MTB Single Chainring Chainline problem...

JimBob' email hidden in said:

I'd like to run a single 42T chainring on my MTB (winter hack).

Problem is that when I try and fit the ring in the middle position it hits the chainstay.

Would I be able to leave it in the outer position and maybe use a slightly shorter BB to improve
the chainline (but ensuring that it still clears the chainstay)?

In that case why not stick to middle position and use a *longer* bottom bracket?

--
"Netiquette" states that a signature should be no more than four lines long.

JimBob said:

I'd like to run a single 42T chainring on my MTB (winter hack).

Problem is that when I try and fit the ring in the middle position it hits the chainstay.

Would I be able to leave it in the outer position and maybe use a slightly shorter BB to improve
the chainline (but ensuring that it still clears the chainstay)?

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the rear, it
generates a "wave" in the chain that travels forward, and can often cause the chain to fall off if
there isn't a front derailer or some other device present to prevent this.

That's why this sort of rig isn't more popular

Sheldon "Chainline" Brown +------------------------------------------------------------------+
| Honestly, I think we should just trust our president in every | decision that he makes and we
| should just support that. | -- Britney Spears, September 4, 2003 |
+------------------------------------------------------------------+ Harris Cyclery, West Newton,
Massachusetts Phone 617-244-9772 FAX 617-244-1041 harriscyclery.comharriscyclery.comOpen ↗ Hard-to-find parts
shipped Worldwide captainbike.comcaptainbike.comOpen ↗ sheldonbrown.comsheldonbrown.comOpen ↗

Sheldon Brown <[email hidden]> wrote in message
news:<[email hidden]>... [snip]

Quoted message said:

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the rear,
it generates a "wave" in the chain that travels forward, and can often cause the chain to fall off
if there isn't a front derailer or some other device present to prevent this.

That's why this sort of rig isn't more popular

Sheldon "Chainline" Brown

[snip]

Dear Sheldon,

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn never
threw the chain off its single front chainwheel.

Were its ancient gears or chain different than modern ones?

Was there "some other device" that restrained the chain? (I have a vague notion of some kind of
front-gear guard, but can't remember if it was a shiny round metal strip riveted to the outside of
the chain-ring or a rigid housing mounted on the frame and painted a handsome blue.)

Or was it just that schoolboys never shifted under much of a load or pedalled fast enough to rouse
the chain?

Carl Fogel

Sheldon Brown <[email hidden]> wrote in message news:<[email hidden]>...

Quoted message said:

JimBob said:

I'd like to run a single 42T chainring on my MTB (winter hack).

Problem is that when I try and fit the ring in the middle position it hits the chainstay.

Would I be able to leave it in the outer position and maybe use a slightly shorter BB to improve
the chainline (but ensuring that it still clears the chainstay)?

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the rear,
it generates a "wave" in the chain that travels forward, and can often cause the chain

Quoted message said:

to fall off if there isn't a front derailer or some other device present to prevent this.

Ahh, that explains it. When my front mech gets stubbon and won't budge, shifting up or down one at
the rear is usually enough to get it to shift; must be the "wave effect". That sounds cool.

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

Quoted message said:

JimBob wrote: Yes, but you should be aware that using a rear derailer with no front derailer,
there's a very considerable risk of accidentally throwing the chain off the chainwheel. When you
shift the rear, it generates a "wave" in the chain that travels forward, and can often cause the
chain to fall off if there isn't a front derailer or some other device present to prevent this.

I had this problem when going to a single chainring on my 'cross bike (chain always came off on the
outside). Installing a Spot chainring guard cured it.

Jim Johnson

Carl Fogel said:

Dear Sheldon,

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn never
threw the chain off its single front chainwheel.

Were its ancient gears or chain different than modern ones?

Yes and yes. 5-speed blocks are narrower than 7/8/9-speeds and modern chains are narrower. I don't
know if these make any difference to the "ripple" effect but the more extreme chain angles might
make it all more risky. Also luck plays a part ...Not that there is such thing as luck, really, but
factors like chainline, chain stay length and the way you pedalled and changed gear all affect
likelyhood of mishap.

I once used a single chainset with a 6sp block and the chain would occasionally come off.

Quoted message said:

Was there "some other device" that restrained the chain? (I have a vague notion of some kind of
front-gear guard,

There are various devices to do the job.

~PB

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

Quoted message said:

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn never
threw the chain off its single front chainwheel.

Well I have a 5 speed Hero ATB purchased in India. It has nothing to hold the chain on the chaining
and has only the slightest propensity to throw the chain while riding. However, stop when in the
higher gears -- or back pedal -- and the chain will regularly part company with the chain ring.

This is a fairly new phenomena -- caused, in part, I think, by a general build up of claggy [censored] on
the rear derailleur and freewheel which means these are quite sticky so don't tension the chain
sufficiently. Cleaning helps but doesn't solve the problem.

T

Quoted message said:

Sheldon Brown <[email hidden]> wrote in message
news:<[email hidden]>... [snip]

Quoted message said:

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the rear,
it generates a "wave" in the chain that travels forward, and can often cause the chain to fall off
if there isn't a front derailer or some other device present to prevent this.

That's why this sort of rig isn't more popular

Sheldon "Chainline" Brown

Carl Fogel said:

Dear Sheldon,

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn never
threw the chain off its single front chainwheel.

Were its ancient gears or chain different than modern ones?

Was there "some other device" that restrained the chain? (I have a vague notion of some kind of
front-gear guard, but can't remember if it was a shiny round metal strip riveted to the outside of
the chain-ring or a rigid housing mounted on the frame and painted a handsome blue.)

Or was it just that schoolboys never shifted under much of a load or pedalled fast enough to rouse
the chain?

Yours may have been well-behaved, but, in that era, a dropped chain was a common complaint. Drove
mechanics nuts, as there wasn't a sure adjustment or modifictaion to guarantee it wouldn't recur.

And it didn't help that the typical 5-speed Sprite or Suburban customer was much less technically
inclined than the "ten speed " crowd. Much more likely to stand in the doorway, chain askew, and
complain "the bike you sold me doesn't work".

That memory lingers.

--
Andrew Muzi www.yellowjersey.org Open every day since 1 April, 1971

Pete Biggs <[email hidden]> wrote ...

Quoted message said:

Carl Fogel said:

Dear Sheldon,

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn never
threw the chain off its single front chainwheel.

Were its ancient gears or chain different than modern ones?

Yes and yes. 5-speed blocks are narrower than 7/8/9-speeds and modern chains are narrower. I don't
know if these make any difference to the "ripple" effect but the more extreme chain angles might
make it all more risky. Also luck plays a part ...Not that there is such thing as luck, really,
but factors like chainline, chain stay length and the way you pedalled and changed gear all affect
likelyhood of mishap.

I once used a single chainset with a 6sp block and the chain would occasionally come off.

Also old-style chainrings had proper teeth - none of the half chopped-off easy-shift teeth that you
get now, specially designed to help the chain come off the chainring.

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

Quoted message said:

Sheldon Brown <[email hidden]> wrote in message
news:<[email hidden]>... [snip]

Quoted message said:

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the
rear, it generates a "wave" in the chain that travels forward, and can often cause the chain to
fall off if there isn't a front derailer or some other device present to prevent this.

That's why this sort of rig isn't more popular

Sheldon "Chainline" Brown

[snip]

My faith in Sheldon was quickly rewarded.

In an unrelated post, CT described his chain coming off his 8-speed folder bike with a single front
chain-ring "more than I'd like."

Hard luck for CT, but perfect support for Sheldon's explanation. The short chain stay presumably
increases the chain angle and helps the chain fall off.

Carl Fogel

Quoted message said:

Quoted message said:

Subject: Re: Folders, 8 speed cassettes, etc.

"CT" <[email hidden]> wrote in message
"]news:[email hidden]... Hi all

I have a folder for commuting that currently has an 8-speed 11-28 cassette and 52 chain ring. The
chain tends to skip off more than I'd like (I've been told the short chain stay makes things
worse . . .

Quoted message said:

Quoted message said:

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the
rear, it generates a "wave" in the chain that travels forward, and can often cause the chain to
fall off if there isn't a front derailer or some other device present to prevent this.

It even happens to the best Pros !

In the 6.5 KM time trial prologue of this years Tour De France David Millar was leading by 5 seconds
with less than 1 km to go when his chain popped of his 55 tooth front chainring. Millar didn't have
a front derailleur on his bike - a stage lost for the sake of 100 grams
!

See cyclingnews.comtour.phpOpen ↗

Rik O'Shea said:

Quoted message said:

Quoted message said:

Yes, but you should be aware that using a rear derailer with no front derailer, there's a very
considerable risk of accidentally throwing the chain off the chainwheel. When you shift the
rear, it generates a "wave" in the chain that travels forward, and can often cause the chain
to fall off if there isn't a front derailer or some other device present to prevent this.

Quoted message said:

It even happens to the best Pros !

Well, I beg to differ here. Granted that, if the derailer is there, it does help keep the
chain engaged if it tries to jump off for some reason, the real question is: 'How often does
that happen?'.

I bet not so often so that we should spend time telling its virtues.

A stingy friend of mine rides a triple without derailer (he did not want to endure the expense of
buying a long-arm derailer for his bike). At the foot of the hill he dismounts and shifts by hand,
and reverses the set up, again by hand, before starting the descent.

No trouble whatsoever with chain falling off, ever, as he confirmed to me the other day. But, of
course, he is not a professional cyclist, by all means.

Sergio Pisa

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Rik O'Shea said:

Quoted message said:

> Yes, but you should be aware that using a rear derailer with no front derailer, there's a
> very considerable risk of accidentally throwing the chain off the chainwheel. When you shift
> the rear, it generates a "wave" in the chain that travels forward, and can often cause the
> chain to fall off if there isn't a front derailer or some other device present to prevent
> this.

Quoted message said:

It even happens to the best Pros !

Well, I beg to differ here.

I have to side with the guru on this one (is he ever wrong). My sons mtb displayed a tendency to
throw its chain while running with no front changer while I waited for a replacement to arrive in
the post. cheers Iain C

iarocu said:

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Well, I beg to differ here.

I have to side with the guru on this one (is he ever wrong). My sons mtb displayed a tendency to
throw its chain while running with no front changer while I waited for a replacement to arrive in
the post. cheers Iain C

Not my intention to dispute your experience, nor the Guru's for that matter, but I am really curious
as to how frequent such tendency is. And, of course, with what equipment.

Beside's my friend's happiness with the no-front-changer configuration, let me say that in none of
my (very old) bikes I have noticed the changer has ever fullfilled any such role.

Well, so much for that.

Sergio Pisa

Andrew Sweetman said:

Pete Biggs said:

Carl Fogel said:

I believe you, but I'm trying to figure out why my long-vanished 5-speed pre-1970 Schwinn
never threw the chain off its single front chainwheel.

Were its ancient gears or chain different than modern ones?

Yes and yes. 5-speed blocks are narrower than 7/8/9-speeds and modern chains are narrower.

Also old-style chainrings had proper teeth - none of the half chopped-off easy-shift teeth that
you get now, specially designed to help the chain come off the chainring.

Also worth noting is that modern MTB chainstays are some 1.5" shorter than those of vintage
recreational bikes.

Chalo Colina

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

iarocu said:

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Well, I beg to differ here.

I have to side with the guru on this one (is he ever wrong). My sons mtb displayed a tendency to
throw its chain while running with no front changer while I waited for a replacement to arrive
in the post. cheers Iain C

Not my intention to dispute your experience, nor the Guru's for that matter, but I am really
curious as to how frequent such tendency is. And, of course, with what equipment.

Beside's my friend's happiness with the no-front-changer configuration, let me say that in none of
my (very old) bikes I have noticed the changer has ever fullfilled any such role.

Well, so much for that.

Sergio Pisa

Dear Sergio,

Perhaps several factors combine to make the chain more or less secure on a single unguarded front
chain-ring?

Sheldon Brown has pointed out elsewhere that the shorter the chain-stay, the more likely the chain
is to come off, presumably because the angle is greater.

Other posters have pointed out that gear teeth have changed and become less likely to retain
the chain.

Embarrassingly, I never lost a chain off my no-derailleur 5-speed in the 1970's, but my chain has
come off my current 53-tooth on a few occasions not when I was shifting or even pedalling, but when
I was coasting tucked-in down a long daily stretch of paved road with a heavy side-wind and hit what
seemed like a minor bump. (I have trouble believing that the wind mattered, but the chain did go off
in the wind's direction every time.) I suspect that my front derailleur, meant for a triple but now
used on a double, allows more chain movement than is common in polite society.

Combine bumps, short chain stays, lower-profile teeth, and the shifting ripple that Sheldon
describes, and some people are likely to be startled by chains falling off the front gear, while
people with longer chain-stays, gears not quite as worn, smoother roads, and better maintenance are
left wondering what the fuss is about.

Carl Fogel

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

iarocu said:

Sergio SERVADIO <[email hidden]> wrote in message
news:<[email hidden]>...

Quoted message said:

Well, I beg to differ here.

I have to side with the guru on this one (is he ever wrong). My sons mtb displayed a tendency to
throw its chain while running with no front changer while I waited for a replacement to arrive
in the post. cheers Iain C

Not my intention to dispute your experience, nor the Guru's for that matter, but I am really
curious as to how frequent such tendency is. And, of course, with what equipment.

Beside's my friend's happiness with the no-front-changer configuration, let me say that in none of
my (very old) bikes I have noticed the changer has ever fullfilled any such role.

In the seventies some of my friends had 5 speed bikes with a single

front chainring and 5 speed block at the back. They did not have problems. Sheldons explanation (or
theory?) I would expect relates to modern triple chainrings which allow easy front shifting and may
not affect single front rings with "proper" teeth. I have not heard of anyone having problems with
the Edinburgh Courier single chainring city bike. I presume it also has a different style chainring
to the Shimano triple rings with their ramps etc. cheers Iain C