Car Tyre Load and Speed Ratings Explained

Direct answer: A car tyre's load rating (load index) is the maximum weight each tyre can support, while the speed rating (speed symbol) is the maximum speed the tyre is certified for. Both are moulded on the tyre sidewall and must meet or exceed your vehicle manufacturer's specifications (found on the tyre placard) to remain legal and safe in Australia.

What Do Tyre Load and Speed Ratings Mean?

The sidewall of every car tyre carries a service description, for example 91V. The number 91 is the load index, and the letter V is the speed symbol. They are defined by international standards (such as ETRTO, TRA, JATMA) and adopted in Australian regulations.

The load index is a numerical code corresponding to a maximum load in kilograms. It does not directly state kilograms; you need a chart to convert it. For example, load index 91 equals 615 kg per tyre. The tyre's maximum load capacity is always at the maximum cold inflation pressure indicated on the sidewall.

The speed symbol is a letter indicating the maximum speed at which the tyre can carry its maximum rated load. For instance, V = 240 km/h, H = 210 km/h, T = 190 km/h. The speed rating is not a recommendation to drive at that speed; it is a certification of the tyre's structural capability.

Why Tyre Load and Speed Ratings Matter

Fitting tyres with lower load or speed ratings than specified by the vehicle manufacturer compromises safety and is illegal in Australia. The tyres may overheat, suffer structural failure, or reduce vehicle stability, especially when fully loaded or at highway speeds.

Conversely, fitting tyres with higher ratings is generally acceptable, but may affect ride comfort, noise, and fuel consumption due to stiffer construction. The vehicle's handling was tuned for the original specification, so significant deviations should be considered carefully.

How to Find Your Vehicle's Required Ratings: The Tyre Placard

Every passenger vehicle in Australia has a tyre placard, usually located on the driver's door jamb, inside the glovebox, or on the fuel filler flap. It lists the tyre size, load index, and speed symbol (or minimum speed rating) specified by the manufacturer. This is the authoritative source for your car.

If the placard specifies a minimum speed rating (e.g., "H or higher"), you may fit a tyre with a higher speed symbol. The load index must be at least the specified number. Never fit a lower load index, even if the speed rating is higher.

Understanding Load Index: Maximum Tyre Load

The load index is a number from 0 to 279, each corresponding to a specific load in kilograms. Common passenger car indices range from about 75 (387 kg) to 110 (1060 kg). For example:

• Load index 88 = 560 kg
• Load index 91 = 615 kg
• Load index 94 = 670 kg
• Load index 98 = 750 kg

When replacing tyres, the load index must be equal to or greater than the original specification. A higher load index tyre has a stiffer casing and may provide sharper steering response but often a firmer ride.

Reading a Tyre Sidewall Example

Consider a tyre marked 205/55R16 91V. Here:

• 205 = section width in millimetres
• 55 = aspect ratio (sidewall height as % of width)
• R = radial construction
• 16 = rim diameter in inches
• 91 = load index (615 kg)
• V = speed symbol (240 km/h)

Some tyres may have an extra load (XL or Reinforced) marking, meaning they can carry more load at higher inflation pressure. An XL tyre may have a higher load index for the same size. Always follow the placard's load requirement and adjust pressure according to the vehicle manufacturer's recommendations for XL tyres if fitted.

Speed Rating Chart and Common Symbols

Speed symbols are alphabetic, with some exceptions. Below is a chart for common passenger car ratings:

The speed rating is determined by laboratory tests simulating high-speed running. A tyre's speed capability decreases if it is damaged, improperly repaired, or under-inflated.

Australian Tyre Requirements and Legalities

In Australia, tyres must comply with the Australian Design Rules (ADR 23 for passenger cars). The tyre placard is a legal requirement. Fitting tyres with lower load or speed ratings than specified is a defect and may void insurance. State and territory regulations may also impose penalties.

When buying new tyres, always check the full service description, not just the size. A tyre seller should ask about your vehicle and advise compatible ratings. If you are uncertain, consult the placard or the vehicle handbook.

Comparing Different Listings: A Practical Guide

When shopping for tyres, you may see multiple options with the same size but different load and speed ratings. Here's how to compare them against your priorities:

Step-by-Step Comparison Method

1. Note your requirements: From the placard, write down the required load index and minimum speed rating.
2. List each tyre's specifications: Create a shortlist with columns for brand, model, size, load index, speed symbol, price, and any additional features (e.g., run-flat, XL).
3. Check compliance: Eliminate any tyre with a load index lower than required or a speed symbol below the minimum. These are not legal or safe options, regardless of price.
4. Consider higher ratings: Tyres with a higher load index or speed rating are acceptable. They may offer more durability or performance margin but could ride firmer or cost more.
5. Assess your driving conditions: If you often carry heavy loads or tow, a higher load index might be beneficial. If you mostly drive in the city, the standard rating is fine; focus on comfort and noise.
6. Compare beyond ratings: Use independent tyre tests and reviews for wet grip, dry handling, noise, and wear. Ratings alone don't tell the whole story.
7. Check availability: Some listings may lack the load/speed rating. Contact the seller or check the manufacturer's website. Missing information is not a drawback; it's just incomplete data.

Example Comparison Table

Suppose your car requires 205/55R16 91V. You find three options:

In this example, Tyre C must be rejected. Tyres A and D meet the minimum; Tyre B exceeds it. The choice between A and B might come down to price, ride comfort, and load needs. Tyre D offers run-flat capability but may have a stiffer sidewall and higher cost.

Distinguishing Missing Information from Drawbacks

If a listing omits the load or speed rating, it does not mean the tyre is unsuitable. It might be an oversight. Ask the seller for the full sidewall markings or check the manufacturer's specification sheet. A genuine drawback is a rating that is lower than required; that is a hard stop.

Common Misconceptions

• "Higher speed rating means better handling." Not necessarily. Higher speed-rated tyres often have stiffer sidewalls and different tread compounds, which can improve steering response but may reduce ride comfort and wet grip in some conditions.
• "Load index only matters when fully loaded." The load index must support the maximum axle load at all times. Even with one occupant, the tyre must meet the placard requirement for safety margins.
• "XL tyres are always better." XL (extra load) tyres can carry more weight at higher pressures. They may be required for some vehicles but are not universally better; they can be heavier and harsher.

Conclusion

Understanding load and speed ratings is essential for safe and legal tyre replacement in Australia. Always refer to the tyre placard for your vehicle's minimum requirements. When comparing tyres, create a structured shortlist, verify compliance first, then weigh other factors like comfort, performance, and price. Remember that a higher rating is acceptable, but a lower one is not. If information is missing, seek it out rather than guessing. By following these steps, you can make an informed decision that balances safety, performance, and value.