Can I use a 10 speed mech on a 9 speed drivetrain ?

[Seight_Returns]

Currently transplanting components from an old road bike onto a new Ribble frame.

It's a mix of Sora 3400 and Tiagra 4500 9 speed components.

I need a new rear mech - ideally I'd like a Tiagra 4500 but can't find one - I can get a newer Tiagra 4601 10 speed mech at a good price from CRC.

Will the 10 speed mech work ok with the 9 speed drivetrain ? I think it should since all the indexing is an the shifters - but wanted to check.

I realise that a Sora 3400 or 3500 9 speed mech is an option, but I'd like to have Tiagra components for no other reason than snob value.

[gazza285]

I've run a wild and varied mixture of Shimano stuff on my fleet and never had a problem, as you say the indexing is in the lever, and all Shimano stuff has the same pull ratio so go for it.

[Disco You]

I know for certain that 5700 front and rear derailleurs work on an otherwise 4500 groupset, so I am inclined to say yes.

[upsidedownmark]

In a word - yes.

Opposite way round, I'm still running a 5 year old 105 mech with 6700 ultegra, you'd never know.

[itsnotarace]

The movement in the rear mech is governed by the shifters (specifically the amount of cable they release or pull to change to the next cog in either direction as part of the indexing), so yes it will work fine.