Maxxis M6016R-90/90 R12 54J

90

90 is the width in millimetres of the tyres cross section.

90

90 is the Aspect Ratio, it is the ratio of the sidewall height to the cross section width.

R

Radial construction.R stands for radial-ply construction.

12

12 inches, stands for the diameter of the wheel that the tyre is designed to fit.

54

54 is the load index i.e. the maximum weight each tyre can carry at full speed.

J

J is the speed rating i.e. the maximum speed for the tyre at full load.