Tire Size -- What do the Numbers Mean?

[kelsorat]

I am curious as to what each number on a tire stands for. I've also noticed a possible difference in dimensions-possible between a tire with given measurement in metric as opposed to standard unit.
Can someone give me the explanation?

 

[CaptainObvious]

The current standard is as follows:

The first number given in the tire width in milimeters (100 = 3 15/16" also called a 4.00)
The second number is the aspect ratio; i.e. the height of the tire in relation to its width (a 100/100 tire is as high as it is wide).
The final number is the rim size in inches

so...

a 100/100x19 is 4.00x4.00x19

 

[kelsorat]

Thanks