Top Tube Lengths

Generally, but not always, these are the ranges of lengths that top-tubes fall within commonly named sizes that you will find the major brands using. Nearly always expressed in inches, they are as follows and are beased upon LUXBMX's most popular sold complete BMX race bikes.
Micro (18 inch wheel) - 16.25” top-tube
Mini (20 inch wheel) - 17.25” top-tube
Junior - 18.25 to 18.75” top-tube
Expert - 19.5 to 19.75” top-tube
Expert XL - 20” top-tube
Pro - 20.5” top-tube
Pro XL - 20.7 to 21” top-tube
Pro XXL - 21.5 to 21.75" top-tube
Pro XXXL - 22” top-tube
Cruiser - 21.5 to 21.75” top-tube
Those lengths might not look like much of a variation from size to size, but remember, all or the parts that come with those sized bikes are scaled appropriately. Let’s break this down in the next section b looking at a couple of examples.