Shimano GRX chainset compatibility question

Equipment
1

Hi all. Happy New Year.

Probably a stupid question, but can you use a standard Shimano road chainset (e.g. 52/36 Ultegra) with the rest of the gearing being Shimano GRX di2? If I wanted to go for 52/36 up front and an 11-40 cassette at the back, would I need to swap in a standard di2 front derailleur (so ultegra di2 up front and grx di2 at the back)?
The GRX di2 front derailleur is apparently set 2.5mm further out than a standard Shimano derailleur, so I’m not sure if it’s compatible with an Ultegra chainset.

2

GRX chainset (crankset for US people) and the matching GRX front derailleur are 2.5mm more outboard (for tire clearance). So, it’s best to use matching chainset & FD (Road or GRX) to keep that aligned.

Besides that, I think mixing Road front and GRX rear can work. Just be sure to confirm chain takeup specs between the rear derailleur and the gaps between the chainset chainrings.

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3

Thanks Chad, that makes sense.

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4

Here’s a compatibility chart that MAY help. Di2 Compatibility - mix Ultegra, DURA-ACE, XTR, XT and GRX components

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Im not sure there rear derailer can take up enough slack for that wide of gear range,

6

I run an 8000 series Ultegra 46/36 up front and GRX 800 in back with 11-34 out back. I have no issues with the 2.5mm offset. I want to try a little larger cassette, but not sure if my RD will handle it.