100/90 is called the aspect ratio..
The face (tread) width of the tires is 100mm.
The sidewall of the tire is 90% of the tread width... or.. 90mm as Nate has said..
The width of the rim (inner space between the beads) plays a role in this as well..


Build it the way you want it ..... then learn how to ride it like you own it..
www.lowridersbysummers.com


Last Edited By: lowridertommy 03/11/14 1:43 PM. Edited 1 times.