# 9 speed derailleur on a 8 speed set up?



## AntonioLekic (Oct 25, 2013)

Hi everybody.
Iam thinking of upgrading my rear derailleur.I ve got a 8 spd shimano alivio and i would like to upgrade it to a Shimano Deore RD-M592 Shadow but i have a 8 spd casette,shifters and other.Could i do this without changing anything(for now) and then later buying a new cassete,shifters...
*And what are the side effects thanks!!!*


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## whoda*huck (Feb 12, 2005)

Edited for being wrong....apparently, yes you can.


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## Joules (Oct 12, 2005)

Yes, it will work fine if the shifters are shimano. Pull ratio is the same with shimano 8 and 9s. In the early days of 9s it was common for new bikes to come set up with 9s rear derailleurs.

a 10s rear derailleur will not work.


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## watts888 (Oct 2, 2012)

yes. If it's just the derailure. If you changed shifters without changing the cassette or the cassette without changing shifters, that's when you'd get the messed up shifting.

Edit: worse case scenario, If you get any binding of the chain inside the derailure (which you won't) you can switch to a 9-speed chain. The 9-speed chains have the same internal width as the 8-speed. the external width (thickness of the chain walls) is less on a 9-speed chain to clear the smaller space between the rings on a 9-speed cassette.


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## jtmartino (Jul 31, 2008)

whodaphuck said:


> No. Side effects will be crappy shifting in all but a couple of gears.


This is wrong.

Antonio, you'll be fine. The cable pull is the same and the derailleur cage can accommodate the slightly wider chain.


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## whoda*huck (Feb 12, 2005)

I stand corrected. It's been so long since I had anything with 8 speed....


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## AntonioLekic (Oct 25, 2013)

So I should upgrade it?Thank you guys for your help.Any experience with that Shimano Deore RD-M592 Shadow?Is it hard to mount it and will i need any other parts like bolts and screwes?


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## jtmartino (Jul 31, 2008)

What's wrong with the current derailleur? Is it broken? Not working properly?

You won't need any extra parts, although the derailleur will need to be adjusted properly. This can be a bit challenging for a beginner since you can really screw up your drivetrain/frame or get hurt if you don't do it right.


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## AntonioLekic (Oct 25, 2013)

Well my derailleur is 3 years old and its been threw a lot.Its a bit scew and it doesnt shift properly.Plus i kneed something a bit better i really love MTB.My neighbour is very handy and hes a good cyclist so he would help me mount it.


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## Shakester (Jun 26, 2012)

Many of the older 9 speed derailleurs are usually sold as 8/9 speed so its not uncommon for people running 9 speed derailleurs on an 8 speed set up. If you're relatively handy with a bike, then its a very easy switch and you won't need any other hardware. You'll need a chain breaker if your current chain doesn't have a link that you can disconnect such as a Sram/KMC powerlink. After removing the chain, its as easy as removing your old one with an allen wrench and throwing on the new one (you can also use loctite to insure that it doesn't loosen during a ride). After reinstalling the chain, the hardest part is setting the limit screws.


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## watts888 (Oct 2, 2012)

9-speeds are nice, but unless you're running out of gears, not necessary. I really don't think my 9-speed (11x34) gives me any more option than my 8-speed (11x32) because the low end gears are pretty close. A new cassette may be all you really need, especially if you have the stupid "Mega-range" ring.

Amazon.com: Shimano HG51 8-Speed Cassette: Sports & Outdoors


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## jtmartino (Jul 31, 2008)

watts888 said:


> 9-speeds are nice, but unless you're running out of gears, not necessary. I really don't think my 9-speed (11x34) gives me any more option than my 8-speed (11x32) because the low end gears are pretty close. A new cassette may be all you really need, especially if you have the stupid "Mega-range" ring.
> 
> Amazon.com: Shimano HG51 8-Speed Cassette: Sports & Outdoors


This. ^ Derailleurs usually don't go out unless you crash or lay the bike down too hard on the drivetrain side.

More likely you just need a new cassette.


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## whoda*huck (Feb 12, 2005)

jtmartino said:


> This. ^ Derailleurs usually don't go out unless you crash or lay the bike down too hard on the drivetrain side.
> 
> More likely you just need a new cassette.


Very likely, but after 3 years (depending on your mileage) prepare for the possibility that the chain and at least the small chain ring may also need to be changed.


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## jtmartino (Jul 31, 2008)

whodaphuck said:


> Very likely, but after 3 years (depending on your mileage) prepare for the possibility that the chain and at least the small chain ring may also need to be changed.


True. Funny how an inquiry about a simple derailleur turned into a drivetrain replacement...


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## eb1888 (Jan 27, 2012)

Often after this length of time two other things should be checked. The housing/cable and the lower derailleur pulley.
A lined housing and coated stainless cable can transform shifting performance.
Novara Shift Cable Kit - Free Shipping at REI.com
This is a Jagwire product. The best use is to run it full length by drilling out your intermediate stops to get rid of those extra ferules. The drag as they wear is what screws up your shifting.

The derailleur lower pulley teeth each has a chamfered edge to help guide the chain as it moves on an angle forward to the chain rings on the crank. It wears and doesn't work after a while. So inspect it and replace with an XT. The upper pulley is plain. You can see it on the left pulley.


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## lyra (Oct 21, 2013)

Before investing in a new rear mech, make sure that this is really what is causing you problems. This is what you do:

Take you bike to the LBS and ask them to check 3 things: 

1. The chain wear. If the chain is worn, replace the chain/cassette. Running with a worn chain damages your cogs and rings, and running a new chain on a worn cassette will prematurely wear out the chain. Replace both if the chain is kaput.

2. The derailleur hanger alignment. If the hanger is bent, have the shop bend it back or replace it. 

3. The shift cables and housing. Is there a lot of friction in there? That could cause imprecise shifting. (This is what I might check first if my shifting was inconsistent and requiring constant tuning).

If you do decide to replace your derailleur, go for 9 speed. Then you're all set if/when you decide to upgrade your shifters/cassette. There is no disadvantage to using a 9 spd derailleur with an 8 speed cassette, the pull ratio is exactly the same as for the 8 speed.


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## slapheadmofo (Jun 9, 2006)

lyra said:


> If you do decide to replace your derailleur, go for 9 speed. Then you're all set if/when you decide to upgrade your shifters/cassette. There is no disadvantage to using a 9 spd derailleur with an 8 speed cassette, the pull ratio is exactly the same as for the 8 speed.


Just for clarity, a derailleur originally marketed for either 7, 8 or 9 speeds can work fine with with any of those number of gears (though you don't want to mix together SRAM/Shimano shifters and derailleurs pretty much as a rule). The shifter on the bars does all the positioning; the derailleur simply goes where the shifter tells it to; the derailleurs themselves are not at all specific to a certain number of gears. I'm pretty sure you you wouldn't have a problem using something originally designed for 5 or 6 rear cogs either in a pinch.

I'm not totally up to speed on 10 and 11 speed compatibility - I believe you can get away with mixing 9 and 10, but can't swear to it. The issues have to do with chain width though, no specifically how many gears there are, but the tighter spacing required by jamming more gears into the same spacing.


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## lyra (Oct 21, 2013)

slapheadmofo said:


> Just for clarity, a derailleur originally marketed for either 7, 8 or 9 speeds can work fine with with any of those number of gears (though you don't want to mix together SRAM/Shimano shifters and derailleurs pretty much as a rule). The shifter on the bars does all the positioning; the derailleur simply goes where the shifter tells it to; the derailleurs themselves are not at all specific to a certain number of gears. I'm pretty sure you you wouldn't have a problem using something originally designed for 5 or 6 rear cogs either in a pinch.


Even though the shifter controls how much cable is pulled, the mechanical design of the derailleur determines how far the derailleur moves, per amount of cable pull. This "pull ratio" (not sure if my terminology is correct here) depends on the design of the derailleur. I think it's the same for Shimano 7, 8 and 9 speed setups, but not for 10+, but I could be wrong. The problem you could run into running a derailleur meant for significantly fewer cogs (e.g 5,6) on a larger cassette (besides any difference in pull ratio) is an overall range of motion that's too small, even with the limit screws all the way open.


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## slapheadmofo (Jun 9, 2006)

lyra said:


> Even though the shifter controls how much cable is pulled, the mechanical design of the derailleur determines how far the derailleur moves, per amount of cable pull. This "pull ratio" (not sure if my terminology is correct here) depends on the design of the derailleur. I think it's the same for Shimano 7, 8 and 9 speed setups, but not for 10+, but I could be wrong. The problem you could run into running a derailleur meant for significantly fewer cogs (e.g 5,6) on a larger cassette (besides any difference in pull ratio) is an overall range of motion that's too small, even with the limit screws all the way open.


You're right about the pull (actuation) ratio - the 7-8-9 Shimanos all use a 2-1 ratio, whereas the vast majority of SRAM/Gripshift use a 1-1 ratio. This ratio denotes how the amount of cable pulled by the shifter versus how much motion that 'pull' imparts to the derailleur (this is why you don't usually want to mix shifting components from different companies, though there are some lower end SRAM components that used the same actuation ratio as Shimano, just to keep everyone on their toes). You may well be right about the 5-6 speed stuff not having a sufficient range of motion to be able to reach each and every gear on the later stuff; can't say I've had to try it myself so no completely sure.

As far as 10-11 speed goes, I know nothing. I'm still running 8 speed Shimano (using a "9 speed" derailleur), as I found 9 speed set-ups finicky to keep in adjustment and prone to breaking chains.


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## AntonioLekic (Oct 25, 2013)

Thanks guys for your help will by my Shimano Deore Shadow.And i wont mix up the brands.Will put up pics of my finished bike when the dearurre.. comes.Thanks again.


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