Tyre Weight Calculator

Estimate your vehicle's tyre load capacity with precision.

Tyre Load Index Values

Load Index	Max Load (kg) per Tyre	Max Load (kg) per Axle (Dual Wheels)

What is Tyre Weight Calculation?

The tyre weight calculator is a crucial tool for vehicle owners, fleet managers, and automotive enthusiasts to understand the load-bearing capabilities of their vehicle's tyres. It helps determine if the tyres installed on a vehicle can safely handle the weight it is designed to carry. This calculation is not just about fitting a tyre; it's about ensuring safety, performance, and longevity of both the tyres and the vehicle.

A proper tyre weight calculation ensures that the cumulative load capacity of all tyres on the vehicle is sufficient for its Gross Vehicle Weight (GVW). Overloading tyres can lead to catastrophic failures such as blowouts, uneven wear, reduced fuel efficiency, and compromised handling. Underutilizing tyre capacity might mean the tyres are over-specced for the vehicle's needs, potentially impacting ride comfort or cost.

Who should use it?

• Vehicle owners upgrading or replacing tyres.
• Fleet managers ensuring compliance and safety.
• Enthusiasts modifying vehicles (e.g., adding aftermarket accessories).
• Commercial vehicle operators transporting goods.
• Anyone concerned about vehicle safety and tyre condition.

Common Misconceptions:

• "Bigger tyres always mean more capacity": While tyre size matters, the load index is the specific rating. A large tyre with a low load index might not be suitable.
• "Vehicle manual is the only source": The manual provides GVW, but for tyre selection, the tyre's load index and speed rating are paramount. This calculator bridges that gap.
• "All tyres on a vehicle are the same": For safety and performance, all tyres on the same axle must be identical, and often, all tyres on the vehicle should match specifications.

Tyre Weight Calculation Formula and Mathematical Explanation

The core of the tyre weight calculation revolves around understanding the Load Index. The Load Index is a numerical code assigned to a tyre that indicates the maximum weight each tyre can support when properly inflated. However, this raw number needs context based on the vehicle's configuration.

The formula used in this calculator is a practical application derived from the tyre's Load Index and the vehicle's axle configuration:

Total Vehicle Load Capacity = (Load Index Value * 2) * Number of Tyres Per Axle * Number of Axles

Let's break this down:

• Load Index Value: This is the numerical value from the tyre's sidewall. Each Load Index corresponds to a specific maximum load capacity in kilograms (kg). For example, a Load Index of 100 typically means 800 kg per tyre.
• Load Capacity per Tyre: We first convert the Load Index to its actual weight capacity. A common standard is that the Load Index value multiplied by 2 gives an approximate weight in kg (e.g., Load Index 100 = 800 kg). This gives us the maximum weight one tyre can carry.
• Total Axle Capacity: This is calculated by multiplying the 'Load Capacity per Tyre' by the 'Number of Tyres Per Axle'. For standard vehicles, this means multiplying by 2. Some heavy-duty vehicles use dual wheels (two tyres on each side of an axle), so 'Tyres Per Axle' would be 4 in that context.
• Total Vehicle Capacity: Finally, we multiply the 'Total Axle Capacity' by the 'Number of Axles' to get the maximum weight the entire set of tyres can safely support.

Variables Explanation

Here's a table detailing the variables used in our tyre weight calculation:

Variable	Meaning	Unit	Typical Range / Options
Vehicle Gross Weight	The maximum operating weight of the vehicle as specified by the manufacturer.	kg	100 – 40,000+ (depends on vehicle type)
Tyre Load Index	A code indicating the maximum load a tyre can carry.	Unitless (Index)	40 – 126+ (e.g., 90, 98, 100, 104, 110)
Tyres Per Axle	The number of tyres fitted to a single axle (e.g., 2 for standard cars, 4 for dual-wheel trucks).	Count	1, 2, 3, 4
Number of Axles	The total count of axles on the vehicle.	Count	1 – 10+ (e.g., 2 for cars, 3-5 for trucks)
Load Capacity per Tyre	The maximum weight one tyre can support at its rated pressure.	kg	Derived from Load Index (e.g., 600 kg – 1000 kg for common indices)
Total Axle Capacity	The combined load capacity of all tyres on a single axle.	kg	Derived (e.g., 1200 kg – 4000 kg for dual wheels)
Total Vehicle Capacity	The maximum total weight the vehicle's tyres can safely support.	kg	Derived (e.g., 2400 kg – 40,000+ kg)

Practical Examples (Real-World Use Cases)

Let's explore how the tyre weight calculator works with real scenarios:

Example 1: Standard Family SUV

Consider a typical family SUV with the following specifications:

• Vehicle Gross Weight: 2,800 kg
• Tyre Size: P265/65R17
• Tyre Load Index: 112 (Found on the sidewall)
• Tyres Per Axle: 2
• Number of Axles: 2

Using the tyre weight calculator:

1. Vehicle Weight: 2800 kg
2. Tyre Load Index: 112
3. Tyres Per Axle: 2
4. Number of Axles: 2

Calculation Breakdown:

• Load Index 112 corresponds to 1120 kg per tyre.
• Total Axle Capacity = 1120 kg/tyre * 2 tyres/axle = 2240 kg per axle.
• Total Vehicle Capacity = 2240 kg/axle * 2 axles = 4480 kg.

Result Interpretation: The SUV's tyres, with a load index of 112, can support a total of 4480 kg. This is significantly higher than the vehicle's Gross Weight of 2800 kg, indicating the tyres are adequately rated for this vehicle under normal operating conditions. This provides a safety margin.

Example 2: Heavy-Duty Pickup Truck

Now, let's look at a heavy-duty pickup truck intended for towing and hauling:

• Vehicle Gross Weight: 3,500 kg
• Tyre Size: LT275/70R18
• Tyre Load Index: 121 (Often higher for Light Truck/LT tyres)
• Tyres Per Axle: 2
• Number of Axles: 2

Using the tyre weight calculator:

1. Vehicle Weight: 3500 kg
2. Tyre Load Index: 121
3. Tyres Per Axle: 2
4. Number of Axles: 2

Calculation Breakdown:

• Load Index 121 corresponds to 1450 kg per tyre.
• Total Axle Capacity = 1450 kg/tyre * 2 tyres/axle = 2900 kg per axle.
• Total Vehicle Capacity = 2900 kg/axle * 2 axles = 5800 kg.

Result Interpretation: The heavy-duty truck's tyres, rated at Load Index 121, can support a total of 5800 kg. This capacity is well above the vehicle's GVW of 3500 kg, ensuring safety even when towing heavy loads or carrying significant payload. The higher load index is critical for these applications. Always ensure the selected tyres meet or exceed the vehicle manufacturer's specifications.

How to Use This Tyre Weight Calculator

Using our tyre weight calculator is straightforward and takes just a few minutes. Follow these steps to get accurate results:

1. Identify Your Vehicle's Gross Weight (GVW): This is the maximum weight your vehicle is designed to carry, including passengers, cargo, and the vehicle itself. Check your vehicle's owner's manual or the compliance plate (often found on the doorjamb or under the hood). Enter this value in kilograms (kg) into the 'Vehicle Gross Weight' field.
2. Find Your Tyre's Load Index: Look at the sidewall of your current tyres. You'll see a series of numbers and letters (e.g., P265/65R17 112T). The number just before the speed rating letter (like T, H, V) is the Load Index. Enter this numerical value into the 'Tyre Load Index' field.
3. Determine Tyres Per Axle: Count how many tyres are fitted to a single axle. For most cars and SUVs, this is 2. For vehicles with dual rear wheels (often called 'duallies'), this would be 4. Select the appropriate number from the 'Tyres Per Axle' dropdown.
4. Count the Number of Axles: Determine the total number of axles your vehicle has. Standard cars have 2 axles. Larger trucks can have 3, 4, or more. Enter this number into the 'Number of Axles' field.
5. Click 'Calculate': Once all fields are filled, press the 'Calculate' button.

How to Read Results:

The calculator will display:

• Main Result (Total Vehicle Capacity): The maximum weight your installed tyres can safely support in kilograms (kg).
• Load Capacity per Tyre: The maximum weight a single tyre can support.
• Total Axle Capacity: The maximum weight both tyres on a single axle can support.
• Formula Explanation: A clear description of how the results were derived.
• Visual Chart: A bar chart comparing your vehicle's GVW against the total tyre capacity.
• Load Index Table: A reference table showing common load indices and their corresponding kg ratings.

Decision-Making Guidance:

Compare the Total Vehicle Capacity result with your vehicle's Gross Vehicle Weight.

• If Total Vehicle Capacity > Gross Vehicle Weight: Your current tyres have sufficient load capacity, offering a safety margin.
• If Total Vehicle Capacity = Gross Vehicle Weight: Your tyres are rated exactly for your vehicle's maximum weight. Consider tyres with a higher capacity for added safety, especially if you frequently carry heavy loads or tow.
• If Total Vehicle Capacity < Gross Vehicle Weight: Your tyres are overloaded. This is a critical safety issue. You MUST replace your tyres with ones that have a higher Load Index immediately.

This tool is essential for anyone performing a tyre size comparison or ensuring their vehicle is road-legal and safe.

Key Factors That Affect Tyre Weight Results

While the tyre weight calculation is primarily based on the Load Index and vehicle configuration, several other factors are crucial for a complete understanding of tyre safety and performance:

• Tyre Pressure: This is arguably the most critical factor. The Load Index rating is valid only at the tyre's maximum recommended pressure (often indicated on the tyre sidewall or vehicle door jamb). Under-inflation drastically reduces a tyre's load capacity and can lead to overheating and failure. Always check and maintain correct tyre pressures.
• Tyre Condition and Age: Old, worn, or damaged tyres (cracks, bulges, cuts) cannot achieve their rated load capacity safely. Even if the Load Index is high, a compromised tyre is a hazard. Check for tread depth and any signs of degradation.
• Ambient Temperature: Extreme heat can increase tyre pressure and stress the tyre's structure, potentially affecting its load-bearing capability and increasing the risk of failure. This is particularly relevant for heavy loads or high-speed driving in hot climates.
• Road Conditions: Rough terrain, potholes, or debris can damage tyres and wheels, compromising their integrity and ability to handle their rated load. Driving cautiously on poor surfaces is vital.
• Speed: Tyres have a speed rating associated with their Load Index. Driving consistently at or above the tyre's speed rating, especially under load, can generate excessive heat and reduce the effective load capacity.
• Load Distribution: While the calculator provides total capacity, how weight is distributed matters. Uneven loading can put excessive stress on specific tyres or axles, even if the total vehicle weight is within limits. Proper load balancing is key for safety and tyre life.
• Tyre Type (e.g., Standard, LT, XL): Extra Load (XL) or Light Truck (LT) tyres are specifically designed for higher load capacities than standard passenger car tyres. The calculator relies on the Load Index provided, but understanding the tyre's intended application is also important. An LT tyre with the same Load Index as a standard tyre might have a different construction supporting heavier duty use.

Frequently Asked Questions (FAQ)

Q: What is the difference between Load Index and Gross Vehicle Weight (GVW)?

A: The Gross Vehicle Weight (GVW) is the maximum total weight your vehicle is designed to carry (vehicle itself + passengers + cargo). The Load Index is a code on the tyre indicating the maximum weight that single tyre can support. The total load capacity of all tyres (calculated using the Load Index) must meet or exceed the GVW.

Q: Where can I find my tyre's Load Index?

Look at the sidewall of your tyre. It will have a series of numbers and letters like P215/60R16 95H. The number before the last letter (in this case, 95) is the Load Index.

Q: My car has a spare tyre. Should I include it in the tyre weight calculation?

No, the calculation is based on the tyres currently mounted on the vehicle's axles. The spare tyre's capacity is relevant for emergency use but not for the vehicle's operational load capacity.

Q: Can I mix tyres with different Load Indices on my vehicle?

It is strongly recommended not to mix tyres with different Load Indices, especially on the same axle. For safety and handling, tyres on the same axle should always be identical. Mismatched tyres can lead to uneven wear, poor handling, and compromised safety. If replacing tyres, ensure all four match the original specifications or are upgraded equally.

Q: What happens if my vehicle's weight exceeds the tyre's total capacity?

This is a serious safety hazard. It significantly increases the risk of tyre overheating, structural failure, and sudden blowout. This can lead to loss of control of the vehicle. You must replace the tyres with ones having a higher Load Index.

Q: Does a higher Load Index affect ride comfort?

Often, yes. Tyres with higher Load Indices may have stiffer sidewalls to support greater weight. This can result in a firmer ride compared to tyres with lower Load Indices. When choosing new tyres, consider balancing load requirements with desired comfort levels.

Q: Is it okay to use a tyre with a Load Index higher than required?

Generally, yes. Using a tyre with a higher Load Index than specified provides an increased safety margin. However, ensure the tyre's overall dimensions (diameter, width) are compatible with your vehicle and that all tyres on the same axle match.

Q: How does the number of axles and tyres per axle affect the calculation?

Each tyre carries a portion of the vehicle's weight. The total load capacity is the sum of each tyre's individual capacity. Therefore, more axles and more tyres per axle (like dual wheels) distribute the vehicle's weight over a larger surface area and more tyres, increasing the overall load-handling capability. Our tyre load calculator accounts for this distribution.