Using a road derailleur on an mtb cassette

east coast · 11-08-2006, 08:55 PM

I want to run an old 8 speed Dura Ace rear der w/ 8 speed xt shifters and a 28t rear cassette. Will it work? What's the largest cassette ring that can be used?

stuart@nsmb.com · 11-08-2006, 09:30 PM

Shimano on Shimano is fine. Largest cog size should be stamped on the cage of the derailleur. 28T might be too big if it's a short cage (think 27T is the max on some).

connor · 11-08-2006, 09:57 PM

yeah I used to run a short cage 105 der, 9spd with a road cassette. you might be able to find yours in the charts below if you know the model.

http://bike.shimano.com/publish/cont...atibility.html

east coast · 11-08-2006, 10:07 PM

Quote:

Originally Posted by connor

yeah I used to run a short cage 105 der, 9spd with a road cassette. you might be able to find yours in the charts below if you know the model.

http://bike.shimano.com/publish/cont...atibility.html

I looked but the chart only has new products on it and I'm looking for Dura Ace 8 speed which is quite a few years old by now. I did find this Forum though and the last post on it gives me hope:

http://www.bikeforums.net/archive/index.php/t-2497

Timmigrant · 11-09-2006, 01:34 AM

I've run short cage 105 derailuers on 32 rear rings. You just have to turn the A-Knuckle adjustment screw in significantly to prevent the top jockey wheel riding on the 32 tooth ring teeth. You should be more than fine with a 28th cassette.

Dantes Inferno · 11-09-2006, 01:57 AM

I use a Shimano XT derailer with a 105 road cage bolted onto it. Its the absolute bomb. Works on any shimano cassette. (i also ride 8 speed). You may find a problem entering the big ring.

zahgurim · 11-09-2006, 06:15 AM

It's usually fine to run a roady der on mtb, as long as you aren't getting too much chain growth on a dually setup, stretching the short cage out.

I run roady der's on my bikes. One with an 11-32, one with an 11-34. I did change the top jockey wheels though, from 11 tooth to ten tooth to give me a bit more room.
You wanting to run an 11-28 should be no problem at all.

The maximum cassette tooth reccomendation by Shimano on their road der's is bunksauce when on a mtb, as the der mount on a roady is closer to the cassette than on a mtb. Read: mtb has more room, allowing for a larger cassette.
The only thing to watch for is that you don't stretch the cage out while going through your travel. Single ring in front is good on a long-travel fully.

sanrensho · 11-09-2006, 06:23 AM

Note that the RD-7402 Dura Ace 8-speed derailleur uses a non-standard throw ratio (indexing). It's supposed to work with a 9-speed shifter--shifts 8 speeds with one extra click.

east coast · 11-09-2006, 01:30 PM

Quote:

Originally Posted by sanrensho

Note that the RD-7402 Dura Ace 8-speed derailleur uses a non-standard throw ratio (indexing). It's supposed to work with a 9-speed shifter--shifts 8 speeds with one extra click.

How does that work? Aren't 8 speed chains slightly wider than 9? Wouldn't that mean the cassettes are spaced a little more too? And if that's where the term "non-standard throw ratio" comes in then how can it work w/ a standard 8 speed shifter as well?

east coast · 11-09-2006, 01:54 PM

Quote:

Originally Posted by zahgurim

It's usually fine to run a roady der on mtb, as long as you aren't getting too much chain growth on a dually setup, stretching the short cage out.

I run roady der's on my bikes. One with an 11-32, one with an 11-34. I did change the top jockey wheels though, from 11 tooth to ten tooth to give me a bit more room.
You wanting to run an 11-28 should be no problem at all.

The maximum cassette tooth reccomendation by Shimano on their road der's is bunksauce when on a mtb, as the der mount on a roady is closer to the cassette than on a mtb. Read: mtb has more room, allowing for a larger cassette.
The only thing to watch for is that you don't stretch the cage out while going through your travel. Single ring in front is good on a long-travel fully.

I'll be running the DA der on my Bullit. Single pivots do stretch the chain so I'll just have to make sure I leave an extra link in I guess...

Dantes Inferno · 11-09-2006, 04:06 PM

my bullit was fine with a roady der.

xy9ine · 11-09-2006, 05:17 PM

Quote:

Originally Posted by east coast

I'll be running the DA der on my Bullit. Single pivots do stretch the chain so I'll just have to make sure I leave an extra link in I guess...

its a good idea to check your chain length at max travel (ie, pull the shock spring & fully compress the suspension while in the big cog). there's nothing worse than ripping off a shiny new d/a on your first ride.

sanrensho · 11-09-2006, 07:17 PM

Quote:

Originally Posted by east coast

How does that work? Aren't 8 speed chains slightly wider than 9? Wouldn't that mean the cassettes are spaced a little more too? And if that's where the term "non-standard throw ratio" comes in then how can it work w/ a standard 8 speed shifter as well?

Has nothing to do with the chain width or cassette spacing. The 8-speed Dura Ace shifter/derailleur uses a different amount of cable pull to accomplish the same throw as a standard 8-speed setup.

To summarize:

RD-7402 + Dura Ace shifters + standard 8-spd cassette = Works

RD-7402 + standard 9-spd shifter + standard 8-spd cassette = Works (with one extra click)

RD-7402 + standard 8-speed shifter + standard 8-speed cassette = No worky

By standard, I mean "Shimano or Shimano-compatible." If you really want to know more about DA 8-speed, read here:

http://www.sheldonbrown.com/dura-ace.html

east coast · 11-09-2006, 08:04 PM

Quote:

Originally Posted by sanrensho

Has nothing to do with the chain width or cassette spacing. The 8-speed Dura Ace shifter/derailleur uses a different amount of cable pull to accomplish the same throw as a standard 8-speed setup.

To summarize:

RD-7402 + Dura Ace shifters + standard 8-spd cassette = Works

RD-7402 + standard 9-spd shifter + standard 8-spd cassette = Works (with one extra click)

RD-7402 + standard 8-speed shifter + standard 8-speed cassette = No worky

By standard, I mean "Shimano or Shimano-compatible." If you really want to know more about DA 8-speed, read here:

http://www.sheldonbrown.com/dura-ace.html

So I'm out of luck trying to run a 8 speed LX shifter with a RD-7402 and 8 speed mtb cassette? I must be reading the chart wrong but I don't see where it says that.

east coast · 11-09-2006, 08:08 PM

Quote:

Originally Posted by sanrensho

Has nothing to do with the chain width or cassette spacing. The 8-speed Dura Ace shifter/derailleur uses a different amount of cable pull to accomplish the same throw as a standard 8-speed setup.

To summarize:

RD-7402 + Dura Ace shifters + standard 8-spd cassette = Works

RD-7402 + standard 9-spd shifter + standard 8-spd cassette = Works (with one extra click)

RD-7402 + standard 8-speed shifter + standard 8-speed cassette = No worky

By standard, I mean "Shimano or Shimano-compatible." If you really want to know more about DA 8-speed, read here:

http://www.sheldonbrown.com/dura-ace.html

From what I read of the Sheldon Brown article it depends on what year RD-7402 I'm using...

11-08-2006, 08:55 PM	#1
east coast Registered User Join Date: Jun 2003 Location: connecticut Posts: 433 Rep Power: 3421	Using a road derailleur on an mtb cassette I want to run an old 8 speed Dura Ace rear der w/ 8 speed xt shifters and a 28t rear cassette. Will it work? What's the largest cassette ring that can be used?

11-08-2006, 09:30 PM	#2
stuart@nsmb.com Writer/editor/photo taker Join Date: Dec 2002 Location: In transit Posts: 2,109 Rep Power: 6818	Shimano on Shimano is fine. Largest cog size should be stamped on the cage of the derailleur. 28T might be too big if it's a short cage (think 27T is the max on some). __________________ ************************************* She said, why don't you stop your crying/ Go outside and ride your bike - Sliver, Nirvana "If stars were all that mattered, why would I go to the trouble of writing a review?" - Roger Ebert

11-09-2006, 01:34 AM	#5
Timmigrant Registered User Join Date: Jan 2004 Location: Burnaby Posts: 2,396 Rep Power: 178443	I've run short cage 105 derailuers on 32 rear rings. You just have to turn the A-Knuckle adjustment screw in significantly to prevent the top jockey wheel riding on the 32 tooth ring teeth. You should be more than fine with a 28th cassette. __________________ Biking: As addictive as cocaine, twice as expensive! My Super Interesting Website -

11-09-2006, 01:57 AM	#6
Dantes Inferno Freetard Ricing Join Date: Dec 2004 Location: East Van Posts: 8,567 Rep Power: 2584421	I use a Shimano XT derailer with a 105 road cage bolted onto it. Its the absolute bomb. Works on any shimano cassette. (i also ride 8 speed). You may find a problem entering the big ring. __________________

11-09-2006, 06:15 AM	#7
zahgurim ≈ > ♥ Join Date: Oct 2005 Location: Away from the Valley; lol Asia Posts: 3,864 Rep Power: 13880243	It's usually fine to run a roady der on mtb, as long as you aren't getting too much chain growth on a dually setup, stretching the short cage out. I run roady der's on my bikes. One with an 11-32, one with an 11-34. I did change the top jockey wheels though, from 11 tooth to ten tooth to give me a bit more room. You wanting to run an 11-28 should be no problem at all. The maximum cassette tooth reccomendation by Shimano on their road der's is bunksauce when on a mtb, as the der mount on a roady is closer to the cassette than on a mtb. Read: mtb has more room, allowing for a larger cassette. The only thing to watch for is that you don't stretch the cage out while going through your travel. Single ring in front is good on a long-travel fully. __________________ The best things in life all start with the letter B Hooray for: Bacon, Bikeys, Boobies, Boards, and Beer!

11-09-2006, 06:23 AM	#8
sanrensho Registered User Join Date: Jun 2003 Location: NV Posts: 7,137 Rep Power: 592698	Note that the RD-7402 Dura Ace 8-speed derailleur uses a non-standard throw ratio (indexing). It's supposed to work with a 9-speed shifter--shifts 8 speeds with one extra click. __________________ "The song of a bird...We used to ask Ennesson to do bird calls. He could do them. How he could do them, and when he perished, along with him went all those birds..."-Return from the Stars, Stanislaw Lem "We just walk around, and sometimes we go out and dance, and then we listen to the environment."-Ralf Hutter, Kraftwerk

11-09-2006, 04:06 PM	#11
Dantes Inferno Freetard Ricing Join Date: Dec 2004 Location: East Van Posts: 8,567 Rep Power: 2584421	my bullit was fine with a roady der. __________________

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