speed derailleurs) then the inside plate
of the derailleur cage will hit the middle chainring before allowing a
complete shift to the large chainring. The only fix for this is to
raise the height of the derailleur body to clear the middle chainring.
This in turn makes the derailleur cage to large chainring distance
larger than optimum. This may in turn reduce the reliability and
effectiveness of the shifting.

That's my story and I'm sticking to it.

Cheers, Tracy

There is also another consideration pm: The length of the front
derailleur cage. Consider this setup; I'm running a 3 ring FSA Gossamer
crank (chainring sizes are 53,39,30) in conjunction with a Suntour Arx
front derailleur and friction downtube shifter. The Arx was originally
from an Asian Bianchi circa late 80s and is designed for a dual
chainring crankset. I love this derailleur, mainly for sentimental
reasons, and when installing the FSA crankset presumed that the extra
derailleur sweep required would regrettably reconcile the Arx to the
spare parts bin.

But the venerable Suntour accomodated the three chainrings. With
qualifications though. The short cage of the Arx derailleur was not
meant for so small a chainring as 30t. Consequently, when in the granny
ring, the chain rides atop the bolt that secures the inner and outer
derailleur plates together (at the lower end of the cage.) This could
contribute to chain derailments.

If your mix and matching spare parts, cage length vis-a-vis chainring
combinations is a factor when determining an appropriate derailleur.

luke

Another problem I've encountered is the bottom of the cage fouling the
wire going to the rear derailleur. This limits how far down I can place
the front derailleur, though it does just work with a bit of jiggling
(44-40-26).

Anthony

--
Using Linux GNU/Debian - Windows-free zone
http://www.acampbell.org.uk (book reviews,
Assassins, homeopathy, and skeptical articles).
Email: replace "www" with "ac@"

Quoted message said:

Quoted message said:

Quoted message said:

Cheers, Tracy

I went to my LBS and asked this question of one of the techs. His
answer was obvious BS. He had no clue. I think I may have finally
answered my own question by actually using my brain (ouch).

A derailluer cage will have specific dimensions for the outside and
the inside plate. When a derailleur is properly installled, there will
be an optimum clearance between the top of the large chain ring and
the bottom of the outside derailleur plate. If I use a middle
chainring that is 8T different from the large chainring (instead of
the 10 or 12T specd on most 9 speed derailleurs) then the inside plate
of the derailleur cage will hit the middle chainring before allowing a
complete shift to the large chainring. The only fix for this is to
raise the height of the derailleur body to clear the middle chainring.
This in turn makes the derailleur cage to large chainring distance
larger than optimum. This may in turn reduce the reliability and
effectiveness of the shifting.

That's my story and I'm sticking to it.

Cheers, Tracy

There is also another consideration pm: The length of the front
derailleur cage. Consider this setup; I'm running a 3 ring FSA Gossamer
crank (chainring sizes are 53,39,30) in conjunction with a Suntour Arx
front derailleur and friction downtube shifter. The Arx was originally
from an Asian Bianchi circa late 80s and is designed for a dual
chainring crankset. I love this derailleur, mainly for sentimental
reasons, and when installing the FSA crankset presumed that the extra
derailleur sweep required would regrettably reconcile the Arx to the
spare parts bin.

But the venerable Suntour accomodated the three chainrings. With
qualifications though. The short cage of the Arx derailleur was not
meant for so small a chainring as 30t. Consequently, when in the granny
ring, the chain rides atop the bolt that secures the inner and outer
derailleur plates together (at the lower end of the cage.) This could
contribute to chain derailments.

If your mix and matching spare parts, cage length vis-a-vis chainring
combinations is a factor when determining an appropriate derailleur.

luke

Luke,

The derailleurs and crankset are both 3 speed so I don't think this is
a consideration here.

However, it is very relavant for other upgrades. I am considering
upgrading my 1980 Centurion touring bike. Like you, I love the old
components on this bike. Unfortunately my current situation makes the
gearing on this bike too high. I have looked at various solutions.
Sheldon Brown's shop (Nice guys) suggested a Triplizer. This replaces
the low gear on my crankset and turns it into a middle ring, with tabs
for a smaller 3rd ring. The 3rd ring would have to be quite small as I
cannot go any lower in the rear freewheel without chainging the rear
hub and getting a suntour wide-range freewheel. I was sure hoping to
keep the ol' Suntour VXs derailleur, but I am pretty sure after your
input, I would have cage length problems. So, new derailleur, new
Triplizer, new 3rd chainring.... More than the bike is worth in $$$.
Maybe just reserve the Centurion for my "level ground" bike.

Thanks for the input. Tracy