Tyre Width or Section Width : (Example : 255)
Tyre width in millimetres is measured from the widest point of a tyre’s outer sidewall to the widest point of its inner sidewall.
Aspect Ratio : (Example : 55)
Aspect ratio is the relationship between a tyre’s sidewall height and the tyre's width. The lower the ratio, the smaller the sidewall height, which means better cornering but a rougher ride.
Construction : (Example : R)
This indicates the tyre’s internal construction. They can be R (Radial) like most tyres, or D (Diagonal construction) or B (Belted).
Wheel Diameter : (Example : 17)
The number is in inches and indicates the diameter of the wheel on which the tyre is designed to fit.
Load Index : (Example : 72)
This indicates how much weight the tyre is certified to carry at maximum safe inflation. The numbers refer to a chart that specify the load capacity that the tyre can carry.
For example, 72 = 355 kg.
You can find yours in the load Index chart :