Chain rubs on large Chainring when on smaller rear cogs

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

Quoted message said:

Yesterday I thought the chain was rubbing on the derailleur when in
small front small rear combo. I adjusted derailleur and it does not
touch chain. The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. Bike
info. 2001 Cannondale xr800. cannondale expert cranks, 105 sti f&r
derailleurs. Any ideas would be appreciated. Is it an alignment issue?

"Doctor, it hurts when I do this" "Don't do that!"

Avoid extreme gear combinations, i.e. biggest to biggest and smallest
to smallest. They're not meant be used.

-Jens

It depends on the length of the chainstay and the size of the large front
ring.

For example, on a Cervelo frame -- which has a very short chainstay, if you
use the small cog in the rear and the small front chainring, there's an
excellent chance the chain will rub the inside of the large chainring. This
is normal and expected. This is a bad chainline anyway, so it shouldn't be
used. You want to keep the chain as straight as possible, not curved. Chains
work best and last longest when used in a straight line.

Additionally, if you have a very large chainring in the front, it could rub
the chain in the small small combination no matter how long or short the
chainstay. Again, it's best to stay out of that combination. You are putting
undue lateral stress on the chain. This causes added friction and power
loss. Plus you scratch up the inside of the big ring doing that.

AB

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

Quoted message said:

Yesterday I thought the chain was rubbing on the derailleur when in
small front small rear combo. I adjusted derailleur and it does not
touch chain. The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. Bike
info. 2001 Cannondale xr800. cannondale expert cranks, 105 sti f&r
derailleurs. Any ideas would be appreciated. Is it an alignment issue?

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jab-<< The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. >><BR><BR>

No fix necessary, it is NORMAL with yours and just about everyother modern road
setup.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

busterb said:

Yesterday I thought the chain was rubbing on the derailleur when in
small front small rear combo. I adjusted derailleur and it does not
touch chain. The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. Bike
info. 2001 Cannondale xr800. cannondale expert cranks, 105 sti f&r
derailleurs. Any ideas would be appreciated. Is it an alignment issue?

Your subject and body conflict with each other. Which is it?

--
Phil, Squid-in-Training

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

Quoted message said:

busterb said:

Yesterday I thought the chain was rubbing on the derailleur when in
small front small rear combo. I adjusted derailleur and it does not
touch chain. The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. Bike
info. 2001 Cannondale xr800. cannondale expert cranks, 105 sti f&r
derailleurs. Any ideas would be appreciated. Is it an alignment issue?

Your subject and body conflict with each other. Which is it?

Pretty simple to picture: Chain on inner front chainring and smaller
two rear gears. Chain rubs on the large front chainring (double)
making awful racket.
I just wanted to know if shimming something or adding a washer would
correct this as I would like to use these gear combos.

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In article <[email hidden]>,

busterb said:

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

Quoted message said:

busterb said:

Yesterday I thought the chain was rubbing on the derailleur when in
small front small rear combo. I adjusted derailleur and it does not
touch chain. The noiise is due to the chain catching in the big
chainring slightly and rubbing. I know I can bring it to where I
bought it a week ago but if I can fix it Ill save the trip. Bike
info. 2001 Cannondale xr800. cannondale expert cranks, 105 sti f&r
derailleurs. Any ideas would be appreciated. Is it an alignment issue?

Your subject and body conflict with each other. Which is it?

Pretty simple to picture: Chain on inner front chainring and smaller
two rear gears. Chain rubs on the large front chainring (double)
making awful racket.
I just wanted to know if shimming something or adding a washer would
correct this as I would like to use these gear combos.

_ Yes, adding a 0.6 or 1.2mm washers to all the chainring bolts
will fix this problem[1]. Buy at least 10 since they are pretty
easy to crunch while being installed. You should avoid using
those gears if you can as it wears the chain faster and is less
efficient, but the bike is there to serve me, not me to serve
the needs of the bike.

_ Booker C. Bense

[1]- Make sure that you don't end up with chainrings far enough
apart that the chain can jam between them. On bikes with
short chainstays, it may not be possible to use the
small/small gears without creating a much bigger problem.
If you have to choose between small/small with rubbing
and the potential for the chain jamming between the rings
stick with the small/small rubbing.

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booker-<< Yes, adding a 0.6 or 1.2mm washers to all the chainring bolts
will fix this problem[1]. >><BR><BR>

C'mon Booker, It's not a problem to be fixed. By moving the chainring out you
run the risk of [censored] poor front der action or jamming the chain between the
rings. It is like chugging up a hill in a car in fourth gear, just don't do
that. You wouldn't have your tranny taken apart and changed on your car would
you?

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

-----BEGIN PGP SIGNED MESSAGE-----

In article <[email hidden]>,

Qui si parla Campagnolo said:

booker-<< Yes, adding a 0.6 or 1.2mm washers to all the chainring bolts
will fix this problem[1]. >><BR><BR>

C'mon Booker, It's not a problem to be fixed. By moving the chainring out you
run the risk of [censored] poor front der action or jamming the chain between the
rings. It is like chugging up a hill in a car in fourth gear, just don't do
that. You wouldn't have your tranny taken apart and changed on your car would
you?

_ I told him how he could fix it and the potential problems. I
figured there was enough other advise in the thread about why
fixing it was a bad idea that he could make his own choices. I
think it's the difference in perspective between a bike shop
owner and a shade tree bike mechanic. You're legally responsible
for your work, I'm just a random geek on the internet with lot's
of bad advice.

_ Booker C. Bense

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Booker-<< I
think it's the difference in perspective between a bike shop
owner and a shade tree bike mechanic. You're legally responsible
for your work, I'm just a random geek on the internet with lot's
of bad advice. >><BR><BR>

Perhaps but fixing a problem that doesn't exist should be the same for both.

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

-----BEGIN PGP SIGNED MESSAGE-----

In article <[email hidden]>,

Qui si parla Campagnolo said:

Booker-<< I
think it's the difference in perspective between a bike shop
owner and a shade tree bike mechanic. You're legally responsible
for your work, I'm just a random geek on the internet with lot's
of bad advice. >><BR><BR>

Perhaps but fixing a problem that doesn't exist should be the same for both.

_ I'm not convinced it isn't a problem. This question inspired me
to look at my bikes and I can't see why small/small is inherently
bad or not any worse that a lot of other gears I use all the
time. It's certainly bad if the chainstays are short enough that
the chain rubs on the big ring or if you don't have enough chain
wrap in the derailler. But, I don't get the chainline
arguement. On all my bikes either the middle of a triple or inner
of a double lines up with the middle ring of a 9 speed
rear cluster. So the chainline is the same[1] for the
small/small as the small/big. Certainly you wouldn't tell people
not to use their low gear because of bad chainline. Perhaps,
there's a similar gear on the big ring with a better chainline,
but if you have a wide range double the same gear on the big ring
actually has a worse chainline and on my triples it's roughly the
same. Small/small is a fairly useful gear on a wide range double
at least for short bits.

_ How much chainline angle is "bad"? Where is the line between
acceptable and not? What am I missing? I mean what's the point
of 9 or 10 speed clusters if you actually don't get any more useable
gears than you would with a 7 speed cluster?

_ While you may not think it's a problem, I would certainly think
twice about buying a bike in which I couldn't shift into all the
gears on a test ride. Real or not, it's your customers that
decide what's a problem and what isn't.

_ Booker C. Bense

[1]- Actually it might even be slightly better since there is
a slightly longer distance due to the smaller ring.

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Booker-<< It's certainly bad if the chainstays are short enough that
the chain rubs on the big ring or if you don't have enough chain
wrap in the derailler. But, I don't get the chainline
arguement. >><BR><BR>

The 'argument' is that severe cross chaining wears stuff out quickly, even thoi
a similar gear ratio is available by getting off the small ring to the big one
and shifting up the cogset a few.

Booker<< Small/small is a fairly useful gear on a wide range double
at least for short bits. >><BR><BR>

Ya got this easy, shifters at your finger tips, automatic shifting system, why
not just use it and preserve your equipment?

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

Quoted message said:

Ya got this easy, shifters at your finger tips, automatic shifting
system, why not just use it and preserve your equipment?

It's likely that Booker skids his/her rear tire at every stop, just because
he/she can.

The fact that tire life would be measured in the single digits of miles
doesn't really matter, because it would still be useful in stopping the
bike/rider.

--
Phil, Squid-in-Training

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In article <[email hidden]>,

Qui si parla Campagnolo said:

Booker-<< It's certainly bad if the chainstays are short enough that
the chain rubs on the big ring or if you don't have enough chain
wrap in the derailler. But, I don't get the chainline
arguement. >><BR><BR>

The 'argument' is that severe cross chaining wears stuff out quickly, even thoi
a similar gear ratio is available by getting off the small ring to the big one
and shifting up the cogset a few.

_ But, the chainline is just as bad if not worse for the same
gear ratio using the big ring on a wide range double. IMHO, this
is the tricky part of selecting gears for a wide range double,
there's a gap where you have accept bad crosschaining or a big
jump in gears. That gap needs to occur at a speed you don't use
very often.

Quoted message said:

Booker<< Small/small is a fairly useful gear on a wide range double
at least for short bits. >><BR><BR>

Ya got this easy, shifters at your finger tips, automatic shifting system, why
not just use it and preserve your equipment?

_ I have downtube shifters actually and this weird inclination
for rational proof and real measurements, rather than bike shop
folklore. Since you didn't bother to actually read my post and
answer the question, I don't see much point in further
discussion.

_ Booker C. Bense

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booker-<< I have downtube shifters actually and this weird inclination
for rational proof and real measurements, rather than bike shop
folklore >><BR><BR>

Adios muchacho-

Peter Chisholm
Vecchio's Bicicletteria
1833 Pearl St.
Boulder, CO, 80302
(303)440-3535
http://www.vecchios.com
"Ruote convenzionali costruite eccezionalmente bene"

Booker C. Bense said:

Quoted message said:

The 'argument' is that severe cross chaining wears stuff out quickly, even thoi
a similar gear ratio is available by getting off the small ring to the big one
and shifting up the cogset a few.

Quoted message said:

_ But, the chainline is just as bad if not worse for the same
gear ratio using the big ring on a wide range double. IMHO, this
is the tricky part of selecting gears for a wide range double,
there's a gap where you have accept bad crosschaining or a big
jump in gears. That gap needs to occur at a speed you don't use
very often.

Small cogs wear out faster than large cogs if used the same
amount.

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In article <[email hidden]>,

Qui si parla Campagnolo said:

booker-<< I have downtube shifters actually and this weird inclination
for rational proof and real measurements, rather than bike shop
folklore >><BR><BR>

_ I got curious and it turns out somebody has done the science
at least once recently.

http://www.jhu.edu/news_info/news/home99/aug99/bike.html

_ Apparently, the range is roughly 81 to 98 % efficiency
and big sprockets under high tension are more efficient.
I would really like to see the graph of chainline angle
vs effieciency...

_ Booker C. Bense

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Quoted message said:

_ I got curious and it turns out somebody has done the science
at least once recently.

http://www.jhu.edu/news_info/news/home99/aug99/bike.html

_ Apparently, the range is roughly 81 to 98 % efficiency
and big sprockets under high tension are more efficient.
I would really like to see the graph of chainline angle
vs effieciency...

Interesting article but they did not test lateral angles. And they
said two things somewhat at conflict as smaller chainrings increase
tension (increasing efficiency) and large chainrings reduce chain
friction (increasing efficiency).

On 18 Jun 2004 14:06:17 -0700, [email hidden]

(velodancer) said:

Quoted message said:

_ I got curious and it turns out somebody has done the science
at least once recently.

http://www.jhu.edu/news_info/news/home99/aug99/bike.html

_ Apparently, the range is roughly 81 to 98 % efficiency
and big sprockets under high tension are more efficient.
I would really like to see the graph of chainline angle
vs effieciency...

Interesting article but they did not test lateral angles. And they
said two things somewhat at conflict as smaller chainrings increase
tension (increasing efficiency) and large chainrings reduce chain
friction (increasing efficiency).

Dear Velo,

I'm not following you.

The article doesn't seem to say that smaller chainrings
increase tension, so I'm guessing (but possibly wrong) that
this is you, not the article.

On a derailleur system, doesn't tension increase when the
chain moves to the larger sprockets? That is, if I shift on
the front from the small to the large chain-ring, doesn't
chain tension increase?

When I read the article, it seemed to say that large chain
rings reduce friction (the links bend at a smaller angle)
and that greater tension also helps (nothing said about
which sprockets have greater tension on a typical derailleur
system, but my notion is that shifting to larger sprockets
increases tension).

Am I missing your point completely?

Carl Fogel

Carl Fogel said:

On a derailleur system, doesn't tension increase when the
chain moves to the larger sprockets? That is, if I shift on
the front from the small to the large chain-ring, doesn't
chain tension increase?

No, chain tension is higher on a smaller front chainring. Consider
the mechanical advantage created by the difference between crank
length and chainring radius. When the crank is at the 3:00 position:

Chain tension = pedal force * crank length / chainring radius

An example: With a 175mm crank and a 22-tooth chainring, the
mechanical advantage is about 4:1. A 120lb push on the pedal
produces a 480 lb. tension in the chain.

Hope that helps.
--
terry morse Palo Alto, CA http://bike.terrymorse.com/