My bike has full ultegra components - brakes, FD, RD, triple hollowtech chainring and a 12-15 CS6600 cassette.

I know that Shimano's official line is to not go any lower than a 27 but recent forum users have suggested that this is just Shimano being conservative and that the rear derailleur could probably handle a 29T sprocket. Indeed, given that I never cross-chain I wouldn't have to worry about getting a new chain to cope with 52x29. I simply wouldn't use that ratio.

But since Shimano don't manufacture a sprocket any lower than 27T, what cassettes are available on the market that would allow me to get a 30x29 gear? I'm obviously looking for something that would not cause shifting problems with Ultegra components.

Many thanks

Sorry fot the typo error - of course, I meant to say that I currently have a 12-25 ten speed and not a 12-15!!!

As suggested earlier, why not just swap the 30T inner ring for a 28T? A 28/27 is the same as a 30/29. Later, as 10 speed moves down market, Shimano will make cassettes with bigger cogs,as they abandon the "racer only" market.

__________________
Richard
Ozark Bicycle Service
http://www.ozarkbicycleservice.com

Biggest I know of is IRD's 12-28 cassette. But that's $119, and still not low enough. I would go with Ozark's suggestion. It's going to be a lot cheaper.

I have a 26 tooth TA inner chainring for a 10 speed triple, it was US$29.95 from Harris Cyclery. You want to buy it?

__________________
Cheers,
George.

I was under the (perhaps wrong) impression that the front derailleur could only cope with a maximum teeth differential of 22 (ie, 52 to a 30 equals 22 teeth). Swapping to a 28 tooth inner ring would be a differential of 24 and I'm sure I read somewhere (probably on this forum) that this would cause FD shifting issues.

It should work.

Put the FD on the small chain ring.
Run the RD through the range and obseve the clearance between the chain and the flat horizontal portion of the FD cage, at the back of the FD.

Measure the clearance at the middle sprocket and the largest sprocket. This will give you an idea of how much smalller the small chain ring can be before the chain fowls the FD cage.

The seatpost angle has an effect here as well. (Don't you just miss Mr B when you really need him?)

__________________
Cheers,
George.

FD "capacity" is, like RD max cog size, a very conservative spec. You can use a 28T with your FD; I've done it on several STI triples. As an aside, all STI triples require careful set-up for proper function, but a 28T works as well as 30T.

__________________
Richard
Ozark Bicycle Service
http://www.ozarkbicycleservice.com

Gotta disagree here: the clearance at the back of the cage is only a factor if one wants to use the inner ring with the middle and outer rear cogs. Why would you want to do that? As soon as you can have the same gear on the middle ring, it's time to get out of the inner ring. As long as the inner works with the 2 or 3 largest, innermost cogs, all is well. Those are your climbing gears. (And, BTW, if the chain does rub on the rear of the cage, the rattle is a good reminder that it's time to out of the granny ring!)

__________________
Richard
Ozark Bicycle Service
http://www.ozarkbicycleservice.com

Lean to read!! Not the sides, the bottom/rear of the cage!!

Ask SheldonBrown!! It is to do with the lift not the width. There is no point in fitting a small chain ring that allows the chain to drag on the bottom of the cage.

__________________
Cheers,
George.

I prefer to read upright!

Anyway, I know what you were saying in your prevoius post and, IME, this is not wholly correct. So long as the chain will clear the bottom rear cross bar of the cage(clear enough?) on the 2 or 3 largest rear cogs, all is well. Those are your climbing gears. Why stay on the inner ring when the same gear is available on the middle ring?

The true limitations in the minimum usable size of the inner ring are 1)FD capacity, which can usually be slightly exceeded 2) the shape of the inner cage. Shimano will usually spec a min chainring size which, again can usually be slightly exceeded. In this case, we are exceeding FD capacity and recommended min chainring size by 2T.

Bottom line on using a 28T inner on an Ultegra Triple: it works. A 26T would be a bit dodgy on an STI road triple with a 52T outer and a 24T will probably be impossible.

__________________
Richard
Ozark Bicycle Service
http://www.ozarkbicycleservice.com

Obviously, you have just tried this?

Why dont you let sergen reply to the comments and not try to dominate his topic? You don't have to be right. Mr B was right in his opinion of you...

Sergen, if you would like to e-mail me I will forward to you a 5 page PDF from Shimano on frame design and fitting front derailleurs and chainring sizing. They you can decide for yourself.

__________________
Cheers,
George.

[QUOTE=gclark8]Obviously, you have just tried this?

Why dont you let sergen reply to the comments and not try to dominate his topic? You don't have to be right. Mr B was right in his opinion of you...

Sergen, if you would like to e-mail me I will forward to you a 5 page PDF from Shimano on frame design and fitting front derailleurs and chainring sizing. They you can decide for yourself.[/QUOTE]


Just tried what? A 26T inner with a 52T outer on an STI road triple? As a matter of fact, yes, I have, And yes, it can be done, but it can also be fussy to set up.
IME, a 28T is a much surer bet.

Here's the germane PDF, the one for Sergen's FD:

http://tinyurl.com/dnc6w

(and yes, I know this is for the braze on; the PDF for the band mount lists specs for the double. E.g., capacity is listed as 15T. The cages are the same.)

Let's look at two things listed under specifications:

1) Front chainwheel tooth difference (aka, "capacity"): 22T or less

2)Minimum difference between top and intermediate: 13T

Now, IME, it's possible to safely exceed the FD capacity by a little on an STI triple, but nearly 20% (i.e., 22T to 26T) is pushing it for reliable perfomance. If you really need to push the envelope, give it a whirl; if not, why bother?

Also, the minimum difference between the top and intermediate is actually a pretty tight spec. The cage will foul the middle ring if you vary by much. So, were Sergen to reduce the 52T top (outer) to, say, a 50T, he would also need to chenge the intermediate (middle) ring.

As a 28/27 seems to give him the gear he desires, why would one want to go through all the fuss to try a 26T inner? (Unless, of course, one has one to sell.)

One last thing, George, as this is a public forum, I will comment as I see fit. If that bothers you, you know where the off button is, right?

__________________
Richard
Ozark Bicycle Service
http://www.ozarkbicycleservice.com

NO!! Left!!

See you are not right all the time.

__________________
Cheers,
George.

George

Is that 26T ring suitable for 9 speed, and have you tried it out?

I have been considering trying a 26T granny instead of the 30T on my sirrus pro to make it easier to spin hills. current is 52/42/30

I don't know whether you would have to change the 42 to say 40 or 39 for the shifting to work well enough.

Mike