1 LT: Designates that this is a Light Truck tire. 2  Load index and speed rating are sometimes not mandatory for flotation sizes, but must be for any tire approved for street and highway use. 3  2- or 3-digit number: Load index; see table below.  1- or 2-digit/letter combination: Speed rating; see table below.
https://en.wikipedia.org/wiki/Tire_code
Automobile tires are described by an alphanumeric tire code (in American English and Canadian English) or tyre code (in British English, Australian English and others), which is generally molded into the sidewall of the tire.
https://en.wikipedia.org/wiki/Tire_code
The load index refers to the load-carrying capacity of a tire, or how much weight a tire can support. For example, if a tire has a load index of 89, it can support 1,279 pounds (from below chart) at maximum air pressure. Multiply that by four (4 x 1,279 = 5,116 pounds) to get your maximum load-carrying capacity. It is not recommended to install tires with a lower load index than what came on your car from the factory.
http://www.flashoffroad.com/features/Tires/loadrating.html
Load Range / Ply Rating Identification. The load range/ply rating branded on a tire's sidewall identifies how much load the tire is designed to carry at its industry specified pressure.
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55
Differences in load capacities and maximum pressure are identified by their load index and the maximum load/pressure for single/dual applications branded on their sidewall. The example provided above is for single/dual applications of a 225/75R16C size tire.
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55
The TRA Inflation Tables must always be consulted when comparing the load capacity of P-Metric tires; the Load Index alone is not sufficient. An example: a P205/50R15 Standard Load tire has a load index of 84 and a load rating of 505 kg (1,113 lb) at 35 psi (240 kPa). A P215/50R13 with the same load index of 84 only has a load rating of 495 kg (1,091 lb), also at 35 psi (240 kPa).
https://en.wikipedia.org/wiki/Tire_code
What is Load Index? Load Index indicates the maximum load in pounds that the tire can support when properly inflated. You'll also find the maximum load elsewhere, in both pounds and kilograms. To convert this information to a Load Index, use our Load Index Table. When buying new tires, it is important to select a Load Index that matches or above the Load Index of the tires that originally came with your car. View Load Index Chart:
http://www.justtires.com/content/content.jsp?pageName=LoadIndexLayer
Since most P-metric passenger tires are manufactured in the standard load range, they will have nothing branded on their sidewalls or may be branded standard load and identified by an SL in their descriptions, as in P235/75R-15 SL.
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55
For Load Range B tires, ETRTO (ISO-Metric) standards specify the load index rating at an inflation pressure of 36 psi (250 kPa) (table below), while P-Metric standards measure the load capacity at an inflation pressure of 35 psi (240 kPa).
https://en.wikipedia.org/wiki/Tire_code
Today's load range/ply ratings do not count the actual number of body ply layers used to make up the tire's internal structure, but indicate an equivalent strength compared to early bias ply tires.
https://www.tirerack.com/tires/tiretech/techpage.jsp?techid=55
what is tire load index
Tire load index is the maximum weight a tire can safely support once it's properly inflated. A tire load index is the maximum load in pounds that the tire can support when properly inflated. Tire load index is the maximum load in pounds that the tire can support when properly inflated.