How to read a tractor tire size
480/70R38, 16.9-30 8PR, 14.9R28… what the markings on a tractor tire mean.
Radial metric sizes: 480/70R38
- 480 – section width in mm.
- 70 – aspect ratio (sidewall height as % of width).
- R – radial construction.
- 38 – rim diameter in inches.
A code such as 141A8 follows: 141 is the load index, A8 the speed symbol (40 km/h).
Bias-ply sizes: 16.9-30 8PR
- 16.9 – width in inches.
- - – bias (cross-ply) construction.
- 30 – rim diameter in inches.
- 8PR – ply rating; higher means more load capacity and pressure.
Mixed: 14.9R28 and 380/85R28
14.9R28 is a radial with an inch width; on the same rim it has almost the same outside diameter as 380/85R28. See the radial ↔ bias-ply equivalents table.
If unsure, take a photo of the sidewall of your current tire.