These two topics are fairly straight forward, so I’ll cover them in one article.

Come to think of it, why people have such a hard time explaining what the section width and aspect ratio are continues to elude me.  People in the tire business for years and years know what it is, can articulate what it is, but can’t translate it from tire lingo to “normal speak”.  I see customers leave my shop every day with bewildered looks on their faces because one of my tech just put them through the information wringer.  So I’ll attempt to break it down in basic term that everyone can understand.

Section width is the width of the tire.   There, simple right?  I’m sure most people reading this are asking “what width?” right now, and that’s where people usually get hung up.  So if we’re looking down at a tire that is stand up in a position where it would roll away if you pushed it, such that we’re staring down at the tread, the section width is basically the width of the tread in millimeters.  It goes a little further than that but measuring from the fattest part of the sidewall on one side to the fattest part on the other side, but that’s not so important.

So a LT275/50R16 91S is 275 millimeters wide from sidewall to sidewall if you were to puncture the cheap tire at its widest point with a ruler.

Now, sidewall aspect ratio is not an absolute measurement like section width is.  It is a percentage of the section width, and determines how “big” your tires are from the rim to the tread.  This is also referred to as the tire section height, aspect ratio, or profile.  For an example, our LT275/50R16 91S measures 137.5 millimeters from the tread to the rim, because 275mm x 50% = 137.5mm.

That means the higher the aspect ration the taller your tire will stand.  At the same time, the greater the tire section, the greater your tire will stand.  So both of those figures play into the actual size of your tire.  Remember that, it’s important.