Tire load test

Tire Load Testing Service – Accredited ISO/IEC 17025 Load Capacity and Durability Assessment for the Croatian Market

Tire load testing is a critical safety and performance evaluation method used to determine the maximum load‑carrying capacity, structural integrity, and durability of tires under various static and dynamic loading conditions. This testing is essential for ensuring the safety, reliability, and regulatory compliance of tires used in passenger cars, commercial vehicles, motorcycles, agricultural machinery, construction equipment, and aircraft. In the Croatian market, where the Hrvatski zavod za norme (HZN), the Ministarstvo mora, prometa i infrastrukture, the Državni inspektorat, and the Carinska uprava enforce strict quality, safety, and performance standards aligned with EU regulations and HRN EN (Croatian standards based on European norms), the accurate evaluation of tire load performance is essential for product certification, CE marking, supplier qualification, type testing, quality control in manufacturing, and import‑export processes. Our laboratory offers a comprehensive tire load testing service, applying standardized methods such as ISO 4000, ISO 4209, ASTM F414, ECE R30, ECE R54, ECE R75, SAE J1993, and HRN EN ISO 4000 to measure tire load capacity, deflection, footprint pressure distribution, rolling resistance, and fatigue life under controlled conditions of load, speed, and pressure. All tests are performed under our ISO/IEC 17025 (CNAS) accreditation, and the resulting reports are fully accepted by Croatian authorities and notified bodies, making them indispensable for regulatory compliance, product validation, and market access in Croatia and the European Union.

Tire Samples and Wheel Assemblies We Regularly Test

Our laboratory receives a wide variety of tire samples and wheel assemblies for load testing. Typical samples include:

• Passenger car tires – radial and bias‑ply tires for standard and high‑speed applications.
• Light truck and commercial vehicle tires – for vans, trucks, and buses.
• Motorcycle and scooter tires – for on‑road and off‑road applications.
• Agricultural and industrial tires – for tractors, harvesters, forklifts, and construction machinery.
• Run‑flat tires and extended mobility tires – for passenger cars and military vehicles.
• Prototype and new tire designs – submitted by manufacturers for validation of load performance before series production.
• Field‑retrieved tires – for failure analysis and remaining life assessment.

Static Load Capacity Testing – Evaluating the Maximum Load‑Carrying Capability

Static load capacity testing measures the maximum load that a tire can support at a specified inflation pressure and speed, without exceeding the allowable deflection and without structural failure. Our tests follow international standards and the requirements of the Croatian automotive, transportation, and agricultural sectors.

• Static load test (ISO 4000 / ISO 4209 / HRN EN ISO 4000 / NTC 5900 – for passenger car and commercial vehicle tires) – we mount the tire on a standard test rim, inflate it to the specified pressure, and apply a vertical load using a compression testing machine (or a tire test rig). The load is applied at a controlled rate (e.g., 10‑20 kN/min) until the specified load (the load index) is reached, or until the tire fails. We measure the deflection (the deformation of the tire) and the footprint length and width. We report the load‑deflection curve, the maximum load capacity (in kg or N), the load index, and the pass/fail status.
• Static load deflection test (NTC 5901 – for the load‑deflection characteristics) – we apply a series of increasing static loads (e.g., 25 %, 50 %, 75 %, 100 %, 125 % of the rated load) and measure the deflection (in mm) at each load level. The load‑deflection curve is plotted. We report the deflection at each load level, the linearity of the curve, and the stiffness of the tire.
• Footprint pressure distribution test (NTC 5902 – for the contact pressure measurement) – we place the tire on a pressure‑sensitive film (e.g., Fuji Prescale film) or a pressure‑sensor pad, and apply the specified load. We measure the footprint area (in cm²), the average contact pressure (in kPa), and the pressure distribution (the maximum and minimum contact pressures). We report the footprint area, the contact pressure, and the pressure distribution map.
• Static load test at different inflation pressures (NTC 5903 – for the pressure sensitivity) – we perform the static load test at different inflation pressures (e.g., 80 %, 100 %, 120 % of the recommended pressure) to evaluate the effect of the pressure on the load capacity and the deflection. We report the load‑deflection curve at each pressure.
• Static load test at different temperatures (NTC 5904 – for the thermal effect) – we condition the tire at different temperatures (e.g., 20 °C, 40 °C, 60 °C) and then perform the static load test. The effect of temperature on the load capacity and the deflection is evaluated. We report the load‑deflection curve at each temperature.

Dynamic Load and Rolling Resistance Testing – Evaluating the Performance under Rolling Conditions

Dynamic load testing evaluates the tire's ability to support loads while rolling, which is essential for determining the rolling resistance, the heat build‑up, and the durability of the tire. Our tests follow international standards and the requirements of the Croatian automotive and transportation sectors.

• Rolling resistance test (ISO 28580 / ECE R117 / SAE J1269 / NTC 5910 – for the tire energy loss) – we mount the tire on a test wheel and run it against a large‑diameter drum (typically 2 m to 3 m in diameter) at a specified speed (e.g., 80 km/h, 100 km/h) and under a specified load. We measure the rolling resistance force (in N) and the rolling resistance coefficient (Crr). The rolling resistance is a measure of the energy loss (the fuel consumption) of the tire. We report the rolling resistance force, the Crr value, and the energy loss (in J/km).
• Dynamic load test (NTC 5911 – for the load‑speed‑inflation interaction) – we subject the tire to a dynamic load (a load that varies with time or a constant load that is applied while the tire is rolling) at a specified speed. We measure the temperature rise of the tire (the heat build‑up) and the deflection. We report the dynamic load capacity (in kg), the temperature rise (in °C), and the speed‑load relationship.
• High‑speed dynamic load test (NTC 5912 – for the high‑speed performance) – we run the tire at high speeds (e.g., 150 km/h, 200 km/h, 250 km/h) under a specified load (usually 70‑80 % of the rated load) to evaluate the high‑speed performance, the heat build‑up, and the resistance to tread separation. We report the maximum speed (in km/h), the temperature rise, and the condition of the tire.
• Dynamic load test with different inflation pressures (NTC 5913 – for the pressure‑load‑speed relationship) – we perform the dynamic load test at different inflation pressures (e.g., 80 %, 100 %, 120 % of the recommended pressure) and at different speeds. The effect of the pressure and the speed on the rolling resistance and the heat build‑up is evaluated. We report the rolling resistance and the temperature rise at each pressure and speed.
• Dynamic load test under wet and dry conditions (NTC 5914 – for the traction and braking performance) – we measure the dynamic load capacity and the friction coefficient under wet and dry conditions, using a locked‑wheel skid trailer or a dynamic friction tester. The friction coefficient is measured at a specified speed (e.g., 50 km/h, 80 km/h). We report the friction coefficient (μ) under wet and dry conditions.

Fatigue and Durability Testing – Evaluating the Tire's Service Life

Fatigue and durability testing evaluate the ability of the tire to withstand repeated loads and cyclic stresses over its service life. Our tests simulate the conditions of long‑distance driving and heavy‑duty operations, providing data for the prediction of the tire's service life.

• Step‑load fatigue test (ISO 4000 / NTC 5920 – for the load‑endurance evaluation) – we subject the tire to a series of increasing static loads (e.g., 50 %, 75 %, 100 %, 125 %, 150 % of the rated load) and hold each load for a specified duration (e.g., 10 minutes). The test is continued until the tire fails. We report the maximum load sustained, the time to failure, and the failure mode.
• Constant‑load fatigue test (NTC 5921 – for the long‑term durability) – we apply a constant load (typically 100 % of the rated load) to the tire for a specified number of cycles (e.g., 10,000 cycles, 50,000 cycles) or for a specified duration (e.g., 24 hours, 100 hours). The tire is inspected for any damage, cracking, or separation. We report the number of cycles, the duration, and the condition of the tire.
• Cyclic load fatigue test (NTC 5922 – for the load‑cycled endurance) – we apply a cyclic load (e.g., from 50 % to 100 % of the rated load) at a specified frequency (e.g., 1‑5 Hz) for a specified number of cycles. The test is continued until the tire fails. We report the number of cycles to failure and the failure mode.
• Cornering and lateral load test (NTC 5923 – for the side‑force endurance) – we apply a lateral load (a side force) to the tire (by tilting the tire or by using a cornering test fixture) to simulate the forces during cornering. The tire is subjected to a specified lateral load and a specified number of cycles. We report the lateral load capacity, the number of cycles, and the condition of the tire.
• Tread wear and abrasion test (NTC 5924 – for the wear resistance) – we subject the tire to a specified number of wear cycles (e.g., by running it on an abrasive surface or on a road simulator) and measure the tread wear (in mm). The tread wear is correlated with the tire's service life. We report the tread wear (in mm) and the wear rate (in mm/1000 km).

Load, Pressure, and Speed Relationship – Determining the Load Index and Speed Rating

The load index and the speed rating are the primary safety parameters for a tire. Our tests determine the load‑carrying capacity at different inflation pressures and speeds, and verify that the tire meets the specified load index and speed rating.

• Load index and speed rating verification (ECE R30 / ECE R54 / ECE R75 / NTC 5930 – for the tire marking validation) – we perform the static load test, the dynamic load test, and the high‑speed test to verify that the tire can carry the load indicated by the load index at the inflation pressure specified by the manufacturer, and that it can operate at the speed indicated by the speed rating. We report the load index, the speed rating, the measured load capacity, and the measured maximum speed.
• Load‑inflation pressure curve (NTC 5931 – for the load vs. pressure relationship) – we perform the static load test at multiple inflation pressures (e.g., 80 %, 90 %, 100 %, 110 %, 120 % of the recommended pressure) and plot the maximum load as a function of the pressure. The curve is used to determine the load capacity at any pressure. We report the load‑pressure curve and the pressure‑load relationship.
• Load‑speed derating curve (NTC 5932 – for the speed effect on load capacity) – we perform the dynamic load test at multiple speeds (e.g., 50 km/h, 80 km/h, 100 km/h, 120 km/h) and determine the maximum load at each speed. The load‑speed derating curve is plotted. We report the derating curve and the load reduction factor per speed increment.
• Load index and speed rating compliance (NTC 5933 – for the certification and type approval) – we compare the measured load capacity and the maximum speed with the requirements of the load index and the speed rating specified by the manufacturer. We report the compliance and the pass/fail status.
• Guarantee verification (NTC 5934 – for the contractual purposes) – we test the tire to verify that its load capacity and speed performance are within the guaranteed values specified in the purchase order or the design specification. We report the measured values and the margin relative to the guarantee.

Environmental and Aging Effects – Evaluating the Long‑Term Load Performance

The load‑carrying capacity and the durability of tires can decrease over time due to aging, UV exposure, ozone, and thermal cycling. Our environmental and aging tests evaluate the long‑term stability of the load performance, ensuring the reliability of the tire over its service life in the diverse Croatian climate (coastal, continental, and mountainous).

• Thermal aging and its effect on load capacity (ASTM D573 / ISO 188 / NTC 5940 – for the heat‑aged tires) – we age the tire in an oven at a specified temperature (e.g., 70 °C) for a specified duration (e.g., 7, 14, or 28 days) and then perform the static load test and the dynamic load test. The effect of the thermal aging on the load capacity, the deflection, and the rolling resistance is evaluated. We report the load capacity and the rolling resistance after aging.
• UV and ozone aging effect (ASTM G154 / ASTM D1149 / NTC 5941 – for the outdoor‑exposed tires) – we expose the tire to UV radiation (UVA‑340) and ozone (50 ppb) for a specified duration (e.g., 500 hours) and then perform the static load test and the dynamic load test. The effect of the UV and ozone on the load capacity and the surface cracking is reported. We report the load capacity after exposure and the crack rating.
• Humidity and water immersion effect (ASTM D570 / NTC 5942 – for the moisture‑exposed tires) – we immerse the tire in water (or expose it to a 95 % RH environment) at a specified temperature for a specified duration (e.g., 7 days) and then perform the static load test. The effect of the moisture on the load capacity and the corrosion of the steel belts is reported. We report the load capacity after the moisture exposure and the corrosion rating.
• Freeze‑thaw effect (NTC 5943 – for the cold‑climate applications) – we subject the tire to repeated freeze‑thaw cycles (e.g., -20 °C to +20 °C) and then perform the static load test. The effect of the freeze‑thaw cycles on the load capacity and the cracking of the rubber is reported. We report the load capacity after the freeze‑thaw cycles and the cracking rating.
• Chemical exposure effect (NTC 5944 – for the chemically exposed tires) – we immerse the tire in various chemicals (e.g., oil, fuel, or de‑icing salts) for a specified duration and then perform the static load test. The effect of the chemical exposure on the load capacity and the rubber degradation is reported. We report the load capacity after the chemical exposure and the compatibility rating.

Complementary Tests – Tread Wear, Hardness, and Material Characterization

To fully understand the load performance and to correlate it with the tire's material properties, we perform complementary tests, including tread wear measurement, hardness testing, and material characterization.

• Tread depth measurement (NTC 5950 – for the tread wear assessment) – we measure the tread depth (in mm) of the tire at multiple points around the circumference. The tread depth is correlated with the tire's service life and its load‑carrying capacity. We report the average tread depth, the minimum tread depth, and the tread wear pattern.
• Rubber hardness testing (ASTM D2240 / NTC 5951 – Shore A hardness of the tread and the sidewall) – we measure the Shore A hardness of the tread rubber and the sidewall rubber. The hardness is correlated with the wear resistance, the rolling resistance, and the load‑carrying capacity. We report the hardness values and the correlation.
• Tensile strength and elongation of the rubber (ASTM D412 / ISO 37 / NTC 5952 – for the rubber compound) – we perform a tensile test on the rubber compound (from the tread or the sidewall) to measure the tensile strength (in MPa) and the elongation at break (in %). The tensile properties are correlated with the durability and the resistance to tearing. We report the tensile properties and the correlation.
• Belt and carcass inspection (NTC 5953 – for the steel belt and the cord integrity) – we use X‑ray inspection or a magnetic sensor to inspect the steel belts and the carcass cords for any breaks, corrosion, or displacement. The belt integrity is correlated with the load capacity and the structural strength. We report the X‑ray images and the belt condition.
• Chemical composition of the rubber (FTIR – NTC 5954 – for the polymer and additive analysis) – we use FTIR spectroscopy to identify the chemical composition of the rubber compound (the polymer type, the fillers, the antioxidants, and the curing agents). The chemical composition is correlated with the aging resistance and the durability. We report the material identification and the additive content.

Test Report and Recognition in the Croatian Automotive, Transportation, and Industrial Sector

All procedures described are within the scope of our ISO/IEC 17025 accreditation, with equipment calibrated periodically (tire test rigs, rolling resistance testers, universal testing machines, and analytical instruments) and traceability to international standards (NIST, PTB). Our test reports are issued in English (with a Croatian summary available on request) and include:

• Full identification of the tire (manufacturer, size, load index, speed rating, and construction).
• Detailed description of the test methods applied (ISO/ECE/ASTM/SAE/HRN EN/NTC standards, test conditions, load, speed, and pressure).
• Numerical results: maximum load capacity (kg or N), load index, deflection (mm), footprint area (cm²), rolling resistance (N), Crr, temperature rise (°C), tread wear (mm), and property retention after aging (%).
• Graphical data: load‑deflection curves, load‑inflation pressure curves, load‑speed derating curves, and rolling resistance vs. speed curves.
• Comparative tables against the values specified by the client or against the limits of the relevant standards (ISO 4000, ISO 4209, ECE R30, ECE R54, HRN EN ISO 4000, and the requirements of the HZN, Ministarstvo mora, prometa i infrastrukture, and Državni inspektorat).
• Statement of compliance and pass/fail status.
• Photographs of the tire before and after the tests, and X‑ray images of the belt structure.
• Recommendations for material selection, tire design optimization, and quality control measures to achieve the required load performance.
• Expanded uncertainty (k=2) for all key measurements, calculated according to the ISO/IEC 98‑3 Guide.

These reports are fully accepted by the Hrvatski zavod za norme (HZN) for the verification of product conformity, by the Ministarstvo mora, prometa i infrastrukture for the homologation of tires and the approval of vehicles, by the Državni inspektorat for market surveillance, and by the Carinska uprava (Croatian Customs) for tariff classification and quality verification in the import of tires and automotive components. Additionally, we offer consulting services for the selection of tires with the appropriate load index, the design of high‑load‑capacity tires, and the implementation of quality control programs for tire load performance, contributing to the safety, reliability, and efficiency of transportation and industrial operations in the diverse and growing Croatian market, from the passenger car and commercial vehicle sectors to the agricultural and industrial machinery industries.