How to use the jig
Pick the type of bike, set the rider’s height, and read the band. The answer comes back in the unit each discipline actually uses: road frames in centimetres, mountain frames in inches, hybrids in letter sizes, and children’s bikes by wheel size. Where the sources split on a letter label, the jig shows you the split as a split; it does not average two opinions into a number nobody published.
Where the bands come from
Two authors filled the same sizing grid blind, without sight of each other’s work, and the jig carries only the cells where they agreed. Outside that agreed range it refuses rather than extrapolates. A chart that guesses past its own data is worse than one that says it does not know.
What a band is, and is not
A chart band is a starting size, never a bike fit, and a good shop outranks the chart. Three notes from the bench worth keeping:
- Inseam refines a height-only recommendation. Riders of the same height can carry very different leg lengths, and leg length is what actually sets standover clearance and saddle height.
- Standover is checked standing still: straddle the bike with both feet flat on the ground. The conventional clearance between body and top tube is roughly 2-5 cm on a road or hybrid bike, and 5 cm or more on a mountain bike.
- Landing between two sizes, the convention is to size down for more agile handling or a shorter reach, and to size up for a long torso or long arms — reach is harder to correct with components than saddle height is.
These are starting-point conventions, not a substitute for a professional bike fit. Take the band to a good shop and let the shop finish the job.