We get asked sometimes…
Loads of room for a 2.25 with the sliders right up to the front, wouldn’t go any bigger or mud clearance might become an issue.
You won’t get tyre rub on the frame, even when really stomping. I can get the front mech to touch the (2.25″) tyre, just, in granny ring (and obviously riding SS you won’t have a front mech to care about!), but it won’t get near the frame unless you’ve got really REALLY flexy wheels!
Couple of pics attached to give an idea of clearance/how far forward the sliders are (sorry about the silly large size)