9 speed derailleur compatible with 8 speed drivetrain?

[cristal]

Hi Guys, bought a MTB for son, just to get to school and back 8 speed shimano, RDis a alivio, I have a old 9 speed XT RD lying around, will this work, taking into account the chain thickness and 8 speed cluster on the back.

 

thanks

[PeterF]

No unfortunately it will not work.  The indexing of the 9 spd derailleur is not the same as the 8 spd derailleur.

[Moriarty]

In your position I would just try it and see, I'm pretty sure it will work.

[cristal]

thanks

[s14phoenix]

it should work... I fitted an 9sp SLX on alivio 8sp shifters. The pull ratio of 8 alivio and 9sp is the same on those... the shifters will shift the 8sp

 

Tried, tested, works.

 

you might need to lengthen or shorten the chain as the alivio derailleur has bigger pulleys...

[the nerd]

No unfortunately it will not work.  The indexing of the 9 spd derailleur is not the same as the 8 spd derailleur.

 

Indexing is in shifters and nowhere else.

 

It should work fine.

[Long Wheel Base]

Indexing is in shifters and nowhere else.

 

It should work fine.

THIS

 

You would only have to worry about the deraileur pull and 7,8,9 is all the same.

Chain width is also the same for the 3 above mentioned.

[DJR]

...............7,8,9 ............

Chain width is also the same for the 3 above mentioned.

This is what I've learnt today.   (I know 9 and 10 are different widths because my 10 speed links failed to fix my buddies snapped 9 speed chain out on the road.)

[PeterF]

Indexing is in shifters and nowhere else.

 

It should work fine.

Cool thanks, learnt something new today.

[Long Wheel Base]

This is what I've learnt today.   (I know 9 and 10 are different widths because my 10 speed links failed to fix my buddies snapped 9 speed chain out on the road.)

And then 11s is even narrower.

[popcorn_skollie]

it will be fine.

I had a 9 speed deore derailleur on an old 8 speed cassette and 8 speed shifter and it worked flawlessly.

Fit some new cables while you at it and presto.

[Onegear]

THIS

 

You would only have to worry about the deraileur pull and 7,8,9 is all the same.

Chain width is also the same for the 3 above mentioned.

If they the same thickness, could you run an 8 speed chain on a 9 speed groupset ?

[velomonatiCT]

Hi Guys, bought a MTB for son, just to get to school and back 8 speed shimano, RDis a alivio, I have a old 9 speed XT RD lying around, will this work, taking into account the chain thickness and 8 speed cluster on the back.

 

thanks

 

im confused is the original RD broken ????

 

if not then why .......

[Long Wheel Base]

If they the same thickness, could you run an 8 speed chain on a 9 speed groupset ?

Ok its gets technical if you really look into it. 7, 8, and 9 speed chains have the same inner width, but 9 speed chains have thinner outer plates for a thinner overall chain. So while a 9 speed chain works fine on a 7 or 8 speed drivetrain, it will be a weaker chain that tends to "stretch" faster. So if your looking for durability then i'd say Yes run an 8 speed chain but i'm also not sure how many LBS still sell 8 speed specific chains. The spacers between each gear on the 7,8 and 9 speed clusters are the same so I don't see why it wont work.

[Broker]

No unfortunately it will not work.  The indexing of the 9 spd derailleur is not the same as the 8 spd derailleur.

Indexing is not controlled by the derailleur but by the shifter. So if its 8 spd shifter with 8 spd cluster it should not be a problem. The only issue might be the width of the chain going through the derailleur.

[NotSoBigBen]

Indexing is not controlled by the derailleur but by the shifter. So if its 8 spd shifter with 8 spd cluster it should not be a problem. The only issue might be the width of the chain going through the derailleur.

 

I am always unsure when that statement is made as to my knowledge there is difference when for example going 9sp to 10sp .... it is as stated here true perhaps for 7,8,9 but not 9,10 or even 11? So yes it is controlled by the shifter but there are some differences in RD when going above 9, would that be correct to say?