LastKraftWagen

Liking more and more the idea of running my DI2 and the two inner chainrings on my Shimano triple, especially since it appears my Burley came with some odd-ball BB configuration and it may be best not to mess with it.

So, herein I've read that the 48/30 config shifts well with the DI2 FD, any opinions on a 50/32 config? Otherwise I plan to go with the 48/32 [note all the above are large/small chainring]. I'm running a 11-36 cassette, and if I ever needed a 30/36 (f/r) gear it may be time to retire and move someplace flat.

Secondly, there was some discussion on spacers and grinding chain bolts, could anyone offer more detail on this? I couldn't see the photos, and somehow the descriptions were lost in translation. I'm running left-side timing, and while playing with an extra crankarm it looks like I would only need a washer where the outer chainring would normally mount to take up the "slack" in the chainbolts. Unless my install is easier than the ones described, or I'm doing something bass-ackwards, I can't see the need to grind the mounting bolts. Is it because I'll be mounting an outer ring in the middle position? The difference may be so slight (but significant) that I can't feel it.

Sorry for the dumb questions, in a state of perpetual learning and WAY behind the curve.
Thanks

chojn1

LKW,

On a triple crank set, the middle chainring have small indents on the inside face for the chainring bolt/nut flange. Those indents are on the outer surface of the outer/big ring. When you move the big ring to the middle position, you lose those indents as they now face the spider. The flanges of the fixing bolts for that ring will thus protrude out more toward the small ring. With certain gear combination (small chain ring and small cog) the chain will rub against these flanges.

I solved that problem by adding 1mm washers between the inner granny chain ring and the spider moving it more medial and away from the big chainring.

The 48/30 crankset with a 11-32 cassette shift flawlessly for me. I cannot imagine that a 50/32 would cause any problem. The 11-36 cassette, on the other hand, may require some modification to the DI2 rear deraillleur.

If you already have a 30t granny it may be easier to switch out your cassette than to buy a 32t granny and still have to modify your rear derailleur.

Have fun experimenting.

CJ

twocicle

Since you are not doing the same-side drive thing, the change to a 2-chainring front is really simple. Likely you will be able to reuse the same chainring bolts/nuts that you already have, as long as you put something in place of the outer chainring.

Here are a couple ways to finish off your outer ring mount:

#1 :



or #2 , use Race Face crank arm tab spacers as shown here:



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As mentioned by CJ, depending on your big ring's chainring nut head thickness, you will likely need to add ~1mm spacer to your granny.

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As far as using a cassette > 34t, you will need to get the expensive K-Edge RD cage installed. I managed to squeek out a 34t using a mid length cage from a RD 6700A (GS) + a 10 tooth upper jockey wheel, but no way to go up to a 36t cog without a seriously long cage on the Di2 RD.

LastKraftWagen

Thank you both, makes much more sense.

Already running the K-Edge and the 36T cassette, as soon as my first DI2 grupset came in I sent off the RD to be modified. I now have two modified RDs, always carry the spare on multi-day rides or whenever I expect to be outside 40 miles from the house...Not ttoo heavy to throw in the CamelBak and you just never know...But you can bet the house that no LBS will have the necessary replacement.

May just go with the 48/30 as I already have a 30T granny and the 50/32 only loses about a 1.25T at the low end and gains 0.44T at the high end and I don't think I really care that much. Gonna sleep on it and order in the morning.

Thanks.

twocicle

Which model of Shimano triple do you have on the Burley?

Chris_W

If you have the Shimano Ultegra R603 cranks then you're going to have a big problem because there are no regular inner ring mounting posts. You can change the middle ring to a TA Specialites Tripleizer to get a standard 74mm BCD for the inner ring, but I don't think that the Tripleizers come in anything bigger than 42 teeth.

LastKraftWagen

FC-1057 (TC-1057?)

Always thought they were Ultegra, until I actually found someone to pull out the magnifying glass. These are actually 105SC level circa 1990s.

Went ahead with the 50/32 rings...We'll see how it works.

twocicle

FC-1057 = Shimano 105 (5700 series), 8 speed. The default spacing between granny and middle ring with that crankset should provide plenty of clearance, maybe a bit more than the Di2 FD will handle. In that case, just add some spacers to the "big ring" (middle ring mount position) to move it closer to the granny if needed.

LastKraftWagen

Yeah, when I found the specs on the 1057s I figured that may be the cause of my current shift problems using the two outer positions (with no way of shimming either ring closer to the other). Should be easily fixable using the two inner rings.

Chris_W

Just to be picky, I think you meant it was the equivalent to what you could call the 5400 series, although I don't think Shimano ever called it that, but it came before 5500. 5700 is the current generation (until next month when 5800 will start to be released).

Dean V

If you can get along fairly quick you may find the 50t a bit small. Not so much because the 50-11 isn't enough gear but because you will quite often be down the small end of the cassette and the 11-13-15 are quite big jumps. I find them ok for downhill runs but a bit much for hammering on the flat. 15-17-19 I can more or less tolerate.