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MTB Rider
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Digital cycling ...

wiebs6 said:
I use shimano parts and was wanting a new rear derailleur and i have an 8 speed.
Does a 9 speed deraileur work for my 8 speed drivetrain?
Derailleurs are effectively analog mechanisms. If you pull the cable 1mm the derailleur will move 1mm (at least on SRAM it does). It is the SHIFTER that determines compatibility with the cassette.

8 speed cassettes are mated to 8 speed index shifters.
9 speed cassettes are mated to 9 speed index shifters.

SRAM X-series shifters must be used with SRAM X-Series derailleurs.
Shimano Rapid Rise Derailleurs should be paired with a Rapid Rise Shifter (otherwise it will work backwards).

There is a reprieve. Front derailleurs are pretty much universal as are chainrings.
 

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Time is not a road.
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A buddy told me he was having trouble with an XTR derailleur and an 8 spd chain, noting that the width of the der. was too narrow for the 8 spd. Anyone noticed this issue?
 

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Yes, I forgot that ...

chad1433 said:
A buddy told me he was having trouble with an XTR derailleur and an 8 spd chain, noting that the width of the der. was too narrow for the 8 spd. Anyone noticed this issue?
The problem you cite is not the derailleur. The derailleur is designed to move between two points, the size of the cassette. 8 and nine speed cassettes are EXACTLY the same widtch. A nine speed cassette squeezes in one more cog so the spacers between each cog is thinner (as well as the cogs themseles). Hence the 9 speed chain is thinner because it must fit in tighter gaps.

8 speed chains are mated to 8 speed cassettes.
9 speed chains are mated to 9 speed cassettes.

It doesn't matter what brand. What matter is the thickness of the chain. An 8 speed chain is too big for a 9 speed cassette. Shimano chains will work just fine with SRAM cassettes and vice-versa.
 

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I'm running

8 Speed, and have a few 9 speed rear mechs. They're all working without any problems of the chain being too wide. Actually measured some of the first 9 speed rear mechs with a set of calipers to make sure there were not going to be any problems. Think it was around 1/2 of 1mm closer on one rear mech, and 1/2 of 1 mm wider on another.

You'll be fine.

JmZ

chad1433 said:
I'm referring to the width not of the indexing between the cogs, but between the pulleys on the der. itself where the chain feeds through.
 

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'18 Transition Sentinel
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only shifter/casssette/chain

My wife's old low-end Trek has sub-Deore ("Acera"?) 8x3 stuff.
So, to make it 9x3, all I need is new 9-spd shifters & 9-spd cassette (& 9-spd chain), right? ("Right...")
 

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9 speed derailleur, too

PiroChu said:
My wife's old low-end Trek has sub-Deore ("Acera"?) 8x3 stuff.
So, to make it 9x3, all I need is new 9-spd shifters & 9-spd cassette (& 9-spd chain), right? ("Right...")
You'll need a 9 speed rear derailleur, too. A 9 speed r/d can be used with 8 speed shifters and cassette, but not the other way around.

Clyde
 

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Call_me_Clyde said:
You'll need a 9 speed rear derailleur, too. A 9 speed r/d can be used with 8 speed shifters and cassette, but not the other way around.
Hummm.... I thought I read above that the shifter dictates the "8spd vs 9spd", while the rear-drlr (LX) - being 8spd & 9spd compatible(?) - will act accordingly. Did I completely misunderstand something?
 

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(enter witty phrase here)
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PiroChu said:
My wife's old low-end Trek has sub-Deore ("Acera"?) 8x3 stuff.
So, to make it 9x3, all I need is new 9-spd shifters & 9-spd cassette (& 9-spd chain), right? ("Right...")
Possibly. If the rear wheel uses a freehub, then you can swap out the cassette. Some older (or cheaper) bikes use freewheels. If yours does, you'll need a new wheel.

Also, the derailleurs might work. Might not. The shifting could be a little unresponsive with the narrower 9sp chain. Especially with Acera.

Why are you upgrading? Stuff broken or worn out? Or just for the sake of it?
 

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tlg said:
Why are you upgrading? Stuff broken or worn out?
Well, the sub-Deore 8-spd shifters on my wife's old Trek (probably of '98/'99-ish?) is loosing its ratchet "bites" (slipping), and I have some old LX 9-spd shifters lying around in my garage, so I'd figured I'll use those (instead of paying retail for some brandnew low-end 8-spd shifters), and convert it to 9spd while at it, since her bike could probably use a new chain/cassette anyway. (Also, then I just have to stock/maintain 9spd stuff handy, not both "8spd for her" & "9spd for me".)

Do you guys think it make sense to do that, or should I just pay retail for new 8spd shifters?

Just to clerify... I think everything on her bike is sub-Deore (Acera?), except for her rear drlr, which is a LX. I also think that luckily her cassette will come off her rear wheel, if I recall correctly (though I have to take a closer look later - I haven't closely checked out her bike in a very long time, as you can tell).

What do you guys think?
- PiroChu
 

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PiroChu said:
Well, the sub-Deore 8-spd shifters on my wife's old Trek (probably of '98/'99-ish?) is loosing its ratchet "bites" (slipping), and I have some old LX 9-spd shifters lying around in my garage, so I'd figured I'll use those (instead of paying retail for some brandnew low-end 8-spd shifters), and convert it to 9spd while at it, since her bike could probably use a new chain/cassette anyway. (Also, then I just have to stock/maintain 9spd stuff handy, not both "8spd for her" & "9spd for me".)

Do you guys think it make sense to do that, or should I just pay retail for new 8spd shifters?
In that case, it's a 50/50 call. It's always great to reuse leftover parts.

Also consider, new low end technology is sometimes better than old "high end" technology. It trickles down over the years.

Something else I just thought of. If you replace the cassette and chain, you really should replace the crankset or chainrings. You crank may not work with 9sp. And even if it does, putting a new cassette/chain on worn chainrings will cause problems.
 
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