9 speed rear derailleur - 8 speed shifters & cassette

[pembo6]

Is there any reason a new 9 speed rear derailleur wont work with existing 8 speed rear cassette and 8 speed shifter?

I need to replace my dead shimano sora rear derailleur and was going to get a new 9 speed sora (they dont make 8 speed anymore). Can't justify a whole upgrade to 9 or 10 speed.

I don't see any reason why It wouldn't work perfectly. Unless the teeth on the pulley wheels are a different size and damage the 8 speed chain.

Can anyone confirm? Thanks.

[Velo13]

Should work just fine.

[funnybike]

The only reason it won't work is if your 8 speed shifters are the 7400 series Dura Ace. They have a different amount of cable pull and will only work with the matching derailleur. If it is any other shimano model, then it will work perfectly with the 9 speed rear derailleur.

[jules21]

Is there any reason a new 9 speed rear derailleur wont work with..

the only thing that counts is the pull ratio. there is no such thing as a "9 spd derailleur", that is just marketing spin.

[bosvit]

Is there any reason a new 9 speed rear derailleur wont work with..

the only thing that counts is the pull ratio. there is no such thing as a "9 spd derailleur", that is just marketing spin.

+1

I've been running 9 speed vitamin a, b, c, d and e rd with 8 speed sofa shifters for years. They came stock on my Trek 1000.

[Mustang]

I have run a 9 sp.,105 long cage Shimano 105 RD, with a 6 speed cassette, on my Vitus.
Its the shifter that does the work, the extra travel can be limited by the stop screws.

[pembo6]

Interesting....

I have been informed by Shimano Australia, Wiggle & ChainReaction that the 9sp rear derailleur will not work properly in place of the 8sp.

But I bought one new anyway, for $13.50 ......so who cares!

I bet it works just fine.

Thanks for the answers you posted.

[rifraf]

Interesting....

I have been informed by Shimano Australia, Wiggle & ChainReaction that the 9sp rear derailleur will not work properly in place of the 8sp.

But I bought one new anyway, for $13.50 ......so who cares!

I bet it works just fine.

Thanks for the answers you posted.

I use a 9 speed XT M772 derailleur on a 7 speed cassette.
However I do believe some 9 speed XT derailleurs only suited narrow 9 speed chains.
I saw this mentioned on the Wiggle site and based my purchase decision on it.
My XT derailleur was backwards compatible but apparently not all are:
Wiggle describes the M770 as: "Mega9 compatible for use with 9-speed drivetrains"
M771 as: "Mega9 compatible for use with 9-speed drivetrains"
Wiggle describes the M780 as: "Dyna-Sys 10-speed compatible only"
M780 Shadow as: "MTB 10-speed compatible only"

Wiggle describes My M772 as: "Mega9, 8 & 7 speed compatible"

Hope this helps

[rifraf]

Is there any reason a new 9 speed rear derailleur wont work with..

the only thing that counts is the pull ratio. there is no such thing as a "9 spd derailleur", that is just marketing spin.

I believe this is not entirely correct.
The fact that some do creates confusion.
See my other post to clarify.

It comes down to the spread of the derailleur as to whether the thicker (lower speed) chains will
travel through the cage.