>>1579160if the cranks are 160 mm the bike is 14.5 inch
if the cranks are 175 mm the bike is 15.7 inch
the 1 inch or 1 1/8th inch quill is used for smaller measurements
another way to check is assuming the max chainring size .eg 48 x 12.7 = 609.6 / 3.141 = 194.078 mm
x2 = 388.156 + 25.4 = 413.556 = 16.28173228 inches
26 inch mtb of the time period tend towards 19 inches because of the way the top tube slopes