So, my Felt FR Advanced nominally takes up to 28 mm, but I think there is sufficient room for 30s, even with my super-wide hookless rims.
Going up to 30s in the rear would help greatly help with comfort and punctures, since its hard to keep my rear tire off the rim at the maximum pressure of 72.5 psi because I am quite heavy.
Yea or nay?
How much clearance is there with 28’s? You can check by passing an Allen key around the tire where it clears the seatstay chain stay and fork. See what the biggest one that passes through is.
Also consider if you ride dirty or wet roads that can cause grit to cling to the tires and rub on the frame. Maybe apply protection tape if you end up pushing the clearance pretty close. I would say anything less than 4mm is a bit sketch.
And even the stiffest wheel has some side-to-side flex. Good clearance in your garage may not translate to good clearance on the road. How much you need will also depend on how aggressively you ride, and in what conditions. A pebble trapped between tire and frame can leave a nasty scar on the frame.
It’s about 4 mm. Maybe I’ll just get some inserts…