There’s a lot of information on a tire’s sidewall if you know where to look. Of course you have your make and model, but if you look closer you’ll see an alphanumeric string on there — something like 195/75R15 — that tells you everything you need to know about your tire. You got your tire class on there, your aspect ratio and tire diameter, and all kinds of other useful stuff. All the way at the right, at the end of the string, there’s a two or three-digit number followed by a letter. The letter is your speed rating, but what we’re interested in is that number — the load index.
A tire’s load index, as the name suggests, indicates how much weight a tire can support when it’s properly inflated to the manufacturer’s specifications. It’s a two or three digit number (depending on application) that corresponds to a given weight on the load index chart. The higher the number, the more weight a tire can carry. When multiplied by four, your total should be larger than your vehicle’s gross vehicle weight.
For example, my 2022 Kia Soul GT-Line calls for 235/45R18s (I run Coopers, if you’re curious) with a load rating of 94. Looking at this chart, 94 is 1,477 pounds. Multiplied by four, that’s a total of 5,908 pounds. The Soul’s curb weight is 2,844 pounds, and its GVWR is 4,023 pounds. That’s well within the tires’ total weight index, so I’m good to go.
So, why does it matter?
In a word? Safety. If your tires can’t handle the weight of your vehicle and any passengers and cargo, they won’t keep you on the road very well. Think about it this way. How much weight can you carry? Now imagine you had to double or triple that amount of weight. What do you think would happen? Your legs would give out, right? Same with overloaded tires. At best, overloaded tires will wear more quickly and degrade performance. At worst, they’ll blow out and cause a crash. You should always buy tires that meet or exceed the manufacturer’s load index rating.
To make sure you’re getting the right tires with the correct load index, the manufacturer typically provides that information in two handy, easy-to-find places — on a tire data plaque on the driver’s door jamb and in the owner’s manual. If your car is missing both of these, there’s always the internet.
It’s also important to note that the load indexes and tire types discussed in this article are for passenger cars as designated by the letter P at the beginning of the tire sidewall data. Light truck or trailer tires, those with an LT or ST tire code prefix respectively, have two load indexes separated by a forward slash. For example, Toyo makes a light truck tire called the Open Country that can be had in LT235/75R15/6 104/101S. See how the load index is 104/101? Light truck tires are rated like this because they’re often used as a pair on a dually, like a Silverado 3500HD. The smaller number is used to factor your load index when used on a dually, and the higher number is for single use.
