Originally Posted by
akexpress
I don't think this is how it works It will shift both derailleurs at the same time as needed to sequentially shift. As DI2 shifts are almost instantaneous already this should be a really slick smooth system.
Right. The system will automatically shift the front and rear to smooth things out.
I was just saying that if you still wanted to pre-set the front chainring you could accomplish the same thing by over-shifting then coming back.
So for example:
shift +1: +1 RD
shift +2: +1 FD, -1 RD
shift -1: -1 RD
Shift -2: -2 RD
You've effectively shifted the front without changing your ratios. Now when you start upshifting, as you accelerate you would have a bunch of gears before another front shift.
The trick behind the sequential shifting is that the cross-over points are different going up or down, so that you're never stuck constantly shifting the FD as you go up and down a gear or two.