If it's metric, does it have a 'P'? Does it have an 'LT'? When calculating, you should be looking at your vehicles placard in the door and finding the exact size. High Flotation LT tires are your standard 'American' light truck tire sizes with inch measurements and the 'LT' usually at the end (35X12.50R20LT). Metric LT tires will look like metric sizes but will have an LT in the front of the size (LT285/70R17). LT tires also come in two types, LT-Metric and LT High Flotation. However, they do have different load rating charts and should be assessed as different tires when calculating a new tire pressure. They are very similar and typically interchangeable. This actually designates a different size than the same tire size without the 'P' designation. You've probably seen a 'P' in front of some of the tire sizes you've looked at. With metric passenger tires there are actually two types, Metric and P-Metric.
When calculating a new tire's pressure to match an OEM tire's load capacity it's important to be very accurate.
The higher rated tire will then have added load capacity up to its maximum pressure rating. Similar to Passenger load ratings, multiple Load Ratings will carry the same weight at the same pressure up to the lower ratings max pressure. (B) 4-ply, (C) 6-ply, (D) 8-ply, (E) 10-ply, (F) 10-ply and so on.Īn LT tire size can have multiple Load Rating variants. Light Truck (LT) tires are rated using a tread ply system. Pressures above 35-36 psi for SL tires and 41-42 psi for XL tires will not increase the load capacity of the tire.Įven if you put 50 psi in an SL tire the load capacity will remain what it is at 36 psi for the higher pressure levels.Īdding tire pressure above maximum load capacity is used mostly for high speed situations.Ī tires air pressure is increased to reduce tire deflection for the increase in rotations per second compared to typically city/highway use. This added pressure does nothing for load capacity. Some tires list 44 psi and many higher speed tires will list 50-51 psi. The maximum allowed pressure listed on a tire's sidewall can be higher however. Light and Standard Load tires have a maximum capacity pressure rating of 35-36 psi and Extra load tires have a maximum capacity pressure rating of 41-42 psi. However, they have added load capacity above certain pressures.
Passenger tires will be rated Light Load (LL), Standard Load (SL), or Extra Load (XL).Įxtra Load tires of the same size will typically have the same load capacity at the same pressure as the Standard Load tire. Too little air can wear the tires unevenly on the outer edges and will reduce the tires load capacity below the engineered level.Įach tire is rated with a load range, load index number, and max pressure rating. Too much air can wear the tires unevenly in the center and can create a wondering effect on the vehicle's handling. Tire load capacity is directly related to air pressure in the tires.Īs tire pressure goes up or down, so does the load capacity of the tire. The size and pressure have been engineered specifically by the manufacturer for correct load capacity and will typically render the best results for tire wear and ride quality. Listed inside the driver's side door jamb of your vehicle there will be the originally installed tire size, load rating, and tire pressure for the front and rear tires.
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