signalnc

I have a 2006 Ultegra group on my bike (except the cranks). I think it's Ultegra 6600. I have Truativ carbon cranks . The cranks are 53/39 and i have an 11-23 cassette. I would like to change the gearing. I was told the 6600 ultegra can only take a 27t cog not a 28. Is this true? what about changing thr chainrings. Can i swap out the 53/39 to a 50/34? thanks

joejack951

A 28T large rear cog will most likely work fine with your current set up. I can't guarantee it but I'm currently using a 27T large cog with my 6600 rear derailler and it clears just fine.

As for the chainrings, the only way you can make a significant chainring change is to get a different crankset. Your 53/39 double almost certainly uses a 130mm BCD for the chainrings (measure to be sure though as there are 110mm BCD 53/39 chainring cranks). The smallest inner chainring you can mount on a 130mm BCD is a 38T. Not worth the effort. To mount a 34T chainring, you'll need a crankset with a 110mm BCD (otherwise known as a compact crank). Depending on how much lower gearing you are looking for, you can change the crank or cassette or both. The cassette is by far the cheapest and easiest swap though so I'd suggest starting there.

Zouf

joejack951 is correct as far as 39-38 being the lower limit on 130 BCD - and 38T can be a problem, you have to make sure the chain will clear the crank spider. However, there are indeed options on the large chainring, FSA has 50T 130 BCD chainrings that work great with Ultegra. It all depends on what your motivations for gearing changes are (want to spin faster and be more centered on the cassette? want to climb steep hills?), and what your budget is (compact crank replacement ok for you?). I swapped my 53/39 Ultegra rings for 50/39 FSA because the chainrings were dead and needed replacing anyway, and I,m more of a spinner than a masher - but that's me, your mileage may vary.

signalnc

thanks for the replies. My motivation is to get an easier gear for climbing. My current setup is fine for hills with max 6% gradient and nothing longer than 1 mile where I am riding now. Changing to a compact crank is not out of the question. I am going to replace the cassette to either a 12-25 or a 12-27. If I get the 12-25 I may change to a compact next year before heading to the Blue ridge mountains. I am just a casual rider (2 or 3 times a week--1000 to 1500 miles a year). Thanks again

woodway

I am running 50-34 on the front and 12-30 on the rear with my Ultegra 6600 deraileur. That's 16+18=34 teeth on a derailluer rated for 27 teeth. Works fine, shifts fine and has done so for the last 8000 miles. I am sure that you'll have no problem going from 27 to 28 teeth on your setup. the derailuers are spec'ed somewhat conservatively.

JiveTurkey

Hold on a sec, you are describing two things.

"34 teeth" refers to the total capacity: [50+30]-[34+12]=34. The 6600-SS RD is rated at 29T or less and the 6600-GS RD is rated at 37T or less. If you are using the SS (short cage) RD, then, yes, you are exceeding recommended chain wrap capacity of 29T (not 27T).

OP: The major problem with exceeding total capacity with a double crank is that even though you should never actually use the large-large combo, the chain should be long enough to go there, but if this is the case, then the smaller cogs of the cassette won't run as well while using the inner chainring because the RD won't be able to take up all the slack in the chain.

The other limitation of an RD is largest cog. All 6600 RDs are rated at 27T or less. However, most people can get a 28T to work, and some can get a 30T to work by screwing in the b-tension screw.

https://techdocs.shimano.com/media/te...9830616226.pdf

DMF 

You sure it's not a 9-speed group (6500)?

12-27 will make a big difference and work with anything in the Ultegra lineup. But if you go to a compact you may want a long-cage road RD.