cccorlew

Just what it say on the tin:
Is there a 28 tooth chainring for the Ultegra 6703 (10-speed) triple?

My Roubaix Expert Triple came with a 52-39-30 and I'd love it if it were just a bit lower. I really don't want to different cassette with wider gear spacing, so a lower small ring seems like my only option.

I've been told Shimano doesn't make this ring, and their weird bolt pattern means no one else does either. True or false?

If there is such a beast, where can i get it? Feel free to offer advice and warnings.

Thanks!

fietsbob

If the bolt circle is 74mm , yes. measure what you have,
or go to one of the many bike shops in the east bay
and they will tell you what fits.

FBinNY 

As said above, assuming the inner BCD = 74mm or (43.5mm from bolt to bolt on center) then there are smaller chainrings. Before buying, make sure that the FD has 3/16" (per 2 teeth reduction) under the chain to the closure on the cage.

The other consideration is offset, or the position of the teeth relative to the outer (toward middle chainring) face. This varies, with some lining up with the face, and others being inward (centered on the ring). This isn't hyper critical, but if the teeth are too far from the middle ring the chain can drop between them and jam, or bend the sprocket.

cccorlew

The distance between bolts looks to be about 55mm. This chart seems to say that's a XX BCD.
Does that make sense to you more knowledgeable folks?

IDIOT ALERT: See next message.

cccorlew

UPDATE:
Shimano Ultegra-6703 3x10sp Chainring 30 tooth 92BCD: For 6700 (130BCD), 6703 (92/130BCD), and 6750 (110BCD) Ultegra crank models. 6703, triple version uses a proprietary middle chainring that doubles as interface for small/inner chainring mounting. SIS compatible duraluminum construction.

Key Information

• part #: Y1LK30000
• speed: 3x10sp
• BCD: 92mm
• teeth: 30t (D)
• color: silver

Does that provide useful clues?

FBinNY 

You've got the ruler so you'd know better than we could.

However it's possible and one way you could cross check is by the distance from the outer edge of the bolt to the shoulder where the teeth begin. Every tooth adds about 3/32" or 4mm to the radius of a chainring.

A 74 BCD ring can take a 24t ring, while on a 94 the smallest is 29t. If you've only got 4mm room to shrink with a 30t, then then you need to look for a 94/29t sprocket (if it exists).

FBinNY 

There may be a workaround that will serve your needs.

various companies make 130bcd chainrings with built in triple adapters to convert doubles to triples. You might ignore the existing arrangement, treat your crank as a double and buy one of these adapter rings. Then you'll be free to use the granny of your choice.

Jeff Wills

Yep. You can't replace the inner ring with a 28 tooth because a 28-tooth chainring with that bolt pattern would run the chain through the inner chainring bolts.

However, If you replace the middle chainring with a Triplizer middle chainring: https://www.vintage-trek.com/tripleizer.htm . I think you can get a TA tripleizer from Peter White: https://www.peterwhitecycles.com/chainrings.asp (near the bottom of the page). With that installed you can go down to 24 teeth on the granny ring.

Chris_W

I actually tried this out on an Ultegra 6703 crankset a few weeks ago. I removed the stock middle and inner rings to see if a TA tripleizer with 42 teeth plus a 28 tooth inner ring would fit, and it did so without any problem. I didn't actually ride it on the road, I just wanted to check that it worked in principle, but I cannot see why it would not work OK in use.

The Dura Ace 7803 and 7703 triple cranks had the same arrangement, with the inner ring having a 92 mm BCD and mounted onto the middle ring instead of the spider. Shimano may have done this for weight saving, but I think that their main motivation was cost because it allowed them to use the same forging process to make the crank/spider assembly for double and triple cranks. With the 7703 they just had to provide a longer BB, and for the 7803 and 6703 they just have to attach a longer axle, and suddenly they had a triple without much extra manufacturing costs.

I always wonder if having the inner ring bolted to the middle in this way reduces the stiffness compared to being bolted directly to the spider. Since Shimano have used this on their top-end cranks, I guess there is not much difference, but now they are even using it on their new Ultegra-level tandem cranks - a pair of tandem riders can put a huge amount of torque on that inner ring when climbing a steep pitch, so I'm doubtful whether this is really an ideal setup.

IMO, the 6703 crank is the worst that Shimano have ever produced. All three rings are of a special design and it is a real problem if you want to change the size of any of them. A far better crankset is the 105 model, 5703, on which all three rings have a standard design and BCD. If you want to stick with the stock rings, then the 6703 is an excellent crank, but otherwise it is a big disappointment, and the 5703 is the best that is readily available (no, I don't consider any FSA crank to be a decent alternative to a Shimano).

AEO

yeah, 6703 crankset is a poor investment.
Imagine my disappointment when I bought it for the same price as a 5603.

however, the middle and outer rings can be swapped for regular 130BCD rings. It's just that it won't look as good.

Chris_W

If you swap the middle ring for a regular, non-tripleizer, ring then you no longer have a triple - you would then have a standard double with a poor chainline.

cccorlew

Thanks for this in depth report. It was really helpful. I guess I'm just generally out of luck with my dream of a 28 tooth chain ring, unless I pretty much want to start over.

I'm thinking that I'll get a Shimano Tiagra 12-30 cassette. That will give me the 1:1 I think need for a big double century with a ton of climbing. I know i won't miss the 52-11 gear. The Tiagra weighs more than the Ultegra, and more importantly lacks the cool factor, but really, who will notice other than me? And as a bonus almost all the middle gears remain the same.

Chris_W

Alternatively, you can assemble a 12-30 cassette that weighs 244 grams by combining most of a Dura Ace 12-27 cassette (minus the 16 tooth cog) with the individual 30 tooth cog from the Tiagra 12-30 cassette, plus a couple of well-chosen spacers in between. See my complete post on how I did this here. But if you don't want the extra expense then the complete Tiagra 12-30 works very well.

cccorlew

Here's my latest blog post that doesn't really clear up things.... yet.
https://ccorlew.blogspot.com/2012/03/fight-fight.html

Here's the best part: I'm looking at a serious double with a lot of climbing, so what does the box say?

Insulting gear box by ccorlew, on Flickr

davidad

I hate all the new and improved stuff that doesn't help us. This set will allow you to put a 24 on the inner ring. https://www.bikeparts.com/search_resu...p?ID=BPC375353

Camilo

I didn't read the thread really, really carefully, so excuse me if I missed something.

My wife has a standard Shimano triple crank. Now, hers is 9 speed, but my solution to get her lower gears using a MTB cassette and RD still might work for you as an alternative to messing with codging together new chain rings. Her system works flawlessly.

I happened to have a pre-10 speed Deore RD on hand (I don't know if it was originally on an 8 or 9 speed MTB), and her stuff is 9 speed which is very easy and relatively cheap to deal with, I understand you can do the same thing with Shimano 10 speed MTB cassettes. I've heard that you need to find a 9 speed MTB RD to use with the 10 speed road shifters and 10 speed MTB cassette, as the 10 speed MTB RD isn't perfectly compatable for some reason. This would actually be a good thing because the 9 speed RD would be cheaper anyway and probably is the same as an 8 speed too? You would have to check that out. There's been threads on this in bikeforums.net and roadbikereview.com.

Another solution I've heard - depending on what cassette you already have and how many lower gears you need - is that some 28 or even 32 tooth cassettes can be made to work with Shimano long cage road derailleurs. I guess it depends on exactly how the derailleur hanger is designed and can vary from frame to frame.