Tire Load Index and Speed Rating: How to Read Them?
- Tire markings (e.g., 91V) combine a numerical load index and a speed rating letter, embossed on the sidewall
- The load index indicates the maximum weight supported per tire, not per vehicle
- The speed rating sets the maximum sustained speed, not a single momentary speed
- Thresholds vary depending on the application: car, motorcycle, winter, agricultural, or trailer tires
- Using indices lower than the original equipment is a non-compliance issue that could void your insurance
On a tire sidewall, immediately following the size (for example, 205/55 R16), a combination of numbers and letters like 91V provides two distinct pieces of information: the maximum load the tire can carry and the maximum continuous speed it can maintain. The number is the load index, and the letter is the speed rating. These two values are standardized and common across all brands: a tire marked 91 always supports 615 kg, regardless of the manufacturer. Understanding this helps prevent choosing undersized tires for your vehicle—a common error when replacing a single tire or changing sizes.
How to Read the Load Index
The load index is the number preceding the letter in the marking (91 in 91V). This is not a direct weight in kilograms; it is a code that refers to a value in a standardized lookup table used by all tire manufacturers. For example, index 91 corresponds to 615 kg, index 88 to 560 kg, and index 100 to 800 kg.
This figure represents the maximum load supported by a single tire, not per axle or the entire vehicle. To find the actual allowable load for your car, multiply this value by four (or the number of wheels on the ground) and compare it to the Gross Vehicle Weight Rating (GVWR) found on your vehicle registration or manufacturer label. A minivan loaded with luggage and passengers can easily approach its GVWR: choosing an insufficient load index causes premature tire wear, deforms the carcass, and increases the risk of a blowout due to heat buildup.
For agricultural and trailer tires, the reading changes slightly: two load indices are sometimes shown side-by-side (for example, 143/141), where the first is for single mounting and the second is for dual mounting. This is a specific feature and should not be mistaken for a labeling error.
How to Read the Speed Rating
The speed rating is the letter following the load index (V in 91V). Each letter corresponds to a maximum speed the tire can sustain under normal load and pressure conditions. A summary of the common table:
- Q = 160 km/h (often winter or 4×4 tires)
- S = 180 km/h
- T = 190 km/h
- H = 210 km/h
- V = 240 km/h
- W = 270 km/h
- Y = 300 km/h
This rating does not mean you can hit this speed in a single burst under any condition; it guarantees the tire’s structural integrity at this speed for an extended period at the rated load. Driving beyond the speed rating, even briefly, increases the tire’s internal temperature and can cause rubber delamination, which is often invisible from the outside until it fails.
On a motorcycle, the reading is identical, but the indices encountered are often higher (H, V, W, or even ZR for sportbikes exceeding 240 km/h) because the speed ranges used are different from those of a city car.
Where to Find the Marking on the Tire
The full marking is located on the tire sidewall, usually right after the size designation. A typical example: 205/55 R16 91V. Here, 205 is the width in mm, 55 is the aspect ratio, R16 is the rim diameter in inches, and 91V represents the load/speed rating. It is this sequence, often embossed and sometimes painted white at the factory, that you must know how to identify to read the tire index correctly before any purchase or technical inspection.
On a car, the tire load and speed rating always appears immediately after the rim diameter without a space: 91V, 94H, 88W… The number comes first, followed immediately by the letter. Be careful not to confuse this letter with the one that sometimes precedes the diameter (like the “R” for “radial” in 205/55R16), which has nothing to do with speed. For a motorcycle tire, the location is the same, but the values differ significantly: a 180/55 ZR17 73W, for example, often includes a speed index of Z or ZR (above 240 km/h) directly in the designation, in addition to the final 73W duo. Reading a motorcycle tire’s speed rating therefore requires checking both occurrences before concluding.
Some tires also display a second set of indices in parentheses, next to or below the main marking, such as 91V (94V). This second set corresponds to reinforced extra load use (Extra Load, often noted as XL) or a dual certification related to a specific application (such as original equipment manufacturer specs). Never confuse this second marking with the primary index used for daily driving: the first duo, outside of parentheses, always defines the maximum allowed load and speed for normal use.
On trailer tires and certain commercial tires, you will frequently find the mention of LT (Light Truck) or C (Commercial) just before the indices, such as 195/70 R15C 104/102R. The double number 104/102 indicates two distinct load indices here: the first for single mounting and the second for dual mounting—a nuance specific to trailer and commercial tire load and speed ratings that you won’t find on standard passenger car tires. This reinforced carcass (C or reinforced structure) supports higher loads than a standard tire of the same size.
For winter tires, the marking location remains the same, but the speed rating is often lower than the summer equivalent on the same vehicle (a T or H might replace a V or W). This reflects a rubber compound optimized for cold temperatures rather than high speeds; this is a key point to check regarding the winter tire load and speed rating when comparing references. On agricultural tires, the reading is different: the agricultural tire load and speed rating is presented in a similar format (for example, 149A8), where “A8” denotes a speed category specific to agricultural machinery, capped well below road standards and not to be interpreted using the standard passenger car table.
Finally, on a bicycle tire, the marking follows a different logic: reading bicycle tire indications primarily means identifying the ETRTO designation (e.g., 47-622) and the recommended pressure in bar or PSI; the automotive-style load and speed indices do not exist for this use.
Can You Install a Lower or Different Index?
Regulations allow you to install a load or speed rating higher than the original, but never lower. The vehicle manual or registration may sometimes specify an accepted range, but by default, you should refer to the label on the door jamb or fuel flap, which indicates the minimum required indices for each approved tire size.
Installing a lower speed rating (for example, a T instead of a V) is a non-compliance issue: in the event of an accident, even if there is no direct causal link to the tire, the insurer may cite this non-compliance to reduce or deny compensation. This point is often overlooked when buying used tires or cheaper winter tires, where the speed rating is sometimes intentionally lowered by the manufacturer because winter use does not require high speeds—this practice is only legal if it complies with the manufacturer’s recommendations for the season.
Specifics by Application (Car, Moto, Winter, Agricultural, Trailer)
Index thresholds vary significantly depending on the vehicle type and intended use, and confusing the tables is a common source of error.
For a passenger car, common load indices range from approximately 82 to 100, and speed indices range from S to Y depending on the vehicle’s power. On a motorcycle, load indices are generally lower (as weight per tire is distributed differently), but speed indices climb quickly, especially on sportbikes.
Winter tires often show a lower speed rating than their summer counterparts (Q or T instead of H or V), as they are not designed for high speeds and lose handling stability beyond their threshold; this is not a defect but a design suited to seasonal use.
Agricultural and trailer tires follow different logic: the maximum speed is often legally capped (e.g., 25 or 40 km/h for certain tractors), and the load index becomes the dominant criterion, sometimes featuring the two distinct values for single or dual mounting mentioned earlier.
How to read the load index and speed rating of a tire?
It is found on the tire sidewall, immediately following the size: a number (load index, which should be compared to a standardized table) followed by a letter (maximum sustained speed rating).
What does the index 91V mean on a tire?
91 corresponds to a maximum load of 615 kg per tire, and V corresponds to a maximum sustained speed of 240 km/h.
Can you drive with a speed rating lower than the original?
No, this is a non-compliance that can affect insurance coverage in the event of an accident, unless specifically recommended by the manufacturer (notably for winter tires).
Does the tire load index apply to the entire vehicle?
No, it indicates the maximum load supported by a single tire; it must be compared to the vehicle’s GVWR distributed across the number of wheels on the ground.
Are the load and speed indices different for a motorcycle?
The reading principle is the same, but motorcycles often show lower load indices and higher speed indices (H, V, W, ZR).
Why do winter tires often have a lower speed rating?
Because they are designed for grip in cold weather rather than high speeds; the index reflects this seasonal use and is not a defect.
Sources
- Michelin France – Tire load and speed indices
- Allopneus – Tire load and speed indices
- Centrale Pneus – Speed and load index, correspondence tables
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