Shimano 11/42 cassette, 11 speed derailleur compatibility

Question

Existing trek domane SL6 (2021) with ultegra 11speed mechanical gruppo

shifters r8020 fd r8000 with 2x 46/34 rd r8000 11spd 11/34

To get shorter gear inches, looking at changing to 11/42 ( or 11/46) cassette and uncertain as to best rd for it Based on forum discussions, considering 2 rd

A. XT m8000 sgs/long cage with wolftooth road link direct mount/11spd Vs.

B. Grx r810 long cage ( without wolftooth goatlink)

Any chain recommendations for either option

Which option would have better shifting and less strain on the drive train Thank you

Answer 1

What seems to be the least worst solution to me is a another option/hack: GRX-RD812 (the 1x version of the GRX, rated for 11-42 cassettes), with a XT-M8000 SGS cage - you just need to buy the inner and outer plates. I discussed it in this question, it hasn't been answered here, but you can find some instances of it online - there are some videos in the question linked. I haven't tested personally though, but am planning to when the cassette will wear out.

My experience with using rear derailleurs rated for 36T (I tested with an Acera and an Advent 11-42 cassette) is that shifting in the smallest sprockets is sluggish, and you frequently need to shift 2 gears in one way, then one back to shift one gear. It was below what I could accept from an Acera, so the perspective of having below Acera-level shifting performance from a upper-end groupset is not an option to me.

The tanpan/shiftmate seems to be an option as well, but I don't see any benefit over the RX812 with the M8000-SGS cage: you add another device, that is apparently very complicated to install correctly (it needs to be perfectly aligned to work properly, and not sure it will stay aligned when installed). And it is also more expensive than the 8000-SGS cage plates.

But as pointed out by Nathan, going for a 46/30 GRX crank may be an option as well (with the matching front derailleur), but won't get you as low as a 11-42 cassette.

Answer 2

Neither of those are options. Shimano 11 road shifters don't index with mountain 11. RD-RX810 won't clear a 42 and even if it was dropped with one of the Wolf Tooth things to do so, it still wouldn't have the total capacity needed.

To do this without changing the crank, using an adapter such as a Jtek Shiftmate with a mountain RD is one possibility.

However, this is the age of 46/30 cranks being an easy off the shelf solution that performs excellent without any adapting or hacks, so that's the first place I'd look. FC-RX600-11 plus FD-RX810.