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9 speed derraileur on 8 speed cassette?

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9 speed derraileur on 8 speed cassette?

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flag EdsE
Posted: Jan 15, 2009 at 10:27 Quote
My friend has some old crappy acera derry and shifter. So he would change it to Deore XT ones. The Deore Xt is 9 speed (shifter too). Can we just leave the chain and cassette and use the XT with 8 speed?

Thnx Big Grin
flag t3rry
Posted: Jan 15, 2009 at 10:29 Quote
Nope, the the spacing is different, so it will not shift properly. I have done this on an old junker and managed to get it to shift somewhat normally - but it shouldn`t be done.
flag mrclownprince
Posted: Jan 15, 2009 at 10:32 Quote
EdsE wrote:
My friend has some old crappy acera derry and shifter. So he would change it to Deore XT ones. The Deore Xt is 9 speed (shifter too). Can we just leave the chain and cassette and use the XT with 8 speed?

Thnx Big Grin

yes you can use the derailer on the 8 speed cassette. The major difference between 8 and 9 speed is indexing. So for an 9 speed cassette you would need 9 speed shifters.

I have used Acera 8 speed shifters on Deore LX derailler. Actually the acera shifters are not all that bad. Raced two seasons on those.

whOops, on edit, don't use the XT 9 speed shifters.
flag mrclownprince
Posted: Jan 15, 2009 at 10:34 Quote
terri- wrote:
Nope, the the spacing is different, so it will not shift properly. I have done this on an old junker and managed to get it to shift somewhat normally - but it shouldn`t be done.

Spacing is not different. Your thinking 7 speed.

8 speed and 9 speed use the same width cassette. only the cogs are thinner on the 9 speed.

a derrailer that can move from the bottom to the top of an 8 speed can do the same on 9 speed, it is controlled by the shifters though for alignment with the gears.

spacing wise, 9 speed and 8 speed have the same freehub width on shimano and SRAM cassettes.
flag EdsE
Posted: Jan 15, 2009 at 10:40 Quote
Thanx for the fast replies. So wil it work like good or not as good as with an 8 speed shifter/derri?
flag t3rry
Posted: Jan 15, 2009 at 10:45 Quote
Hmmm.. I'll get a more informed mechanics opinion in here. I've always been told never to mix anything 9 speed with 8 speed - even though I've managed to get it to work somewhat well before.

Learn something different everyday.
flag almightybenners
Posted: Jan 15, 2009 at 10:54 Quote
yeah its fine my brother runs an eight speed lx cassette with the xt shadow derailluer fine but you cant run a 9 speed shifter with an eight speed cassette because of cable pull and the such
flag t3rry
Posted: Jan 15, 2009 at 11:13 Quote
All right - I resorted to Sheldon Brown as none of my mechanic friends are around at the moment, and it matches what I've been taught in the past. So from what I understand from this - the Shifter needs to be 8 speed to match the spacing of the cassette (between 8 speed and 9 speed there is about a half mm difference per spacing). The derailer should work as long as it is mated with the correct shifter for the cassette.

"Bicycle Gears: 6-speed, 7-speed, 8-speed, 9-speed, 10-speed?
Component manufacturers like to sell you lots of new parts, even if you don't need them. This has led to much confusion as various parts are labeled as if they are incompatible with other parts even though they are actually usable with little or no problem.
The following parts only are "speed specific":

Indexed Shifters These need to have the correct number and spacing of detents ("clicks") to match the system they'll be used with. (Friction shifters have no compatiblity issues, they work with everything.)

Cassettes It is really the cassette that determines how many speeds you have in back.
Campagnolo/Shimano 8-speed cassettes have different spacing , so you can't generally get good indexing using a Campagnolo 8-speed wheel with a Shimano shift system or vice versa.

With 7-, 9- and 10-speed systems, the sprocket spacing between brands is close enough that it rarely causes any difficulty in practice.

For perfect matching, you might substitute different spacers or use a Jtek Shift Mate pulley adaptor.

See my "Apacing Cribsheet " for more details on this.


Chain As you go to more sprockets on the cassette, you need a narrower chain. However, using a narrower chain with an older system rarely presents any problem. Thus, you can use a "9-speed" chain with a 7-speed or 8-speed system, or a "10-speed" chain with a 9-speed system. Since the chains designated for more gears are usually more expensive and don't last as long, this is not the ideal approach, but it's perfectly workable."
flag jonbikes
Posted: Jan 16, 2009 at 11:44 Quote
Sheldon Brown is a great resource.

Just to clear this up, there is no such thing as an 8 or 9 spd derailleur, one does both.
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