add third chainring?

[email hidden] (Chandler=A0Webb) asked:

Quoted message said:

Hi folks,

I have an old Shimano "Light Action SIS" 12 speed system, and I'd like to add a third chainring to
give it a lower range for hills.

It looks as though the front derailleur will adjust to accommodate a longer shifting range.
I'll have to look into a longer rear cage for the chain slack. How do I calculate the correct
chain length?

This is done after the new gears and deraileurs are installed. Lace the chain around the largest
cog, chainring and through both of the deraileurs.

Now pull it taught so the rear derailleur cage is stretched all the way forwards, then add a
couple of links.

Quoted message said:

The (Sakae) crank has holes for the smaller chainring, but it looks as though it might need spacers
to mount it away from the inner chainring. Are these spacers commonly available parts?

Yes, Spacers are required to separate the smallest chainring from the crank arms. Just ask your
LBS for some. They'll probably run you about a buck each nowadays. It's been a while since I've
bought any.

Quoted message said:

Can I simply order a Shimano 32 tooth (5 bolt) chainring, maybe for a 105 series, and install it,
or am I missing something? Is there going to be a difference in tooth spacing?

Quoted message said:

Thanks for any help.
--
Chan Webb

Tooth spacing is one of the few things on a bicycle that is truly universal. 1/2" pitch, world wide
(why it hasn't gone metric, I don't know).

As to which five arm chainring you need, that depends on the type of crank spider (the five
arms) you have.

There are basically two sizes for a triple: Traditional and "Micro drive" (64 and 58 mm, I think).
Regardless of which type you end up with, you will still net the spacers. Be sure you tell the
dealer it's a six speed, ot a nine. Nine speed chain rings are spaced differently.

May you have the wind at your back. And a really low gear for the hills! Chris

Chris'Z Corner "The Website for the Common Bicyclist": geocities.comczcornerOpen ↗

Chandler Webb said:

It looks as though the front derailleur will adjust to accomodate a longer shifting range.
I'll have to look into a longer rear cage for the chain slack. How do I calculate the correct
chain length?

Worry about that when you get all the parts. There are a number of methods, but there is one
absolute necessity. With the chain on the biggest chainring and the biggest cog. it has to be able
to fit (in the derailleur, too). Otherwise, you are asking for trouble. You'll need a long-cage
deraileur to be able to do this, and use the granny on a reasonable number of cogs as well.

Quoted message said:

The (Sakae) crank has holes for the smaller chainring, but it looks as though it might need
spacers to mount it away from the inner chainring. Are these spacers commonly available parts?

They are washers. Hardware stores have plenty. Not specific for this crank, but the original
equipment will be impossible to find.

Quoted message said:

Can I simply order a Shimano 32 tooth (5 bolt) chainring, maybe for a 105 series, and install it,
or am I missing something? Is there going to be a difference in tooth spacing?

Not a difference in tooth spacing, but huge differences in the spacing for the bolts used to attach
the chainring. You have to find out the diameter of the bolt circle (the circle passing through the
centers of the chainring bolts). This can be 74mm, 58mm, or a number of other choices.

--

David L. Johnson

__o | And what if you track down these men and kill them, what if you _`\(,_ | killed all of us?
From every corner of Europe, hundreds, (_)/ (_) | thousands would rise up to take our places.
Even Nazis can't kill that fast. -- Paul Henreid (Casablanca).

(Chris Zacho 'The Wheelman') said:

Tooth spacing is one of the few things on a bicycle that is truly universal. 1/2" pitch, world wide
(why it hasn't gone metric, I don't know).

Because it's a universal standard. Going to a longer pitch would be Bad for small sprockets, because
now you need a 10 tooth in the rear where you used to have an 11, *or* your 54 tooth chainring in
front becomes big enough to hit the ground, and lowering the pitch would be Bad because it would be
a more expensive chain with more parts. And both are Bad because, as you say, they're nonstandard.

Jasper