Load Index Calculator

Introduction

The Tire Load Index Calculator is a weight engineering tool that calculates the maximum weight a single tire can support and helps you select tires appropriate for your vehicle's total weight. The Load Index is a number on the tire sidewall; it's not just a random figure but a metric indicating the tire's internal structure and rigidity. Using tires with an inappropriate load index is a primary cause of tire failure or abnormal wear during driving.

How It Works

When you enter a load index (e.g., 91, 105), the system consults ISO standard load tables to output the exact weight (kg and lbs) the tire can support at maximum inflation. In reverse mode, you can enter the vehicle's axle weight or total weight, and it will automatically find the minimum load index needed to safely support it. It also considers the differences between Standard Load (SL) and Extra Load (XL) and analyzes the correlation with the speed symbol for comprehensive safety info.

Usage Scenarios

• When switching tires on heavy vehicles like Electric Vehicles (EVs) due to battery weight, verify if standard internal combustion tires are sufficient or if high-load index specialized tires are mandatory.
• For RV conversions or cargo trucks carrying heavy loads, calculate the actual load per tire to get a minimum load index guideline to prevent blowouts.
• If you like a specific tire brand but the load index for your size is lower than stock, use this to engineeringly judge if it's within a safe allowable range or poses an overload risk.

How to Use the Load Index Calculator

In Lookup mode, enter a Load Index (60–120) to see the max load capacity in kg and lbs.

In Reverse mode, enter a target weight to find the minimum Load Index that can support it.

The reference table shows all standard LI values. Always choose a tire with LI equal to or higher than your vehicle's OEM specification.

In-Depth Guide

The load index is a coded number mapping to a maximum load per tire on the ISO/ETRTO table. Worked values: 91 = 615 kg, 95 = 690 kg, 100 = 800 kg, 105 = 925 kg. The scale is non-linear, rising about 3% per step, so each higher number supports progressively more weight; four tires rated 95 give a theoretical 4 × 690 = 2,760 kg of total support at the tire's rated pressure.

The speed rating letter sits next to the load index and caps the tire's sustained safe speed: H = 210 km/h, V = 240 km/h, W = 270 km/h, Y = 300 km/h (and the older T = 190, S = 180). A common mistake is fitting a lower speed rating than the vehicle's specification — even if you never reach that speed, the rating reflects construction and heat capacity, and many regions legally require meeting or exceeding the placard rating.

Never fit tires with a load index below the vehicle placard, and add margin for heavy or towing duty; Extra Load (XL) tires carry a higher index than Standard Load only when inflated to their higher reference pressure, so the rating is conditional on correct inflation. Heavier EVs and loaded trucks often need XL or LT tires specifically because the standard passenger index would be exceeded at the corner with the highest static and dynamic load.