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Road Cassette + MTB Derailleur = Huh?

Dirt Jumper

Chimp
Sep 6, 2005
87
0
Colorado Springs, CO
I stroll into my local bike shop, aiming to get a road cassette, because often when I'm even riding around, I'm in the 16t-18t cogs in the back, and I rarely use the largest cog.

So I go to the cassettes area, look at the SRAM 9-spd road cassettes, and I find one and ask a clerk if he's tried it and if it's a good 'un, and he just says, "Wait, you have a mountain bike right?"
I'm just like, "Uhh, yeah, you know, my DB Assault." and he goes,
"Well, with the MTB derailleur, it's just gonna be... funky..." I look at him, and he says,
"Well, just because they aren't meant to be used together. That's why Shimano and SRAM make road cassettes, and they make MTB cassettes."

SO, I just walked out of there, angry, because I got the feeling that if I bought it, they wouldn't put it on for me because of my crazy oblivious stupidity towards running a road cassette with a MTB derailleur.

Is it really that bad to run a road cassette with an MTB derailleur (SRAM X.7)?
 

Wumpus

makes avatars better
Dec 25, 2003
8,164
154
Six Shooter Junction
The spacing on the cassettes is the same -- road vs. mtn. The only problem might be chain slack if you are running a long cage derailer, but it isn't that big a problem. My crossbike has a 12-25 dura ace cassette with a long cage XT derailer, and I haven't had any issues.
 

Muuqi

Monkey
Oct 11, 2005
252
0
Ashland Oregon
I've got a sram road cassette on my jumping bike and run a sram derailler and it works perfectly. That guy didn't know what he was talking about. 9 speed spacing is 9 speed spacing, period.
 

Wumpus

makes avatars better
Dec 25, 2003
8,164
154
Six Shooter Junction
Muuqi said:
I've got a sram road cassette on my jumping bike and run a sram derailler and it works perfectly. That guy didn't know what he was talking about. 9 speed spacing is 9 speed spacing, period.
Unless it is campy.
 

Arsbars

"Finger Lickin' Good"
Mar 25, 2003
551
0
Charlotte, NC
The actual issue comes with the front shifting not the rear. Because of the chain length when shifting down you may find that you drop your chain into the frame. I haven't experienced it with a triple - but I know on a road bike if you have a double with a long cage derail in the back you tend to drop your chain a bunch if the limit screws are set up correctly. Give it a try, the worse that will happen is you drop your chain, or you need to cut back a couple links.

Let me know if that makes sense. If not I'll try to draw up a diagram!
 

BMXman

I wish I was Canadian
Sep 8, 2001
13,854
0
Victoria, BC
[rant ]Yeah support your LBS...it's full of idiots who don't have a clue WTF they're talking about![/rant]

Seriously though it's amazing how much mis-information is out there concering bikes...D