My Bianchi 650B conversion has spent long periods of time with close to zero clearance at the chainstays. The Col de la Vie tires I started with measured about 36.5mm wide, giving about 1-2mm of clearance per side. Then, I switched to Pacenti Pari-Motos, which started at a full 38mm and grew to 40mm! After dimpling my chainstays I'm back to about 2mm clearance per side. With my true wheels and spoke wrench in the bag, I'm completely comfortable with that much.
