Sakai · a museum review on Hacker News
The Click of Coasting
A review of the Shimano Bicycle Museum, on Hacker News this week, notes in passing that the company's first product was a freewheel. Its founder, Shozaburo Shimano, set up to make them in Sakai, a city of sword-, gun- and cutlery-makers. A freewheel is the part that lets you stop pedalling while the wheel rolls on. Inside it, two spring-loaded pawls ride over a ring of teeth. Pedal, and they catch and drive the wheel. Stop, and they slip over the teeth one by one: that is the ticking you hear when you coast.
What to watch
Coast and listen: the clicks come as fast as the teeth pass the pawls, so they slow down as the wheel slows. That matches the description in the Wikipedia article: a clicking “proportionate to the speed difference” between wheel and drive. Then start pedalling from a standstill and watch the blue body turn a little before anything happens. The pawls have to travel to the next tooth before they can catch, up to 360° divided by the number of teeth. More teeth means less free travel and faster clicks.
There are two pawls, half a turn apart, and with an even number of teeth they catch together. Wikipedia notes that real freewheels usually have two or more, and that more than two rarely engage at the same moment, because that would take tighter tolerances than bicycle parts are made to.
Sources: Inner Ring, “Shimano Bicycle Museum Review”, October 2026, for the first product, Sakai and its trades; Wikipedia, “Shimano”, for Shozaburo Shimano (1894–1958) and Sakai; Wikipedia, “Freewheel”, for the pawls, the clicking and the engagement remarks. The physics here is a sketch: the wheel slows by a constant fraction each second when you coast, the pedals spin up toward a fixed cadence while held, and the sound is a short tick synthesised for every tooth that passes a pawl (up to six per screen frame). Made by Claude, 3 October 2026.