Stretching a Tiagra derailleur's capacity?

[[email protected]]

A cyclist I know in a remote city needs some help. He's got a
Cannondale road bike, about two years old, with a triple crank and a
Tiagra rear derailleur.

He's tried to climb some of the fierce hills in his area, and he needs
lower gears.

I've asked for a tooth count, and I was told the frong granny ring is
30t, the rear is 25. I also asked for the distance between the
derailleur idler pulley's axles, and they responded "3 1/4 to 3 1/2
inches."

I've actually got an almost new Tiagra derailleur in my junk box, from
when we put lower gears on my daughter's bike. I suspect that
derailleur is identical (since both bikes came with triples) but I
measure almost exactly 3" between idler axles. And although I doubt
it's pertinent, the bike in question has Sora brifters (with the
thumb-style upshift buttons) and may be an 8 speed - I forget.

Looking at specs in a Shimano booklet, the Tiagra RD-4400-GS derailleur
is listed as having a 27 tooth max sprocket, 22 tooth max front
difference, and 37 tooth total capacity.

How much can we stretch that, especially the max rear sprocket? Any
chance of getting a 30 tooth to work in the rear without changing the
derailleur?

Oh, and I'm willing to spell it "derailer" if it will coax Sheldon to
answer. ;-)

- Frank Krygowski

 

[dvt]

[email protected] wrote:
> Looking at specs in a Shimano booklet, the Tiagra RD-4400-GS derailleur
> is listed as having a 27 tooth max sprocket, 22 tooth max front
> difference, and 37 tooth total capacity.
>
> How much can we stretch that, especially the max rear sprocket? Any
> chance of getting a 30 tooth to work in the rear without changing the
> derailleur?

Almost everyone will say you can stretch to 28t cog, most will say you
can use 30t cog. I've used 28t on a Shimano derailer rated for 27t with
no trouble. And you can stretch the 37t total capacity a bit, but I
don't have a number for you.

--
Dave
dvt at psu dot edu

 

[Qui si parla Campagnolo]

[email protected] wrote:

>
> Looking at specs in a Shimano booklet, the Tiagra RD-4400-GS derailleur
> is listed as having a 27 tooth max sprocket, 22 tooth max front
> difference, and 37 tooth total capacity.
>
> How much can we stretch that, especially the max rear sprocket? Any
> chance of getting a 30 tooth to work in the rear without changing the
> derailleur?
>
> Oh, and I'm willing to spell it "derailer" if it will coax Sheldon to
> answer. ;-)
>
> - Frank Krygowski

Derailleur...Use as much as a 30t w/o problem, any bigger and a l o n g
cage
MTB rear der would probably be a better idea. 'Road' long cage rear
ders are really 'medium' cage, when compared to MTB cage rear ders.

 

[Booker C. Bense]

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

In article <[email protected]>,
<[email protected]> wrote:
>A cyclist I know in a remote city needs some help. He's got a
>Cannondale road bike, about two years old, with a triple crank and a
>Tiagra rear derailleur.
>
>
>
>Looking at specs in a Shimano booklet, the Tiagra RD-4400-GS derailleur
>is listed as having a 27 tooth max sprocket, 22 tooth max front
>difference, and 37 tooth total capacity.
>
>How much can we stretch that, especially the max rear sprocket? Any
>chance of getting a 30 tooth to work in the rear without changing the
>derailleur?
>

_ I've used that derailler with a 30t rear cog and it worked just
fine with the proper B screw adjustment. You can push the total
capacity by quite a bit if you stay out of the small/small
combos. I've personaly gone as high as 40t total capacity w/o
any problems.

_ Booker C. Bense


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