Derailleur Question

[msl819]

Looks like I need to replace my rear mech. I am looking to go from a 12-25 to 12-27. This will be Ultegra 6600, will I need a short, med, or long cage derailleur? And why? Thanks guys.

[dave thompson]

Looks like I need to replace my rear mech. I am looking to go from a 12-25 to 12-27. This will be Ultegra 6600, will I need a short, med, or long cage derailleur? And why? Thanks guys.

If you're running a triple crank you will have to use the long cage rear der. Otherwise a short cage will work if you run a double crankset. The long cage is necessary to take up the extra chain length with the triple set up.

A Shimano 5600, 6600 or 7800 derailleur will work fine.

[msl819]

Sweet... so what is the purpose of the mid cage?

[cnighbor1]

Looks like I need to replace my rear mech. I am looking to go from a 12-25 to 12-27. This will be Ultegra 6600, will I need a short, med, or long cage derailleur? And why? Thanks guys.

Look at shimano MTB Rd's has they are compatable and you can run a 32T cog for bail out hills

[dave thompson]

Sweet... so what is the purpose of the mid cage?

Shimano only makes two road cage lengths, short and long, though sometimes the long is referred to as a mid-cage because it's not as long as a Shimano MTB long cage derailleur, which is quite long to use with smaller inner rings and large 34~36t cassettes found on mountain bikes.

[msl819]

Thanks guys!

[xjoex]

You won't need a long cage on a 27T either, in my experience.

-Joe

[Ralph]

Don't see why short cage wouldn't work fine.

[Chance]

Looks like I need to replace my rear mech. I am looking to go from a 12-25 to 12-27. This will be Ultegra 6600, will I need a short, med, or long cage derailleur? And why? Thanks guys.

Depends.

As other have stated, Shimano only made the 6600 rear derailleur in short and long. Either can handle the 27-tooth large cog so that is not a limiting factor.

However, if you want to follow Shimano specifications to the letter (which many often claim is not necessary), it depends on what rings you are using up front. The 6600-SS has a maximum rated capacity of 29 teeth and the 6600-GS a maximum capacity of 37 teeth. So for your 12-27 cassette (which requires 15 teeth of capacity) you should be OK with the short cage derailleur as long as the rings don't exceed 14 teeth of difference. Hence 53-39 rings fall within specifications. If you are using some sort of oddball ring combination (like 50-33 or 52-34 compact) it may exceed the short cage derailleur's total capacity. And as mentioned above by others, most triples will also exceed the short-cage rear-derailleur's total capacity.

Often you can exceed RD ratings without problems, but it shouldn't be viewed as a given.

[oldpotatoe]

Looks like I need to replace my rear mech. I am looking to go from a 12-25 to 12-27. This will be Ultegra 6600, will I need a short, med, or long cage derailleur? And why? Thanks guys.

Short will work fine if you have a double crank. 'Medium', road triple 6603 if you have a triple crank.

So you have enough chain for big-big combo