Tire Capacity Margin Calculator
Compare the load on each tire with its rated capacity. See the reserve margin in kg, lb and percent, and flag overloaded tires.
Compare entered loads with applicable capacities.
Tire Capacity Margin Calculator: Tire Size Inputs
Compare two tire sizes here. Use the formulas and reference tables below for this tool's specific calculation.
How Tire Capacity Margin Calculator Works?
The Tire Capacity Margin Calculator works by subtracting the actual load on a tire from the tire's capacity at the pressure in use. The tool uses 3 steps.
Enter tire load
Type the load per tire from a scale ticket, for example 700 kg (1,543 lb).
Enter capacity
Type the load index (98 = 750 kg) or the capacity at the pressure in use.
Read the margin
The calculator returns +50 kg (+110 lb), a 6.7% margin, and flags a margin under 10% as low.
Tire Capacity Margin Calculator Formula
The Tire Capacity Margin Calculator formula is Margin = Capacity − Load, and Margin % = Margin ÷ Capacity × 100.
M = C − LM% = M ÷ C × 100U% = L ÷ C × 100- C
- Capacity at the pressure in use (kg)
- L
- Actual load on the tire (kg)
- U%
- Share of capacity used
Worked example
A rear tire carries 1,300 kg (2,866 lb), and the tire is rated 121 (1,450 kg, 3,197 lb). The margin is 150 kg (331 lb), or 10.3%. Utilization is 89.7%.
Tire Capacity Margin Calculator Conversion Table
The Tire Capacity Margin Calculator conversion table shows the reserve margin for 7 load and rating combinations.
| Load per tire | Rating | Margin | Margin (%) | Status |
|---|---|---|---|---|
| 560 kg (1,235 lb) | 94 = 670 kg | +110 kg (+243 lb) | +16.4% | OK |
| 625 kg (1,378 lb) | 94 = 670 kg | +45 kg (+99 lb) | +6.7% | Low margin |
| 700 kg (1,543 lb) | 98 = 750 kg | +50 kg (+110 lb) | +6.7% | Low margin |
| 800 kg (1,764 lb) | 101 = 825 kg | +25 kg (+55 lb) | +3.0% | Low margin |
| 1180 kg (2,601 lb) | 121 = 1450 kg | +270 kg (+595 lb) | +18.6% | OK |
| 1300 kg (2,866 lb) | 121 = 1450 kg | +150 kg (+331 lb) | +10.3% | OK |
| 640 kg (1,411 lb) | 91 = 615 kg | -25 kg (-55 lb) | -4.1% | Overloaded |
What is Tire Capacity Margin Calculator?
A Tire Capacity Margin Calculator is a tool that shows how much load capacity a tire has left after the vehicle's real load. A tire at or above 100% utilization overheats and wears fast.
Many fleet and RV guidelines target a reserve of at least 10% between actual load and capacity.
The capacity input needs to match the pressure in use. A tire at reduced pressure has less capacity than its load index states.
What are the uses of Tire Capacity Margin Calculator?
There are 4 main uses of the Tire Capacity Margin Calculator, including RV safety checks and trailer loading.
RV safety checks
Confirm each corner has enough capacity.
Trailer loading
Check trailer tires after loading.
Tire upgrades
Measure the margin gained from a higher index.
Fleet audits
Record tire utilization across vehicles.
Related Core Tire Dimensions Tools
View All 134 Subtools →Compare two tire sizes.
Compare several sizes together.
Estimate nominal overall diameter.
Calculate absolute and percentage differences.
Estimate nominal circumference.
Compare estimated rolling distances.