Shimano Index and Old Suntour RDs

[pinnah]

I'm running Shimano 8-speed Barcon shifters with a Shimano 8-speed rear
cluster and Shimano RD. The system works just fine.

Would there be any shifting issues if I swapped out the Shimano RD for an
older Suntour GT (long cage) RD?

I'm expecting that the Suntour RDs would be a bit more intollerant and
nervous since they don't have a "floating" top jockey pulley. Would I be
correct in thinking that this combo might shift OK in non-indexed mode but
would be jumpy in indexed mode due to this?

Related, I'm assuming (perhaps incorrectly) that the indexing is primarily
dictated by the compatability of the indexed shifter (the 8 speed barcon in
this case) and the rear cluster spacing, no? That is, am I correct that
the design of the RD has no real affect on the indexing so long as it has
enough travel (and noting the jockey wheel issue).

Thanks,

Dave

 

[Andy M-S]

Alas, the design of the RD has a major impact--different RDs move
different distances for a given cable pull. I'm pretty sure that the
setup you propose will not index correctly.

 

[[email protected]]

You can use friction and it will shift like a dream, but if you want it
to index you'll have to get a Shimano der. It's not just a rear
cluster spacing thing, it's also a cable travel thing. The shimano and
suntour rear ders work only with shimano and suntour shifters. However
they will work in friction mode just fine.
-Tim

 

[Michael Press]

In article
<[email protected]>,
"[email protected]" <[email protected]> wrote:

> You can use friction and it will shift like a dream, but if you want it
> to index you'll have to get a Shimano der. It's not just a rear
> cluster spacing thing, it's also a cable travel thing. The shimano and
> suntour rear ders work only with shimano and suntour shifters. However
> they will work in friction mode just fine.

What are you talking about?

--
Michael Press

 

[Dave Mayer]

"pinnah" <[email protected]> wrote in message
news:[email protected]...
> I'm running Shimano 8-speed Barcon shifters with a Shimano 8-speed rear
> cluster and Shimano RD. The system works just fine.
>
> Would there be any shifting issues if I swapped out the Shimano RD for an
> older Suntour GT (long cage) RD?
>
> I'm expecting that the Suntour RDs would be a bit more intollerant and
> nervous since they don't have a "floating" top jockey pulley. Would I be
> correct in thinking that this combo might shift OK in non-indexed mode but
> would be jumpy in indexed mode due to this?
>
> Related, I'm assuming (perhaps incorrectly) that the indexing is primarily
> dictated by the compatability of the indexed shifter (the 8 speed barcon
> in
> this case) and the rear cluster spacing, no? That is, am I correct that
> the design of the RD has no real affect on the indexing so long as it has
> enough travel (and noting the jockey wheel issue).
>
> Thanks,
>
> Dave

Dave: the Suntour GT will not index with your shifters and cassette. Why?
Because of the geometry of the rear derailleur. Derailleurs from different
makers may have different geometries.

Time for some math: your 8-speed Shimano barcons pull about 2.9mm of cable
per click. Your Shimano derailleur travels 1.67mm per mm of cable pull.
The result is that your derailleur travels 4.8mm per click, which is the cog
spacing (cog center to center) standard for Shimano 8-speed.

The old Suntour derailleurs travelled about about twice as much as the
amount of cable pull. So, roughly, 2.9 x 2 will give you 5.8mm of
derailleur travel per click. This does not match the spacing of any
cassette or freewheel that I'm aware of. So the derailleur will overshoot
when you are shifting from smaller to bigger cogs.

Besides, a current Shimano unit, even the cheap stuff such as Alivio will
shift much more precisely than an old GT. Even in friction.

 

[Luns Tee]

In article <oRwKf.52205$sa3.12497@pd7tw1no>,
Dave Mayer <[email protected]> wrote:
>Time for some math: your 8-speed Shimano barcons pull about 2.9mm of cable
>per click. Your Shimano derailleur travels 1.67mm per mm of cable pull.
>The result is that your derailleur travels 4.8mm per click, which is the cog
>spacing (cog center to center) standard for Shimano 8-speed.

I'm curious - how do the numbers for Dura-Ace compare?

>The old Suntour derailleurs travelled about about twice as much as the
>amount of cable pull. So, roughly, 2.9 x 2 will give you 5.8mm of
>derailleur travel per click. This does not match the spacing of any
>cassette or freewheel that I'm aware of. So the derailleur will overshoot
>when you are shifting from smaller to bigger cogs.

Hmm.. my impression of Accushift era derailleurs was that they
have a cable pull of about 90% of (non Dura-Ace) Shimano's for the
same travel, or about the same as pre-97 Dura-Ace. Were the earlier
Suntour derailleurs even more sensitive?

-Luns

 

[A Muzi]

pinnah wrote:

> I'm running Shimano 8-speed Barcon shifters with a Shimano 8-speed rear
> cluster and Shimano RD. The system works just fine.
>
> Would there be any shifting issues if I swapped out the Shimano RD for an
> older Suntour GT (long cage) RD?
>
> I'm expecting that the Suntour RDs would be a bit more intollerant and
> nervous since they don't have a "floating" top jockey pulley. Would I be
> correct in thinking that this combo might shift OK in non-indexed mode but
> would be jumpy in indexed mode due to this?
>
> Related, I'm assuming (perhaps incorrectly) that the indexing is primarily
> dictated by the compatability of the indexed shifter (the 8 speed barcon in
> this case) and the rear cluster spacing, no? That is, am I correct that
> the design of the RD has no real affect on the indexing so long as it has
> enough travel (and noting the jockey wheel issue).

A Suntour GT not only lacks the floating upper pulley, it's
also old technology in that it lacks the upper pivot spring
and has dated cage shape/roller position. Any new $14.95
derailleur will outperform it in any way you'd care to measure.
Will it work? Sure. Well? Not by modern standards. Indexing
with your present system is out.

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

 

[pinnah]

All, huge thanks for helpful guidance! Looks like I'll just stick with
the current Shimano RD.

It's so nice to learn something new! Thanks a ton.

Dave

 

[Dave Larrington]

In article <[email protected]>, pinnah
([email protected]) wrote:
> I'm running Shimano 8-speed Barcon shifters with a Shimano 8-speed rear
> cluster and Shimano RD. The system works just fine.
>
> Would there be any shifting issues if I swapped out the Shimano RD for an
> older Suntour GT (long cage) RD?
>
> I'm expecting that the Suntour RDs would be a bit more intollerant and
> nervous since they don't have a "floating" top jockey pulley. Would I be
> correct in thinking that this combo might shift OK in non-indexed mode but
> would be jumpy in indexed mode due to this?
>
> Related, I'm assuming (perhaps incorrectly) that the indexing is primarily
> dictated by the compatability of the indexed shifter (the 8 speed barcon in
> this case) and the rear cluster spacing, no? That is, am I correct that
> the design of the RD has no real affect on the indexing so long as it has
> enough travel (and noting the jockey wheel issue).

A mate of mine ran for a while a setup consisting of Sachs twist-grip
shifters, 8-speed Shimano block and Sun Tour VX GT rear mech and
reported that it indexed OK.

--
Dave Larrington - <http://www.legslarry.beerdrinkers.co.uk/>
Electricity comes from other planets.

 

[dvt]

Luns Tee wrote:
> In article <oRwKf.52205$sa3.12497@pd7tw1no>,
> Dave Mayer <[email protected]> wrote:
>> Time for some math: your 8-speed Shimano barcons pull about 2.9mm of cable
>> per click. Your Shimano derailleur travels 1.67mm per mm of cable pull.
>> The result is that your derailleur travels 4.8mm per click, which is the cog
>> spacing (cog center to center) standard for Shimano 8-speed.
>
> I'm curious - how do the numbers for Dura-Ace compare?

According to http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3946, old
Dura-Ace derailers moved 1.9 mm / mm of cable pull.

--
Dave
dvt at psu dot edu

 

[Ryan Cousineau]

In article <[email protected]>,
[email protected] (Luns Tee) wrote:

> In article <oRwKf.52205$sa3.12497@pd7tw1no>,
> Dave Mayer <[email protected]> wrote:
> >Time for some math: your 8-speed Shimano barcons pull about 2.9mm of cable
> >per click. Your Shimano derailleur travels 1.67mm per mm of cable pull.
> >The result is that your derailleur travels 4.8mm per click, which is the cog
> >spacing (cog center to center) standard for Shimano 8-speed.
>
> I'm curious - how do the numbers for Dura-Ace compare?

Dura-Ace 8, as you are alluding to, is special. Here's the most complete
article on Campy/Shimano intercompatibilities I know of. It has a
section on Dura-8:

http://www.ctc.org.uk/DesktopDefault.aspx?TabID=3946

> >The old Suntour derailleurs travelled about about twice as much as the
> >amount of cable pull. So, roughly, 2.9 x 2 will give you 5.8mm of
> >derailleur travel per click. This does not match the spacing of any
> >cassette or freewheel that I'm aware of. So the derailleur will overshoot
> >when you are shifting from smaller to bigger cogs.
>
> Hmm.. my impression of Accushift era derailleurs was that they
> have a cable pull of about 90% of (non Dura-Ace) Shimano's for the
> same travel, or about the same as pre-97 Dura-Ace. Were the earlier
> Suntour derailleurs even more sensitive?

"Suntour Accushift systems are variegated spacing!

"Unlike Campagnolo EXA or Shimano HG systems, Suntour Accushift cog
spacing is wider between the high gears and narrower at the low end."

http://www.yellowjersey.org/accu.html

I'm not certain, but I think the later Suntour systems (Accushift Plus?)
were Shimano-compatible, just as SRAM's MRX line of shifters is.

--
Ryan Cousineau [email protected] http://www.wiredcola.com/
"I don't want kids who are thinking about going into mathematics
to think that they have to take drugs to succeed." -Paul Erdos

 

[Dave Mayer]

"Luns Tee" <[email protected]> wrote in message
news:[email protected]...

> I'm curious - how do the numbers for Dura-Ace compare?
>
>>The old Suntour derailleurs travelled about about twice as much as the
>>amount of cable pull. So, roughly, 2.9 x 2 will give you 5.8mm of
>>derailleur travel per click. This does not match the spacing of any
>>cassette or freewheel that I'm aware of. So the derailleur will overshoot
>>when you are shifting from smaller to bigger cogs.
>
> Hmm.. my impression of Accushift era derailleurs was that they
> have a cable pull of about 90% of (non Dura-Ace) Shimano's for the
> same travel, or about the same as pre-97 Dura-Ace. Were the earlier
> Suntour derailleurs even more sensitive?
>
> -Luns
>
Luns: very good. You know your stuff. The mechanical advantage for old
Dura-Ace was about 10% higher than the rest of the Shimano line. I
calculate the ratio of derailleur travel to cable pull as 1.83 to 1. Which
is very close to the Accushift Suntour derailleurs. I have tried a Suntour
XC Pro derailleur on a bike with 8-speed Dura-Ace STI shifters and cogset.
Shifted beautifully.

Pre-indexing Suntour derailleurs, such as the old GT unit (which started
this whole thread off) had an even higher mechanical advantage - around 2 to
1. These units required precise shifting. Before the indexing requirement,
the design of the derailleur cages and slant angle was not standardized, so
that the mechanical advantage varied from model to model.