Upgrading from 8 to 9 speed Sora

[Danny]

One of my bikes has 8 speed Sora shifters and a Sora rear deraileur. The mechanism on the right shifter is on its way out and needs to be replaced.

If I want to stick with Sora I need to buy 9 speed shifters as 8 speed are no longer available. My question is, will I also need to upgrade the rear deraileur?

I thought the indexing is all in the shifters not the deraileur, but I have received contradictory advice on this from two different bike mechanics.

 

[Drago]

The mech should have the capacity.

 

[adscrim]

I've used 9 speed shifters with a ten speed mech and 10 speed shifters with a 9 speed mech without issue. 105 on both occassions.

 

[Danny]

I've used 9 speed shifters with a ten speed mech and 10 speed shifters with a 9 speed mech without issue. 105 on both occassions.

So what is the difference between an 8 speed, 9 speed, and 10 speed deraileur?

 

[alecstilleyedye]

shimano claris is 8 speed…

 

[Drago]

So what is the difference between an 8 speed, 9 speed, and 10 speed deraileur?

on road bikes the width of a cassette it'll cover, and about 50 quid.

 

[adscrim]

So what is the difference between an 8 speed, 9 speed, and 10 speed deraileur?

Not sure - I would assume, as Drago says, it's the width of the the cassette but I think there is enough 'error' built in that going up one speed is well within limits. Obviously going down one speed is dealt with by limit screws.