Trail Calculator (Bicycle Geometry)

Here lies a Tableau viz to calculate trail (both geometric and mechanical) and wheel flop. Pneumatic trail is calculated using the classic formula:

([Wheel Radius] * COS([HTA] – [Rake]) / SIN([HTA])

Bolt Circle Diameter

My take? The best BCD is 50.4/80BCD like the vintage TA Cyclotourist, and Stronglight 49D. Those are jim dandy, but opt for one with a standard JIS extractor like the offerings from Velo Orange, SunXCD or vintage Sugino (PX and Super Maxy) and others. I welcome more narrow-wide chainring offerings (at the time of writing, the only know such ring is a TA 38T, available from Cyclodonia in France or I’s in Japan).

Why 50.4/80BCD? This pair allows a wide range of tooth counts, including some very small and large rings, but at prices less dear than the (very, very nice) Rene Herse 3-bolt and the White Industries VBC cranks. And I think they’re beautiful.

Tire Size and Air Volume

Air volume was calculated in MS Excel with the following formula (this example is for 650B/584ISO with 38mm tires):


This will give results in cubic millimeters. Volumes above have been convert to liters (dividing by 1 million), rounded to the nearest tenth.

Some variances may be introduced from rounding, unit conversions, and other factors.

This is all white coat, clean room, armchair nerdery stuff only. Real life measurements of tires can vary based on many factors including miles, rims, tubes, production batch, etc.

Tire weights are manufacturer published weights, except for Schwalbe which were 100% fabricated for my own amusement.