I can't speak for the Roubaix but I've a Tiagra Synapse. I've really enjoyed it - I picked it because it was a deal on a last-season leftover.

I tried a 28 tire on the rear and it would rub so I went back to a 25. I've been thinking of some of the intermediate sized tires if I could fit a 26/27 in there but 25 works out fine for me so I've not pursued.

I'm around your weight as well and not had a tire issue**. I pump up the rear to about 100-110psi and the front is ~90psi. I believe the manual notes that the bike's rated for a rider up to 275lbs/125kg


**except when new: it seemed to never hold air (20-40psi loss per day). I told the shop when I took it in for a tuneup and they said it was fine. After blowing out the tube on a ride that I neglected to check: I replaced the tube and it's held air just fine since.