Chainring Orientation

asqui wrote: others have answered most of the rest of your questions... ...

Quoted message said:

What orientation do I want these special teeth in, in relation to the cranks? 0 and 180 degrees
offset from the cranks so that they appear at the top of the chainring when the cranks are at 6/12
o'clock with minimal force being applied?

The cogs should have a tab sticking down in one of the cut-outs. This tab should be aligned with the
crank arm (Shimano). Others may be the same or may be marked in another way. It _does_ make a
difference in shifting.

Quoted message said:

Another chainring question: There appears to be at least a few mm of lateral wobble in the big and
middle chainrings, visible when I spin the cranks quickly and focus on the chainrings against the
background. Is this normal? Can anything be done to corret it? I believe it was like this when I
bought the bike and the LBS didn't seem to think too much of it when I pointed it out.

Mine don't have this. I'd take a look at Sheldon's site (as others have suggested). Bottom line
is: do they shift reliably or ghost shift under power. If they shift reliably, I'd leave it be
for now 🙂.

David

Werehatrack said:

asqui' may have said:

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

If you had three chain rings, there would be some on the middle one as well.

I do have three (though I failed to make this clear), and this is not the case (!)

Quoted message said:

Quoted message said:

Another chainring question: There appears to be at least a few mm of lateral wobble in the big
and middle chainrings, visible when I spin the cranks quickly and focus on the chainrings against
the background. Is this normal? Can anything be done to corret it? I believe it was like this
when I bought the bike and the LBS didn't seem to think too much of it when I pointed it out.

The importance of this may be minimal; if you have no problem with the chain doing unwanted things
under hard pedalling, it's likely that it can be safely ignored. If you have a torque wrench, you
might check the tightness of the crank arm retaining bolt or nut.

What if the chain rubs the derailler under hard pedalling?

Dani

asqui said:

Sorry, I forgot to make it clear that I have a skanky touring bike with a triple chainring,
so really my question is doesn't the same thing apply for when you are changing from granny
to middle.

Maybe, but there's less tension on the chain then, so maybe that's why it's not as important. Now
I'm just grasping at straws! 😉

Quoted message said:

Quoted message said:

Probably not a concern; there may be some offset related to something else that matters, though.

What do you mean?

I just mean that I don't see that it would matter much how they line up with the crank arms, but
maybe they have to line up with something else (I'd bet there's a mark on the middle ring or
some such).

Quoted message said:

Quoted message said:

Read this: sheldonbrown.comstraighten chw.htmlOpen ↗

Damn! And I thought I had read everything there was to read on that site!

That link was really the only very useful information _I_ had for you in the reply. 🙂

Quoted message said:

Thanks for your help.

Quoted message said:

Quoted message said:

Dani

--
Rick Onanian

asqui' may have said:

Werehatrack said:

asqui' may have said:

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

If you had three chain rings, there would be some on the middle one as well.

I do have three (though I failed to make this clear), and this is not the case (!)

It's not unknown, although even my cheap bikes have trimmed teeth on the center wheel. If you're not
having any shifting issues into or out of that cog, don't worry about it.

Quoted message said:

What if the chain rubs the derailler under hard pedalling?

That's what fine-tuning the der adjustment is for. If you're not familiar with the task, the good
hints are here:

sheldonbrown.comderailer adjustment.htmlOpen ↗

If it's rubbing while pedalling hard but not while it's unloaded, and you can't get it under control
with der adjustments, then definitely check for a loose crank retainer bolt or nut just as a safety
matter; if that's not up to spec, you could trash the crank arm. On a couple of occasions, I've run
across setups where I was never able to get the damthing to stop rubbing in some particular gear
combination or condition, but most of the bikes I deal with are, for lack of a less diplomatic
description, crummy. Yours should be able to work without rubbing.

--
My email address is antispammed; pull WEEDS if replying via e-mail. Yes, I have a killfile. If I
don't respond to something, it's also possible that I'm busy.

After soaking my chain in White Spirit and getting it squeaky clean I got to work on cleaning the
grimy sprockets and chainrings. Only after I had removed the chainring did I realise that these
days chainrings are not rotationally symmetrical -- I assume the two adjacent teeth that appear
as if they have been cut short are there to allow the chain to move in and engage the chainring
more easily.

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

Why only on the big chainring? Is it because that is where the derailer is going to be at it's limit
and therefore less effective at forcing it onto the ring?

What orientation do I want these special teeth in, in relation to the cranks? 0 and 180 degrees
offset from the cranks so that they appear at the top of the chainring when the cranks are at 6/12
o'clock with minimal force being applied?

Another chainring question: There appears to be at least a few mm of lateral wobble in the big and
middle chainrings, visible when I spin the cranks quickly and focus on the chainrings against the
background. Is this normal? Can anything be done to corret it? I believe it was like this when I
bought the bike and the LBS didn't seem to think too much of it when I pointed it out.

Dani

asqui said:

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

Why only on the big chainring? Is it because that is where the derailer going to be at it's limit
and therefore less effective at forcing it onto the ring?

Imagine shifting from big ring to small: Chain falls off big ring, lands on smal..

Now imagine shifting from small to big: Chain must climb to big ring.

The chain could use a little help, so the gaps created by the smaller teeth result in some grabby
action on the chain.

Disclaimer: I am not an engineer, mechanic, lawyer, or police officer. I could be wrong.

Quoted message said:

What orientation do I want these special teeth in, in relation to the cranks? 0 and 180 degrees
offset from the cranks so that they appear at top of the chainring when the cranks are at 6/12
o'clock with minimal being applied?

Probably not a concern; there may be some offset related to something else that matters, though.

Quoted message said:

Another chainring question: There appears to be at least a few mm of wobble in the big and middle
chainrings, visible when I spin the cranks quickly and focus on the chainrings against the
background. Is this normal?

Yes, it's normal in so far as lots of people probably never even notice, let alone repair it.

Quoted message said:

Can anything be done to corret it? I believe it was like this when I bought the bike and the LBS
didn't seem to think too much of it when I pointed it out.

Read this: sheldonbrown.comstraighten chw.htmlOpen ↗

Quoted message said:

Dani

--
Rick Onanian

Rick Onanian said:

asqui said:

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

Why only on the big chainring? Is it because that is where the derailer going to be at it's limit
and therefore less effective at forcing it onto the ring?

Imagine shifting from big ring to small: Chain falls off big ring, lands on smal..

Now imagine shifting from small to big: Chain must climb to big ring.

The chain could use a little help, so the gaps created by the smaller teeth result in some grabby
action on the chain.

Disclaimer: I am not an engineer, mechanic, lawyer, or police officer. I could be wrong.

Sorry, I forgot to make it clear that I have a skanky touring bike with a triple chainring, so
really my question is doesn't the same thing apply for when you are changing from granny to middle.

Quoted message said:

Quoted message said:

What orientation do I want these special teeth in, in relation to the cranks? 0 and 180 degrees
offset from the cranks so that they appear at top of the chainring when the cranks are at 6/12
o'clock with minimal being applied?

Probably not a concern; there may be some offset related to something else that matters, though.

What do you mean?

Quoted message said:

Quoted message said:

Another chainring question: There appears to be at least a few mm of wobble in the big and middle
chainrings, visible when I spin the cranks quickly and focus on the chainrings against the
background. Is this normal?

Yes, it's normal in so far as lots of people probably never even notice, let alone repair it.

Oh, that's comforting.

Quoted message said:

Quoted message said:

Can anything be done to corret it? I believe it was like this when I bought the bike and the LBS
didn't seem to think too much of it when I pointed it out.

Read this: sheldonbrown.comstraighten chw.htmlOpen ↗

Damn! And I thought I had read everything there was to read on that site!

Thanks for your help.

Quoted message said:

Quoted message said:

Dani

Quoted message said:

if that's not up to spec, you could trash the crank arm. On a couple of occasions, I've run across
setups where I was never able to get the damthing to stop rubbing in some particular gear
combination or condition, but most of the bikes I deal with are, for lack of a less diplomatic
description, crummy. Yours should be able to work without rubbing.

It's almost always a problem with the FD forward-aft alignment.

Also, use your barrel adjusters on your shifters while riding (if MTB).

--
Phil, Squid-in-Training

asqui said:

Sorry, I forgot to make it clear that I have a skanky touring bike with a triple chainring, so
really my question is doesn't the same thing apply for when you are changing from granny to middle.

It's helpful, but not essential. Fancy chainrings can help when shifting under load, but plain rings
worked fine for many years and still do. I just replaced my middle ring. The previous one was a
complex-shaped Shimano number. The replacement was plain. I've noticed very little difference. I
developed my habits in the "old days" and so I usually don't try front shift under heavy load.

asqui wrote: ...........

Quoted message said:

There are two pairs of these teeth, diametrically opposed, but they only appear on the big
chainring.

Why only on the big chainring?

It is also a feature of some middle rings.

Quoted message said:

What orientation do I want these special teeth in, in relation to the cranks?

It depends on make and model of chainrings and cranks. What have you got?

~PB