Chapter 40 follows the state of the rubber: unvulcanised in headings 4001 to 4006, vulcanised non-hard after that, and hard rubber at 4017. Vulcanisation is the fact that moves a good, not how it looks or how elastic it is.
Tyres are where the errors gather. Heading 4011 subdivides by vehicle type — motor car, bus, agricultural machine, aircraft — never by size or brand. A retreaded tyre falls in 4012, never 4011, and inner tubes have a heading of their own.
Every number opens on the lines beneath it, down to the ten-digit classification number.