Shimano Sora/Tiagra compatibility (8 v 9-speed)

blim

Hi

This has probably been asked before, so apologies in advance. I have a Giant SCR3, which is mostly Sora (triple). If I wanted to upgrade the front mech to Tiagra (triple), would it work with my current 8-speed chain? And would moving to a narrower 9-speed chain still work with the 8-speed cassette?

noggincp

yes and yes

done exa\tly that on my Spesh Allez

andy_wrx

I used 9sp 105 front & rear mechs with a Sora 8sp triple system for a while, found it a bit difficult to set-up the front mech so as to be able to use all the gears without lots of chain-rubbing.
Sora doesn't have the trim facility of higher-group shifters, I found I could only set it up so as to use about 5 or 6 of the cogs when on the middle ring, I presume because the 9sp mech is narrower
But running a 9sp chain however it was fine.

stueyc

how does the trim facility work?

andy_wrx

For a triple, it doesn't just has the 3 clicks to go from inner - middle - outer, there's like a lesser click in the middle.
You use it on the middle ring, it moves the front mech just a bit, enough to move it sideways a bit and stop the chain rubbing, without moving it enough to shift to the inner or outer ring.
So you set it up to use the smaller half of the rear cassette without rubbing, when you move over to the bigger half of the rear cassette it'll start to rub so you trim, moving the mech enough to stop it rubbing and let you use the bigger half of the cassette.

In the olden days, without STI clickstops, you could easily do this with a friction shifter.

But Sora doesn't have it (dunno if Tiagra does, think 105 does, Ultegra certainly does and I use it).
I couldn't manage, with 9sp 105 front mech and 8sp chain, to set it up so that I could use all of the cassette when in the middle ring - I had it rubbing if I used the biggest or smallest ends of the cassette, which forced me to shift to the outer or inner rings.

stueyc

i have bianchi 9 speed compact..lbs said i had trim facility....i have rubbin on smaller cogs,can this help me?

Ste_S

The only drivetrain parts that are speed specific are the shifters, chain and cassette. The Tiagra front mech will work fine with 8spd shifters and chain.

I wouldn't bother changing to a 9spd chain unless you're changing the shifters and cassette too - they're more expensive than an 8spd and wear quicker.

John.T

I would not recommend using a 9sp front mech on an 8sp set up as the cage is norrower and will be more prone to chain rub. Unless the mech is damaged why change it at all as it is one of the last things to wear out.
I have actually gone the other way and run a Sora front mech on my 9sp winter bike and an Ultegra 9sp one on my 10sp summer one. The Sora was cheap but works fine and the Ultegra was left over when I converted from 9sp. Both are running on compact chainsets and give no trouble at all. I can run all 20 gears on the 10sp without the need to trim.