Tyre load ratings: reading the sidewall

What the numbers on your tyre mean, how the load index converts to kilograms, why the placard sets a minimum, and what that means when you tow.

Facts checked

The code on the sidewall

Every road tyre carries its size and its service description on the sidewall. Take a common 4WD size:

265/65R17 112S

Part Meaning
265 Section width, in millimetres
65 Aspect ratio: the sidewall height is 65% of the width, about 172 mm here
R Radial construction
17 Rim diameter code: fits a 17-inch (432 mm) rim
112 Load index: 1,120 kg per tyre
S Speed symbol: 180 km/h

The load index and speed symbol always sit together, straight after the size. In short form, 94H means a load rating of 94 and a speed rating of H.

The load index is a code, not a weight

The number is not kilograms. It is an index into a table set out in the Australian Design Rules: ADR 23 for passenger car tyres and ADR 96 for light truck and commercial tyres. Each index means the most one tyre can carry when used as its manufacturer specifies.

Load index kg per tyre Load index kg per tyre
100 800 117 1,285
104 900 118 1,320
108 1,000 119 1,360
110 1,060 120 1,400
112 1,120 121 1,450
113 1,150 122 1,500
115 1,215 123 1,550
116 1,250 126 1,700

The scale is not a straight line. Going from 100 to 110 adds 260 kg. Going from 116 to 126 adds 450 kg.

Because the figure is per tyre, it is the axle that matters. Two 112-rated tyres on one axle carry at most 2,240 kg between them. That has to cover everything on that axle, including the extra a caravan puts on your rear axle through the tow ball. See front and rear axle limits.

Speed symbols

The letter after the load index, S in the example above, is the highest speed the tyre is rated to sustain: N is 140 km/h, S 180 km/h, T 190 km/h and H 210 km/h. Note that H sits between U (200) and V (240), not in alphabetical order.

The placard sets a minimum

Those two codes are what the rules check. Every passenger car built after 1972 carries a tyre placard listing the tyres and rims the manufacturer approved. It is usually on the door jamb of the driver's or front passenger's door, sometimes in the glovebox or on the fuel filler lid, and lists the recommended pressures, including for towing.

The placard is a floor, not a menu of exact choices. Under VSB14, a light vehicle under 4.5 t GVM may run tyres not listed on its placard provided:

A tyre can be rated higher than the placard: fitting tyres that exceed the manufacturer's load rating is allowed. What you cannot do is go lower. Fitting tyres with a lower load index than the placard's minimum does not meet that requirement, even if the tyre is the right size.

If a vehicle's GVM has been re-rated, VSB14 says its tyres must be able to carry the new GVM, both in total and on each axle. See GVM upgrades.

LT and passenger tyres

Light truck tyres come under a different design rule, ADR 96 (the source of the load index table above from 121 up), and are marked LT before the size, or C or LT after the rim size. Some show two load indices, such as 121/118: the first for a single tyre, the second for each tyre in a dual (twin) pair.

Fitting passenger tyres to a light goods vehicle that came with LT tyres has an extra rule. VSB14 says the load rating must be based on the highest individual wheel load, multiplied by 1.10. That is a 10% margin on the heaviest-loaded wheel, not just the placard figure.

Pressure and load

A tyre's load rating assumes it is inflated correctly: the load index is the heaviest load the tyre can manage at the correct pressure. Your placard, as above, or your owner's manual gives the pressures.

This is also why some owner's manuals list a towing speed limit. The international tyre fitment rule that the ADRs accept for some passenger vehicles lets a car's rear tyres be loaded up to 15% over their rating when towing, but only if the owner's manual gives a maximum towing speed, no more than 100 km/h, and a rear tyre pressure at least 20 kPa above normal. If your manual lists towing pressures or a towing speed, that is what they are for. Road speed limits when towing are separate, and set by each state; see state towing rules.

Tyre capacity is also one of the towing limits Transport for NSW lists. A caravan's loaded mass must not exceed the tyres' maximum rated carrying capacity, as well as the towbar, vehicle and ATM limits. The lowest of those is the one that applies, as the 3,500 kg towing capacity myth explains.

Trailer tyres

Trailers have tyre ratings too. VSB1, the national bulletin for trailers up to 4.5 t ATM (see ATM vs GTM), says:

Tyres age as well as wear, whatever their rating. The Victorian checklist says tyres over six years old, spares included, should be inspected by a tyre specialist, and tyres over ten years old replaced even if they look fine. The date code on the sidewall tells you a tyre's age: 4022 means week 40 of 2022. Check the caravan's tyres and its spare when you check the car's.

Common questions

What does 112S mean on a tyre?

112 is the load index: 1,120 kg per tyre. S is the speed symbol: 180 km/h. The example at the top of this page decodes the whole marking.

Can I fit tyres with a lower load index than the placard?

Not under VSB14. As in the placard section above, replacement tyres on a light vehicle must have a load rating no lower than the lowest on the tyre placard. A higher rating is allowed.

Do I need LT tyres to tow a caravan?

None of the sources we checked says so. Your tyres must meet the placard's minimum load and speed ratings. If your vehicle came with LT tyres and you switch to passenger tyres, VSB14 adds the 10% margin over the heaviest wheel load described above.

What tyre pressure should I use when towing?

Use the towing or full-load figure on your placard or in your owner's manual, as covered above. Never exceed the maximum pressure on the tyre's sidewall.

Sources

Authorities

Motoring associations (advice)