I would guess a 28c randonneur is quite laterally stiff?
my argument stands.
Compared to a 23c no way. Because a 28c has a greater surface area and despite being a good tyre doesn't (can't physically) have the same stiffness laterally as a 23c because it's simply bigger and has more material to flex. As long as it's a modern 23c tyre that has some form of puncture protection (these are the ones that are naturally more laterally stiff due to their armour).
Compared to a 23c no way. Because a 28c has a greater surface area and despite being a good tyre doesn't (can't physically) have the same stiffness laterally as a 23c because it's simply bigger and has more material to flex. As long as it's a modern 23c tyre that has some form of puncture protection (these are the ones that are naturally more laterally stiff due to their armour).