Tire Load Index, Load Range and Speed Ratings Explained

The short answer: what the tire load index means

The tire load index is a number printed on the sidewall, usually right after the tire size, that stands for the maximum weight one tire can carry when it is inflated to its specified pressure. The number is a code, not a weight. A load index of 91, for example, corresponds to 615 kg (about 1,356 lb) per tire. Multiply that figure by the number of tires on the vehicle to get the tire set's combined maximum capacity.

Two conditions change what that number means in practice. First, the rated load applies only at the inflation pressure the tire standard uses as its reference. At lower pressures the tire carries less. Second, the vehicle manufacturer's requirement on the tire placard or in the owner's manual sets the minimum load index the vehicle needs. A tire's own rating does not make it suitable for every vehicle it physically fits.

Where the codes appear on the sidewall

On most passenger car tires, the load index and speed rating appear together as the service description, immediately after the size. In the example below, 94 is the load index and W is the speed rating. XL marks an extra-load (reinforced) construction.

225/45R17 94W XL

225  section width in millimetres
45   aspect ratio (sidewall height as % of width)
R    radial construction
17   rim diameter in inches
94   load index  -> 670 kg (about 1,477 lb) per tire
W    speed rating -> 270 km/h (168 mph)
XL   extra load / reinforced

Light truck (LT) tires often show two load index numbers separated by a slash, such as 121/118. The first number applies when the tire is mounted singly. The second applies when it runs in a dual-wheel pair, where each tire is rated for a little less load. LT tires also carry a load range letter, covered below.

How the load index works and what it means in use

A tire carries weight mainly through the air pressure inside it, with the casing (the internal structure of cords and rubber) containing that pressure. More air pressure supports more load, but only up to the limit of the casing's strength. The load index records the load the tire is designed to carry at its reference pressure. Above that load, or below that pressure, the sidewalls flex more with each revolution. Extra flexing builds heat, and heat is what damages tire structure and can lead to failure.

The index scale is not linear, and the gaps between steps get larger as the numbers rise. A difference of one or two index points can mean a modest weight change at the low end of the scale and a larger one at the high end. Always look up the actual value instead of estimating from the number alone. Selected values from the standard table:

Load index | Max load per tire (kg) | Approx. (lb)

70 | 335 | 739

75 | 387 | 853

80 | 450 | 992

85 | 515 | 1,135

90 | 600 | 1,323

91 | 615 | 1,356

94 | 670 | 1,477

95 | 690 | 1,521

100 | 800 | 1,764

105 | 925 | 2,039

110 | 1,060 | 2,337

115 | 1,215 | 2,679

120 | 1,400 | 3,086

In use, the load index matters most when a vehicle runs near its weight limits: carrying passengers and cargo, towing, or using a roof load. Gross vehicle weight is not spread evenly, so one axle may carry much more than the other. That is why the vehicle manufacturer specifies a minimum load index based on the heaviest expected axle load, not on the curb weight divided by four.

Standard load, extra load and reference pressures

Passenger tires are made in standard load (SL, often unmarked) and extra load (XL, sometimes marked Reinforced or RF) versions. An XL tire has a stronger casing and a higher load index than an SL tire of the same size. It reaches that higher capacity only when inflated to a higher pressure. Under the European (ETRTO) convention widely used for metric passenger tires, the reference pressure is commonly 2.5 bar (about 36 psi) for SL and 2.9 bar (about 42 psi) for XL. Consult the tire manufacturer's load and inflation tables for the exact figures that apply to a specific tire.

An XL tire fitted to a vehicle that specifies SL tires does not automatically need more pressure. It must carry at least the load the vehicle requires at the pressure being used. Matching load capacity across different tire types requires load-inflation tables from the tire maker or a tire professional. The general tables above cannot answer that question.

What a tire load range is and how it differs from the load index

Load range is a letter rating used mainly on light truck tires in the US system. It describes the casing strength and the maximum inflation pressure the tire is built for. The letters replaced the older ply rating, which counted the cotton cord layers in early bias tires. Modern tires use fewer, stronger plies, so the ply rating is now only an equivalent strength figure. It does not count actual layers.

Load range | Ply rating equivalent | Typical max pressure (LT tires)

B | 4 | 35 psi

C | 6 | 50 psi

D | 8 | 65 psi

E | 10 | 80 psi

F | 12 | 95 psi

The two ratings work together. The load range tells you how much pressure the casing can hold. The load index tells you how much weight the tire carries at its rated pressure. A higher load range lets a tire of a given size run at higher pressure and therefore carry more weight, which shows up as a higher load index. The maximum pressure and maximum load molded into the sidewall of the specific tire take precedence over any generic table, including the typical figures above.

When a P-metric (passenger) tire is fitted to a light truck, SUV or van, US industry standards (from the Tire and Rim Association) apply a derating: divide the tire's rated load by 1.10. Its usable capacity is therefore lower than the sidewall figure suggests. This is one reason light trucks that specify LT tires should not be fitted with passenger tires without checking the reduced capacity against the vehicle's requirement.

What a tire speed rating means

The speed rating is the letter that follows the load index. It indicates the maximum speed at which the tire can carry its rated load under the test conditions used to certify it. Like the load index, it is a code. The letters are not in strict alphabetical order: H sits between U and V because it was added to the system later.

Speed rating | Maximum speed (km/h) | Approx. (mph)

L | 120 | 75

M | 130 | 81

N | 140 | 87

P | 150 | 93

Q | 160 | 99

R | 170 | 106

S | 180 | 112

T | 190 | 118

U | 200 | 124

H | 210 | 130

V | 240 | 149

W | 270 | 168

Y | 300 | 186

Tires rated above 300 km/h show the Y rating in parentheses, as in (Y). Older and some current high-performance tires use ZR inside the size designation, such as 245/40ZR18. ZR indicates a capability above 240 km/h (149 mph); the full service description, where present, gives the specific rating.

Limits of the speed rating

Speed ratings come from controlled laboratory tests on a correctly inflated, undamaged tire carrying a defined load. On the road, underinflation, overloading, wear, repairs, damage and high ambient temperatures all reduce how much speed and heat the tire can tolerate. The rating is a design limit under test conditions. It does not guarantee safe performance at that speed in real driving, and it does not override speed limits.

The speed rating also reflects construction choices that affect handling, so a higher letter is not simply better. Tires with higher ratings often use stiffer sidewalls and grippier compounds, which can mean a firmer ride and faster tread wear. Winter tires are commonly made with lower speed ratings than the summer or all-season tires they replace. Some vehicle manufacturers and jurisdictions have specific rules about this, so check the owner's manual and local regulations before fitting lower-rated winter tires.

Using these ratings when choosing replacement tires

The vehicle's tire and loading information placard, usually on the driver's door jamb in US vehicles, and the owner's manual give the original tire size, recommended cold inflation pressures and, typically, the original service description. As a general rule, replacement tires should match or exceed the original load index and speed rating.

• Load index: do not go below the original equipment figure. Capacity below the vehicle's requirement risks overloading the tires.
• Load range: on trucks and vans that specify LT tires, match the specified load range, and check the pressure the replacement tire needs to carry the required load.
• Speed rating: matching the original letter keeps the handling characteristics the vehicle was developed with. If a lower rating is fitted (for example, winter tires), the lower rating becomes the effective limit for the whole vehicle.
• Mixed fitments: keep the ratings consistent at least across each axle, and follow the vehicle maker's guidance for the full set.

Gaps and what to verify

Some details depend on information not covered here. Exact load capacity at pressures other than the reference pressure comes from each tire maker's load and inflation tables. The minimum ratings a particular vehicle needs depend on its model year, market, trim and equipment, and are set by the vehicle manufacturer. Rules on fitting lower speed-rated tires, including winter tires, vary by jurisdiction. Where a vehicle tows, carries heavy loads or uses non-original tire sizes, confirm the choice with the vehicle documentation or a qualified tire professional.