spencertimm

Hi all - I recently built up a Giant Revolt with the GRX Di2 groupset. I took it on its maiden voyage today and noticed that shifting from the small ring to the big ring with synchro mode turned on is pretty poor. The chain kind of binds/jams up before finally making it on to the chainring. Turning off synchro mode improves this quite a bit.

Could also have to do with the block that assembled it (me).

Taymob

Did you download the software update and calibrate it ?

spencertimm

Software has been updated. Can calibration be done with the app or do I need the PC software?

Iride01 

When you are shifting fully synchronized, then the back is shifting more or less at the same time to give you then next lowest or highest gear combo. I've never liked the way my Ultegra R8050 shifted out of the box in full synchro. My 105 5800 cable pulled group shifted much faster and efficiently when front and back shifts were done at the same time.

For me the one that interrupts my cadence the most is dropping to the smaller front ring. However changing it to shift to the small front sooner than the default setting and changing the rear to shift to the appropriate ratio at that time seems to have helped. Or at least it makes that chainring shift at a time when it's not necessary for it to be as perfect as my other bike did front and rear shifts simultaneously. IE. The shift to the smaller front ring happens soon after I start up a hard hill and not near the top where interruption to my cadence might be disastrous.

Increasing the shifting to take place very fast also seems to have helped, but I'm not absolutely certain on that. That reads more on how fast the shifting to each gear reacts to how long the button is held down. But I want fast shifts anyhow when I hold the button down.

I sort of suspect that part of the issue you are having is more that your cadence might be very low at the time when it's shifting and the front and back aren't getting a chance to complete the needed shifts.

Koyote

This is my experience, too. In Synchro, my Di2 doesn't quite shift the FD and RD simultaneously...Rather, FD seems to shift first, then RD shifts with a very slight lag. It's most noticeable when going from large to small chainring, as that is a quick shift -- and then the RD catches up to the cadence-matching cog. The result is that my pedaling cadence speeds up dramatically, then slows back down. Very annoying. This is why I use Di2 in the normal mode (don't know if it has a name) and shift both derailleurs myself. By hitting the right paddle first and holding it down for a second, then hitting the left paddle, I get the same result as a double shift on a mechanical groupset.

My shifting is set to the second-fastest setting. I'm not inclined to go to the absolute fastest setting, as Shimano warns that it might blow up if you're not pedaling fast enough when shifting.

grissley

I got exactly same experience - going from 46 to 30 takes ages. First, 16 teeth reduction apparently takes far more time than it took on my previous bike, where I had a cross 26-36-48 crankset. Then, on that previous bike (i had XT groupset) I was pushing both lever simultaneously to reduce 1 gear back in the same time - and the FD and RD were also moving simultaneously. In GRX, it seems that it is sequential both in full synchro and semi synchro modes. For this reason I am using manual now, but it is somehow totally crazy, as it neglects the sense of using something that was supposed to be one of the major pros of Di2 Moreover, I think in manual it is still sequential, not simultaneous. If I press simultaneously both buttons to change FD and RD, the lag is smaller than in semi-synchro, but I still can very well feel the 1st click (front gear changed) and then the second "click" (rear gear changed). Takes faaar more time than with my previous, classic XT, kills much of fan. I actually regret switching to Di2...
EDIT:
Switching manually is the solution, when following this approach:
1. Tap rear reduction
2. (a nanosecond later) tap front reduction
This works brilliantly. Unfortunately, only 1 gear rear reduction possible this way when going to 30 chainring for everything to shift smoothly. But smooth it definitely is.