Joined: Jan 2009
Posts: 44,231
Likes: 6,489
From: New York, NY, and High Falls, NY, USA
Bikes: 1962 Rudge Sports, 1971 Raleigh Super Course, 1971 Raleigh Pro Track, 1974 Raleigh International, 1975 Viscount Fixie, 1982 McLean, 1996 Lemond (Ti), 2002 Burley Zydeco tandem
It used to be that the width rating was derived by flattening the tire out, measuring the distance between the two beads, and dividing by 2.5. I don't know if they still do that. This explains why there is a difference between rating and actual width: width to height ratio varies with the design and materials used.