Bicycle Mechanics - 12-32 or 11-34 require longer derailleur???

Can I use a standard long-cage ultegra or dura ace rear 9 derailleur with a 12-32 or 11-34 casette? Or do I have to go to a mountain bike derailleur (Deore XT) or such?

Can I use a standard long-cage ultegra or dura ace rear 9 derailleur with a 12-32 or 11-34 casette? Or do I have to go to a mountain bike derailleur (Deore XT) or such?

Yes, you'll need a mtb RD with anything over a 30t large cog-

Can I use a standard long-cage ultegra or dura ace rear 9 derailleur with a 12-32 or 11-34 casette? Or do I have to go to a mountain bike derailleur (Deore XT) or such?http://www.bikeforums.net/images/editor/menupop.gif
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Yes, you'll need a mtb RD with anything over a 30t large cog-

I think the limits on long cage road derailers are very conservative. Shimano says that they will only handle a 27 tooth low which happens to be the same limit as a short cage derailer. I know from experience that a short cage will handle more than that (I shoe horned in a 29 once that worked just fine). Before buying a new derailer I'd be tempted to see what you can do with your existing derailer. Changing cassettes is a piece of cake and if it works, you won't have to buy a new derailer. If it doesn't...well you'll be out a few minutes for the experiment;)

I think the limits on long cage road derailers are very conservative. Shimano says that they will only handle a 27 tooth low which happens to be the same limit as a short cage derailer. I know from experience that a short cage will handle more than that (I shoe horned in a 29 once that worked just fine). Before buying a new derailer I'd be tempted to see what you can do with your existing derailer. Changing cassettes is a piece of cake and if it works, you won't have to buy a new derailer. If it doesn't...well you'll be out a few minutes for the experiment;)


What does the cage length have to do with the large cog capacity? (answer: nothing). I understand that the 27t large cog rating is conservative, but the 30t limit I mentioned is beyond that. 32t and 34t are mtb RD territory-

Longer? No. Derailleur with bigger large-cog capacity? Yes.

These properties are not interchangeable. You will most likely need a "MTB" RD, and such a beast will most likely be long-cage. But it is not its long-cagedness that brings about the ability to handle a larger cog; it is the length of the parallelogram.

The RD needs to be able to clear the largest cog, so the pulleys don't rub. If a short-cage "road" (Ultegra/DuraAce) RD doesn't work, than a long-cage road RD won't either.

What does the cage length have to do with the large cog capacity? (answer: nothing). I understand that the 27t large cog rating is conservative, but the 30t limit I mentioned is beyond that. 32t and 34t are mtb RD territory-

I would bet that it could be made to work. The 27 tooth large cog is way conservative. Like I said, it's worth trying it before purchasing a new derailer. I'd probably stick with the 32 just to be on the safe side. If the jockey pulley rubs, you might be able to adjust the B-screw to get where you need it.

If it doesn't work, what is wpaul10 out? A little time.

I have an XT long cage RD and even that just barely clears the 34T sprocket on my bike. And only after I gave it a B-angle screw more than twice as long as the original.

I have ran a Tiagra RD on a 32 with no ill effects.

I have ran a Tiagra RD on a 32 with no ill effects.

I have ran a Tiagra RD on a 32 with no ill effects.
Ability of a RD to handle large cogs depends not only on the type of this particular RD, but also on the shape and length of the derailer hanger. A Tiagra RD on one of my bikes just barely clears the 30T cog with B-tension screw turned to the max; it surely won't handle a larger one.