I have a mostly-105 road bike (triple) with 105-5603 shifters/FD/crankset and an ultegra-6600 RD.

I got Ultegra 6603 shifters for christmas, and was going to install them and move the 105's to my commuting bike (which I'm installing a touring triple on). I was just about to make the switch on the road bike, when I stumbled upon this on the shimano website:

https://bike.shimano.com/publish/cont...ty%20Chart.pdf

Why does it list the 105-5600 separately from ultegra/DA for front shifting compatibility? I thought all front shimano road shifters used the same pull ratio, that separation I haven't ever heard of. Is this just a marketing thing, or is there some credence to this?

The problem may be with the xx03 part of the model number. With Shimano 10-speed shifters the Ultegra and Dura-Ace shifters are double or triple specific, the xx03 numbers are triple specific (but can work with a double). xx00 Ultegra and Dura-Ace shifters are double specific. It's my understanding that the 5600 105 shifters are double/triple compatible and can work with any 10-speed Shimano drivetrain. But the Ultegra or Dura-Ace double shifters won't work with any triple crankset.
No problem with throw ratios between these.
The Shimano compatibility chart is conservative, there are some combinations that aren't shown to work but do anyway.

Al

Yeah, I specifically bought a 6603 shifter set though. It only lists that as being compatible with 6603/7803 front derailleurs, and the 5600 shifters only with 5603 FD's, which I find confusing. In fact, had I not seen that chart, I would've happily gone on and done it. Maybe I should just forget I saw the chart.

Another possible issue- The derailleurs are probably optimized for the chainrings of their specific groups. The 105 10-speed triple has 50-39-30 chainrings. The Ultegra 10-speed triple has 52-39-30 chainrings. I think the D-A triples are now 52-39-30 chainrings but have been 53-39-30 in the past. I think what you have will work fine, there have been problems with running triple 10-speed front derailleurs on 9-speed triples, but that's not your concern since you have a 10-speed cramkset.

install them, the**03 portion of the id # tells you its for a triple and has an extra detent on the left side to trim the large ring. so you get small ring, position 1 on middle, position 2 on middle, poition 1 on large, and position 2 on large. why they didnt do this on 105 is a mystery to me. however I do know that 105 will work with a double or triple. In short if you have a 10 speed, and a triple crank, 6603 is what you need.