A couple of things to add to the recent discussion:
- In general wider is better but there is a point past which the added weight of a wider tire becomes noticeable. I think the sweet spot is 28-30mm for road slicks, but that's just my opinion. So I'm still a believer of "widest tire your frame can accommodate" but for me that's 27mm true width 😅 On my townie or gravel bike I do notice a big difference going from 28mm which still feels like a road tire to a 32mm or bigger which firmly puts me in commuter mode.
- It is perfectly safe to have a bulb profile. You lose some aerodynamics but people have been riding 2.2" MTB tires on 15mm IW rims since the 90s and not very long ago folks used to race CX on narrow 19mm OW rims with 33mm tires.
- I can imagine a lighter rider getting away with riding 23mm tires still, but for folks above a certain weight I think 25mm would be the minimally acceptable size.
- A while back I rode 22mm Conti racing tubulars pumped up to 130psi. Compared to GP4Ks at 25mm (27mm true width) at 95psi, I guess the GP4Ks were more comfortable but the skinny tubulars were objectively faster (mostly excellent tarmac with short sections of poor tarmac) and not uncomfortable despite being pumped to 130psi.