shimano 9 spd rear shifter compatible with 8 spd chain?

[02GF74]

quickie: is a shimano 9 speed rear shifter compatible with 8 speed shimano chain?

and anyone using this combination and find it works?

 

[Dave Davenport]

Yep, run a tiagra 9 speed rear mech with sora 8 speed on mrs d's winter bike.

 

[andy_wrx]

Last year, when Sora was 8sp, lots of manufacturers were selling Sora bikes 'upgraded' with a Tiagra rear mech, e.g. Spesh Allez, Trek 1000

The mech doesn't 'know' how many gears you have and the inner width of the chain in the same so they ride the same tooth-width jockey wheels