DD,
They are Vittoria Rallys, 25s, You might get 28s in, but the rear chain stay bridge would be the limiter. The seat stay bridge and front fork crown have plenty of clearance for larger tires (height and width.)

Thanks, that was last year's picture, it has green Newbaums tape now, grey Campag cable housings, and fresh Rallys mounted. I'm very grateful to you for everything SC.

Bill