Cheap Tire

Cheap Tire Guide


Tire Section Width and Sidewall Aspect Ratio

Published October 24th, 2008 in General Tire Information, Tire Sizing | No Comments »

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.

Interpreting Cheap Tire Size

Published October 24th, 2008 in General Tire Information, Tire Sizing | No Comments »

There’s a code on the side of every single tire that you’ll run across.  Or, more accurately, there should be a code!  If there’s not your best bet is to move on and find a different source.  Any set of wheels without the required manufacturers’ information likely has more problems than just that.

Let’s make this simple and move left to right, interpreting what the characters mean as we go.

P225/50R16 91S

Most tires you will run across will start with the letter P.  This signifies that it is of the “P-Metric” size and is engineered to fit on most passenger vehicles.  This includes but is not limited to minivans, cars, light duty trucks, and SUVs.  A cheap truck tire will have the same markings as an expensive one.  A cheap minivan tire will as well.  Think of the P as standing for passenger.  All it is really, though, is a standard for sizing the wheel.

If it does not begin with a P (like this 225/50R16 91S), it still means it’s a passenger vehicle tire, but it is sized by the metric system.  Most European cars will have tires of this type.  The two sizing conventions are typically very similar.

The size can also begin with an LT, which means the tire was designed for use with a light truck.  But don’t be fooled by the use of the term “light truck tire”, it’s using the term in relation to tractor-trailers and heavy-duty commercial trucks.  So LT means 3/4 and 1 ton pickups that are capable of carrying 3 to 4 tons of payload.

ST tires (ST225/75R15) are “Special Trailer” use tires that are generally an odd size designed for use with a specific cargo trailer, and should never be used on a passenger vehicle.  If you’re looking for a cheap trailer tire, it will likely have ST as the leading characters.

Of course, T stands for “temporary service” and will likely be included on your spare tire, unless you have a full size that you bought with a set.