Tire sidewall & DOT date decoder

It’s a code for the maximum load one tyre can carry at the pressure specified for that load in the tyre standards. For example, load index 91 means 615 kg (about 1,356 lb) per tyre. Multiply by the number of tyres on an axle for that axle’s tyre capacity. It isn’t the vehicle’s weight rating, and the vehicle maker’s required load index is on the door-jamb placard or in the owner’s manual.

Both mean extra load (reinforced): the tyre is built to run at a higher pressure than a standard-load tyre of the same size, which gives it a higher maximum load. The higher load is only available at that higher pressure.

Look for “DOT” followed by a string of letters and numbers. The last four digits are the date code: the first two are the week, the last two the year. 2319 means week 23 of 2019. The full code may only be on one side of the tyre, so check both sidewalls.

Three-digit codes were used before 2000: two digits for the week and one for the year within a decade. The decade can’t be determined from the code, so the tyre is more than 25 years old.

Not quite. ZR in the size (225/45ZR17) marks a tyre rated above 240 km/h (149 mph). The service description after the size, such as 94W or 94Y, gives the specific rating. A ZR tyre without a service description is rated above 240 km/h with the exact maximum set by the tyre maker.

There isn’t a single rule. Some vehicle and tyre manufacturers publish age guidance, and tyres also age faster with heat, sunlight and long periods unused. Check the vehicle and tyre maker’s guidance and have older tyres inspected by a professional.