Hi,
Been away from the forum for quite a while. Back with a question. A friend of mine has Ultegra 105 shifter and R.D. Up front an FSA 53-42-30, he wants to go to a 11-34 cassette. Obviously, he will need a new R.D. with long cage, I suggested a RD-M771 SGS. I know that he is off a little bit in the spec. dept., having a 53 large chainring. Is this setup doable ??
Chain length, will a 116 links long enough or does he need longer chain, frame is medium.
Thanks.

That is a bit of a stretch but I bet it is doable. But why not do a much more reasonable choice, a 52/42/30 and a 12-32 cassette. 2 of my bikes have that combo and it works fine. There really isn't much point to the 53 or the 11 when the 52 and the 12 will cover about 95 percent of what you can attain with the 53 and 11.

First of all, he really should consider a 12-34. 53/11 is silly, especially if he's the kind of rider who needs a 30/34 gear. That said, the official capacity of the M771 SGS is 45T. With a 11-34 he'll exceed the chain takeup by one, and if he doesn't make a habit of cross chaining on the small chainring he'll be fine. With a 12-34 he'll even be in spec.

I don't know offhand if a standard chain is long enough.

My recumbent has a 52-42-24 up front and 11-34 cassette on the rear. It works fine with a standard Shimano "mountain" rear derailleur.

Another possibility is to switch the 30T granny for a 26t or 24T chainring. Cheaper than a new cassette and rear derailleur and a 24x27 is the same as a 30x34

Thanks guys for all the advises. Might go with a 12-34 to stay within the spec. I see that it is only available with Shimano XTR. Can't find any Sram with 12-34 range. One more question on XTR cass. Is it compatible with standard/regular Shimano hub ????. If I'm not mistaken, years ago, XTR and Dura-Ace had their own hub, I suspect that it has changed but not sure.

Early 10 speed dura ace freehubs had deeper/taller splines than standard shimano freehubs but they dropped that shortly afterwards. You can still use an early 10 speed cassette with the deep grooves on a standard shimano freehub, but not the other way around.

On our T50 tandem, we're running 54-44-26 with 11-34 9 speed, SRAM X.9 long cage RD, with no issues.

Tandems need wider range gears than singles; and 54/11 is used on flats with a tail wind or slight down grades.

To determine chain length, you need not only the sprocket teeth count, but also the dimension from the center of the BB to the center of the rear axle.

Its doable, but why?...

My touring bike is 44-34-20 and 11-36.....works just fine with sgs derailer.....I do not use index shifting.

I have 52-36-24 chainrings and a 11-34 cassette. A 116-link chain won't fit over the 52-tooth chainring and the 34-tooth cog but I only do that when I'm working on the chain or gears and shifting through all the gears to test adjustment or spread lubricant.

That used to be a quite common conversion. All that it takes is a mountain bike rear derailleur and a new longer chain to safely cover the 53/34 gear combination. Can't predict the actual number of chain links needed because it partially depends on the bike's chainstay length.

https://ridewithgps.com/routes/1055578

The initial climb starts 3 miles from the beginning and is 3½ miles of 10 to 15 percent. Hauling my 220 pound lardass up it without exploding my knees was one long granny gear grind. The descent down the other side was a lot of fun, though- accelerate past 45mph, then brake for a switchback. I ended up blowing the rear tube when the rim strip melted.