Angle of attack is a concept that will often come up when discussing the difference between different wheel sizes. To measure angle of attack, we place a square edged block in front of the wheel. The angle of attack is the angle of a line that is tangent to the wheel at the point of contact with this obstacle. In BikeCAD version 20.0 we have the option to display angle of attack for any size obstacle. The height of the obstacle is set in the Angle of attack tab of the Fixturing dialog box. For a given obstacle size, we can observe how the angle of attack will change if we move through a range of wheel sizes from a 20" BMX tire, to a 26" mountain tire, to a 27.5" mountain bike tire to a 27.5+ tire to a 29" tire. The larger the tire, the smaller the angle of attack and the more easily the bike will roll over the obstacle.