There are letters on the tire’s sidewall that correspond with “tire load range,” historically known as the “tire ply rating.” Load range and ply rating specifically refer to how much load your tire can support at maximum allowable air pressure.
Which came first, the tire or the air?
Before getting down into the nitty-gritty of what tire load range is and what it means for you and your vehicle, it’s important to understand it’s not so much the tire that carries the weight — of your vehicle, of your body, of your belongings — as it is the air inside your tire.
That said, if you’re going to be hauling a super-heavy load — maybe a load that’s over the maximum load recommendation for your particular set of tires, per industry standards — then you’re going to need more air to support that load of which your current tires cannot support. Therefore, bigger tires with a higher ply rating can hold more air and, thus, can carry more substantial loads.
Tire load range vs. tire ply rating
You may hear the terms tire load ranges and tire ply ratings tossed around together — one, which is designated by letters, and one, which is designated by numbers. They are actually terms from radically different historical eras that mean basically the same thing. Load ranges and ply ratings are both used to identify load and inflation limits for any given tire.
The historical term ply rating goes back to the days when bias ply tires were actually constructed of layer upon layer of cotton fabric — yes, cotton. Ply rating referred to how many layers, or plies, of cotton had been used in the tire’s construction, and the number of plies determined the strength of the tire.
In today’s modern world, tire plies are no longer made out of cotton. Now, tires are constructed using fewer, yet much stronger, plies so the term ply rating doesn’t refer to the actual number of plies anymore. Instead, the ply rating indicates an equivalent strength compared to early cotton-constructed bias ply tires.
If you see ply rating and load range on a chart, they both represent the tire’s maximum load carrying capacity at maximum allowable air pressure.
Load ranges per vehicle
Whether you drive a regular passenger vehicle, a light truck or even a heavy truck, each will be riding on tires that have been specifically constructed to hold the weight of your vehicle. Each set of tires is branded with their unique load range. The information needed to identify the load range for tires is right there on the sidewall.
Passenger tires are typically manufactured in one of three load ranges — standard load, light load, and extra load or reinforced — all of which could range from 2 to 4-ply tires. As evidenced by its name, the standard load range is the most common. If you take a look at the markings on your tires, you will be able to tell that your set is in the standard load range if they have either no letters or an “SL” on their sidewalls (sequence of letters and numbers). Your set of tires is in the light load range if they are branded with an “LL” in their sidewall descriptions. And finally, your tires are in the extra load or reinforced range if they include either an “XL” or an “RF” in their descriptions.
If you drive a light truck, you’re likely riding on tires that are marked with an “LT.” Again, take a look at your tires, and find the sidewall descriptions in order to tell the load range. Light truck tires typically have load ranges of B, C, D, E or F — all of which have different, corresponding ply ratings — 4-ply rated, 6-ply rated, 8-ply rated, 10-ply rated or 12-ply rated, respectively.
Last, if you’re pulling a trailer that requires special trailer service tires, those tires are going to be labeled “ST.” You’ll be able to tell the specific load range on the tires’ sidewall descriptions. Special trailer service tires have load ranges of B, C, D or E, which correspond to their specific ply ratings — 4-ply rated, 6-ply rated, 8-ply rated or 10-ply rated.
Still not sure how to find your tire load range? See a tire professional who would be more than happy to help.