Tire Load Index Calculator
Minimum tire load index from axle weight.
What it does
Tires carry axles two at a time, and load index codes how much each can hold. A 1,000 kg axle needs 500 kg per tire, which tables at LI 84 exactly, with LI 85 adding 15 kg of margin. Codes, not sizes, answer capacity questions.
The tool above runs the ETRTO table from LI 80 to 100. Enter the heavier axle weight and it prints per-tire kg, minimum LI, and the plus-one margin pick. Defaults show LI 84 with LI 85; a 1,230 kg axle needs LI 91 with LI 92.
Standards bodies publish the tables behind the codes. ETRTO manuals and Tire and Rim Association yearbooks carry load ratings with dimensions, while NHTSA TireWise defines index use with placard pressure rules. Harmonized open tables reproduce the same rows: 84=500 through 100=800.
Placards rule fitment over math. Replacement tires must meet or beat original capacity at placard pressure with matching speed symbols and rims; plus-one sizing adds safety where loads run near limits. Weigh loaded axles rather than guessing curb weights.
How to use
- Weigh axles; take the heavier GAWR.
- Enter the axle kg.
- Read per-tire kg first.
- Read minimum LI.
- Read plus-one for margin.
- Fit placard size and pressure.
Formula
- axle
- Heavier axle load (GAWR) in kg.
ETRTO/TRA table values (LI 84=500 through 100=800); NHTSA defines LI use with placard pressure rules.
Worked example
Example: 1,000 kg axle
Defaults: 1,000 kg axle.
- Input: 1,000 kg axle (heavier GAWR).
- Per tire: 1,000 / 2 = 500 kg.
- Table: smallest LI at/over 500 is LI 84.
- Plus-one: LI 85 at 515 kg for margin.
- Tool shows 500 kg/tire, LI 84, LI 85 margin.
Reference table
| LI | kg | LI | kg |
|---|---|---|---|
| 84 | 500 | 91 | 615 |
| 85 | 515 | 92 | 630 |
| 90 | 600 | 98 | 750 |
| 99 | 775 | 100 | 800 |
Limits
- Table LI 80-100 only; heavier needs a pro.
- Static loads; dynamics need margins.
- Speed, pressure, rim limits separate.
- Twin fitments differ.
Common mistakes
- Dividing total weight by 4 blindly.
- Using the lighter axle.
- Fitting under placard capacity.
- Ignoring pressure with new tires.
- Skipping plus-one near limits.
Try it yourself
Quick checks. Answers sit tucked under each question.
1,230 kg axle?
Per tire 1,230 / 2 = 615 kg. Min LI 91 (615 kg). Plus-one LI 92 (630 kg).
1,500 kg axle?
Per tire 1,500 / 2 = 750 kg. Min LI 98 (750 kg). Plus-one LI 99 (775 kg).
Questions
How is per-tire load figured?
Axle over 2. Here 500 kg per tire.
How is minimum LI figured?
Smallest LI at or over per-tire kg. Here LI 84 at 500 kg.
What is plus-one for?
Next LI above minimum: LI 85 at 515 kg here, 15 kg of margin.
What does LI 91 carry?
LI 91 carries 615 kg; four total 2,460 kg. Check 615 x 4.
Must I match the placard?
Yes. Replacement capacity must meet or beat placard at placard pressure; respect speed and rims.
Which axle do I weigh?
Yes. Use the heavier axle (GAWR); unloaded axles mislead.
Sources
- ETRTO Standards Manual (load capacities)
- Tire and Rim Association Publications (load ratings)
- NHTSA TireWise (index and placard rules)