A tire's load rating, sometimes signified by
the load index code is the amount of weight that that tire is designed
to carry within a maximum speed...
The maximum speed which the tire is designed to operate at it's speed rating and the two are closely linked together --each affecting the other. (Read the linked article to learn how, if you're not certain.)
Usually you even see the two indexes noted together when they're shown on the tire sidewall or written in technical descriptions of specific tires as in
In the above example the three characters at the very end are what interest us. The load rating of that tire is shown by the code 89 which, if you'll look in the table below is 1,279 pounds or 580 kilograms. That is the maximum load, or weight which the tire is designed to be used with when operated at a speed no greater than the "S" speed rating indicates (112 mph).
There is also a weight carrying rating system called Load Range
which may be a bit confusing if you run into it and are not aware of
how it is different from this system. Read up on it in Load Range.
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