# Ultegra Di2: How low can it go?



## wgscott (Jul 14, 2013)

I've borrowed a trek domane 5.2 with Ultegra, 50/34 (compact crank) and 11-28 cassette in order to test to see if I can handle the gearing where I live (Santa Cruz CA mountains). This is my first time on a road bike and first time in SPDs in over a year, since a nasty ankle break. So far I have been pleasantly surprised (going downhill seems more of a challenge), but am curious what restrictions Di2 ultegra would place on gearing if I were to get it. So how low can it go?


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## wgscott (Jul 14, 2013)

I think I might have found the answer to my own question, on the Shimano website, of all places:

Front:

Model Number	FD-6870
Series	ULTEGRA
FD Model Number
Cassette Compatibility
Top Gear Teeth	46-53T
Maximum Capacity	16T

*Rear:*

Model Number	RD-6870
Series	ULTEGRA
Cassette Compatibility	11-speed
Maximum Sprocket	low: 28T, top:12T
Minimum Sprocket	low: 23T, top:11T
Maximum Front Difference	16T
Total Capacity	33T

I'm guessing what this means is that the front could be a 46/30 (if they offer that) and the rear 12-28 (not clear on the 33T total capacity thing)


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## NoahD (Jan 21, 2003)

34 is the smallest chainring you can put on a 110 bcd crank (which is most likely what you have). You can run a rear cassette with a 28 "maximum sprocket". Those are low gears but you might want more on Alba or Mt Charlie or Jamison (I used to live in SC)


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## wgscott (Jul 14, 2013)

I don't have one yet; I'm going to have a bike built. (I live in Bonny Doon but I'm scared even to drive on those roads.)


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## DrSmile (Jul 22, 2006)

33T refers to the chain take-up limit, meaning that the front and rear differences from largest to smallest cog/ring add up to 33 teeth or less. So if you have 50/34 front rings you could run an 11-28 cassette. Looking at the other limits listed though I can't quite figure out how you could ever exceed 33 teeth, so it's kind of pointless.


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## ultimobici (Jul 16, 2005)

Ultegra Di2 has two rear mechs, SS & GS. The SS is the one you have found specs for, the GS is designed for larger range cassettes and goes to 32T max with a 37T capacity
Product
SO in fact you'd be able to go with a 50/34 mated to an 11-32 cassette with no issues at all. Whether you'll actually need that is down to your fitness levels though!


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## MJCBH (Nov 25, 2002)

I Just had my bike built up with Di2 (10sp) and run a 50/34 with a 30T cassette no problem. I believe I have the SS rear mech but I could be wrong there (my mechanic said that 30T was the highest I could go there or I would have put a 32tooth on). It's a great group!


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## r1lee (Jul 22, 2012)

If you get the 6870 mid length cage rear derailleur you can go 32t in the rear.

Gs derailleur 

Bike24 - Shimano Ultegra Di2 RD-6870-GS Rear Derailleur 2x11 - medium


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## wgscott (Jul 14, 2013)

ultimobici said:


> Ultegra Di2 has two rear mechs, SS & GS. The SS is the one you have found specs for, the GS is designed for larger range cassettes and goes to 32T max with a 37T capacity
> Product
> SO in fact you'd be able to go with a 50/34 mated to an 11-32 cassette with no issues at all. Whether you'll actually need that is down to your fitness levels though!


Thanks, I missed that other one completely. That could really help.

Too fat, too old, ankle break ... yeah, I guess I have some fitness challenges. :blush2:


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## wgscott (Jul 14, 2013)

ultimobici said:


> Ultegra Di2 has two rear mechs, SS & GS. The SS is the one you have found specs for, the GS is designed for larger range cassettes and goes to 32T max with a 37T capacity
> Product


Oddly enough, only the SS is listed on the American site. The EU site has both.


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## ericm979 (Jun 26, 2005)

You can very probably run a 30t cog on the short cage derailleur. Your frame would have to have an unusually short deraillur hanger for it to not work. I've done it with 7700, 7800, 7900 and Sram derailleurs. With 7900 and newer Shimano slightly increased both the cog capacity and the wrap vs the older derailleurs.

Most 110mm BCD "compact" cranks can take a 33t ring. Some have unusually long mounting tabs which interfere with the chain side plates. You can get 33t rings from Harris Cyclery.

I ride the SC mountains as well. We have a lot of steep stuff here. I'm very fit, climb well and I run a 50/34 and 12-27, 11-26 or 11-28 cassettes. xx-30 for some special extra hard events.

Shimano makes a nice 12-30 cassette.


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