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Carbon Black for Tires

Choosing carbon black for tires means choosing a structural component, not a filler. Tread, carcass, sidewall and inner liner each call for their own grade; abrasion resistance, heat build-up and rolling resistance are set directly by that choice.

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New tire coming out of an opened curing mold in a tire factory

Roughly a quarter of a tire's weight is carbon black, and that ratio is no accident. Rubber alone can never provide the required abrasion resistance, tensile strength and tear resistance; these properties come from the physical and chemical bonds that carbon black forms with the polymer chains. That is why, in the tire industry, carbon black is referred to not as a filler but as a reinforcing agent.

A different grade for each layer

A modern radial tire is not made of a single rubber compound. Each layer has a different function, and that difference is reflected directly in grade selection:

  • Tread: The layer that contacts the road and wears. High-surface-area, high-structure hard grades are used: N220, N234, N339, N121. These grades deliver maximum abrasion resistance; the price is higher heat build-up (hysteresis) and therefore higher rolling resistance.
  • Subtread: An intermediate layer where heat management is critical. Low-hysteresis grades such as N375 are preferred.
  • Carcass and body plies: Layers that carry structural integrity and do not wear. Soft grades (N550, N660) provide sufficient reinforcement with low heat build-up.
  • Sidewall: A layer that flexes continuously and is exposed to ozone and UV. Medium-low-structure grades such as N660 strike the balance between fatigue resistance and flexibility.
  • Inner liner: The butyl rubber layer that keeps the tire airtight; low-surface-area grades are used here.

Three parameters that drive the choice

Iodine adsorption number (ASTM D1510) is an indirect measure of particle size. The higher the number, the smaller the particle, the larger the surface area and the stronger the reinforcement; at the same time, the compound becomes harder to process and heat build-up increases.

Oil absorption number (OAN, ASTM D2414) measures structure. High structure means higher modulus, better dispersion and easier extrusion in the compound.

Tint strength (ASTM D3256) shows whether the particle size distribution is narrow or broad; it is one of the best indicators of batch-to-batch consistency.

Why continuity of supply is critical

Changing a formulation is not cheap in tire production: when a new grade is introduced, compound settings, cure time and finished product tests are all repeated. For a tire manufacturer, continuity and batch consistency therefore matter as much as the supplier's price. That is why we provide an accredited laboratory certificate of analysis with every shipment.

What to Watch For in This Industry

Abrasion resistance and rolling resistance pull against each other

Raising abrasion resistance by increasing surface area also raises hysteresis loss and fuel consumption. In production that targets a tire label rating, this balance must be set from the start.

Dispersion matters as much as grade selection

The right grade used with poor dispersion will not deliver the expected mechanical values. Mixing time, temperature and sequence should be reviewed whenever the grade changes.

Moisture and pellet hardness can change in transit

Heating loss (ASTM D1509) and pellet hardness (ASTM D5230) are affected by storage conditions. Store jumbo bags in a closed, dry area out of direct sunlight.

Sulfur content affects vulcanization

The sulfur content of carbon black (ASTM D1619) should be included in the sulfur balance of the formulation; it must not be overlooked, especially in low-sulfur systems.

N330 Hard grade N330 carbon black is the most widely used general-purpose grade in the industry. It… Iodine g/kg 82 ± 5 OAN ml/100g 102 ± 5 N339 Hard grade N339 carbon black is a high-structure, high-modulus hard grade. It offers excellent… Iodine g/kg 90 ± 5 OAN ml/100g 120 ± 5 N326 Hard grade N326 carbon black is a low-structure, low-modulus hard grade with high elongation at… Iodine g/kg 82 ± 5 OAN ml/100g 72 ± 5 N234 Hard grade N234 carbon black combines high structure and high modulus. It delivers superior abrasion… Iodine g/kg 120 ± 5 OAN ml/100g 125 ± 5

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Trial program

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Test the product and return it if you are not satisfied. No obligation.

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Industry-Specific Questions

Which carbon black grade is used for tire treads?

The most common grades in passenger car treads are N330, N339 and N234. N121 and N220 are preferred in high-performance and racing tires. N220 and N299 stand out in truck and bus treads. The choice depends on the balance between target wear life and rolling resistance.

What is the difference between N330 and N339?

Their iodine adsorption is similar (N330: 82 g/kg, N339: 90 g/kg), but N339 has a markedly higher structure (OAN 120 vs 102 ml/100 g). This gives N339 higher modulus, better extrusion behavior and higher abrasion resistance. N330 processes more easily and is the more common general-purpose choice.

Why are soft grades used in the carcass?

The carcass does not wear; its job is to carry structural loads and maintain dimensional stability. A high-surface-area grade would generate unnecessary heat here and increase cost. N550 and N660 provide the required reinforcement with low hysteresis.

How much do I need to change my formulation when I switch grades?

For a change within the same ASTM class (for example N330 » N339), small adjustments to oil and accelerator levels are usually enough. For a change across classes (hard » soft), mixing time and the cure curve should be re-evaluated. Our technical team supports you through the transition.

Can we take a sample and test it on our own line?

Yes. Our 1-pallet trial program is designed for exactly this: you test the product under your own production conditions, and if you are not satisfied, you return the rest of the pallet.

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