I thought I read that the 2018 Synapse takes 32mm tires. Is that the model you linked?
Anyway, couple items: 1. I have a somewhat hard time imagining 4mm making a difference preventing a tire from getting into a crack. 2. If it comes with 28s, there’s gotta be at least 4-5mm clearance. And that means Conti GP4ks2, their 28s mount up 30mm, and they’re awesome.