I've ride with a 19t about half the time, and half of that time is two-up.
Runs fine, no issues. I live in Orlando, so there's no real grade (elev.) changes.
I'm 210 lbs, 380 lbs (+/-) when two up.
My bike is pretty light though, and I seldom have luggage. So total weight, fully loaded, is always under 900 lbs.
FWIW, the OTHER half of the time it has a 16t.
Changing from 16 to 19 ONLY involves changing the gear (duh), and re-adjusting the axle position, nothing else.
