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Tire compound guide

# Tire compound guide

## What is a tire compound?

A tire compound is the mixture of rubber (natural and synthetic), fillers (carbon black or silica), plasticisers, vulcanisation agents, and other additives that determines how a tire performs. The most important compound property for seasonal behaviour is the glass transition temperature (Tg): winter compounds have a lower Tg (around −60°C) so they stay pliable below 7°C, while summer compounds have a higher Tg and harden in cold weather. The shift from carbon black to silica as the primary filler in the 1990s was the key technology that enabled A-grade wet braking and low rolling resistance to coexist in the same tire.

## What a tire compound is made of

A typical passenger car tire uses several distinct compound formulations across its structure: the tread compound (what contacts the road), the sidewall compound (ozone resistance, flex fatigue), the inner liner (air retention), and the shoulder compound. Each is optimised separately. The tread compound is the one consumers most affect through tire choice. It typically contains:

| Component | Typical % | Role |
| --- | --- | --- |
| **Natural rubber (NR)** | 14–30% | Elasticity, tear resistance; dominates winter tread compounds |
| **Synthetic rubber (SBR, BR, EPDM)** | 20–35% | Wet grip, abrasion resistance (SBR); low-temperature flexibility (BR) |
| **Carbon black** | 15–30% | Reinforcement, UV protection, electrical conductivity |
| **Silica (SiO₂)** | 0–25% | Wet grip + low rolling resistance simultaneously — the key innovation of modern tires |
| **Silane coupling agent** | 1–3% | Bonds silica particles to polymer chains (without it, silica does not reinforce effectively) |
| **Plasticisers / oils** | 5–15% | Reduce glass transition temperature, enable low-temperature flexibility |
| **Sulfur + accelerators** | 1–4% | Vulcanisation — cross-link polymer chains to set the final rubber structure |
| **Zinc oxide + stearic acid** | 1–5% | Vulcanisation activators |
| **Anti-ozonants / anti-oxidants** | 1–3% | Protect sidewall from UV and ozone cracking (appear as grey/brown surface bloom) |

## The glass transition temperature (Tg) — why compounds go stiff

Rubber is an amorphous polymer that transitions from an elastic, rubbery state to a rigid, glassy state as temperature falls below its glass transition temperature (Tg). Above Tg, the polymer chains can move freely, allowing the compound to conform to road surface texture and generate grip. Below Tg, movement is frozen — the compound becomes as rigid as hard plastic and loses traction.

For a summer compound with Tg of −10°C, driving at 0°C means the tread is approaching its glassy state — exactly why summer tires feel stiff and slide on cold mornings. For a winter compound with Tg of −50°C, temperatures down to −30°C still leave 20°C of headroom above the glass transition — the compound remains soft and grippy.

## Summer vs winter compound: key differences

| Property | Summer compound | Winter compound |
| --- | --- | --- |
| **Glass transition temperature (Tg)** | Higher (approx. 0°C to −30°C) | Lower (approx. −30°C to −60°C) |
| **Stiffness at 0°C** | Becomes stiff/glassy | Remains pliable and soft |
| **Wet grip at 5°C** | Reduced — compound too hard to deform into road texture | High — compound stays soft and conforms to surface |
| **Dry grip at 25°C** | Excellent — optimal operating temperature | Adequate — softer compound wears faster |
| **Rolling resistance in warm weather** | Low — compound at ideal consistency | Higher — softer compound deforms more |
| **Rubber type emphasis** | Higher SBR content, harder compound | Higher BR + NR content, more plasticisers |
| **Silica level** | High (wet + rolling resistance balance) | High (wet grip, lower temperature compounds) |
| **Wear rate at 30°C** | Normal | Faster (softer compound) |

## Silica vs carbon black: the revolution of the 1990s

Until the early 1990s, carbon black was the universal tire compound filler. Carbon black dramatically improved dry grip and abrasion resistance compared to unfilled rubber, but creating a tire that simultaneously had low rolling resistance and high wet grip seemed impossible — the two properties traded off against each other.

In 1992, Michelin and Continental independently developed silica-filled compounds using a silane coupling agent (TESPT). Silica generates hysteresis loss at higher frequencies (corresponding to wet grip) while generating less heat at lower frequencies (corresponding to rolling resistance). This discovery decoupled the wet grip / rolling resistance trade-off that had previously limited compound design.

| Property | Carbon black compound | Silica compound |
| --- | --- | --- |
| **Wet grip** | Good | Excellent — hysteresis at higher frequencies, better rubber-to-water interaction |
| **Rolling resistance** | Higher — more heat generated | Lower — energy loss reduced by ~20–30% |
| **Dry grip** | Excellent | Good (slightly lower than carbon black alone) |
| **Manufacturing complexity** | Simple — blends easily with polymer | Requires coupling agent (TESPT silane) to bond to polymer chain |
| **Heat build-up** | Higher | Lower |
| **Cost** | Lower | Higher |

## All-season compound: the compromise

All-season (M+S or 3PMSF) tires use compound formulations designed to remain above their glass transition temperature from about −15°C to +35°C. This is achieved by:

- Using higher natural rubber and butadiene rubber content than summer compounds
- Using more plasticisers than summer tires (but fewer than full winter tires)
- Targeting a Tg around −30°C to −45°C

The consequence is that the compound is softer than a summer tire at 25°C (meaning faster wear and slightly higher rolling resistance) and stiffer than a full winter tire at −10°C (meaning less grip on ice than a dedicated winter tire). See our [Seasonal tire guide](https://tirefitlab.com/learn/tire-seasons/) for a full seasonal comparison.

## Multi-compound tires

Many premium tires use different compound zones within the same tread pattern:

- **Centre rib compound** — harder, optimised for rolling resistance and wet straight-line braking.
- **Shoulder compound** — softer, optimised for dry cornering grip and lateral wet traction.

This is sometimes marketed as "dual compound" or "zone compound" technology. It allows manufacturers to score well on both the dry handling (shoulder) and fuel / wet straight-line (centre rib) dimensions of an independent tire test.

## More tools

- [Seasonal tire guide](https://tirefitlab.com/learn/tire-seasons/)
- [Winter driving tire guide](https://tirefitlab.com/learn/winter-driving/)
- [EU tyre label guide](https://tirefitlab.com/learn/eu-tyre-label/)
- [Tire tread depth guide](https://tirefitlab.com/learn/tread-depth/)
- [Tire size calculator](https://tirefitlab.com/tire-size-calculator/)
- [Tire & wheel reference guides](https://tirefitlab.com/learn/)

[Last reviewed: 2026-06-21](https://tirefitlab.com/methodology/)

Seasonal check

## Planning a long summer drive?

Use the budget and running-cost tools before a trip, especially if the current tires are worn or the replacement size changes diameter.

[Estimate tire budget](https://tirefitlab.com/tire-budget-calculator/)

## More in this topic: Ownership and maintenance

Pressure, age, wear, cost and service decisions after the tires are fitted.

- [**Tire age & DOT date code guide** How to find and decode the DOT date code on your tire sidewall to determine its manufacturing week and year, and when to replace old tires.](https://tirefitlab.com/learn/tire-age/)
- [**Tire pressure guide** What PSI should your tires be? How to find the correct pressure, what the TPMS light means, effects of over- and under-inflation, and how temperature changes pressure.](https://tirefitlab.com/learn/tire-pressure/)
- [**Cold tire pressure guide** How cold tire pressure works: the 1 PSI per 10°F (0.1 bar per 8°C) temperature rule, when to check pressure (cold only), morning vs driven-tyre readings, altitude effects, and seasonal adjustment.](https://tirefitlab.com/learn/cold-tyre-pressure/)
- [**Tire pressure for heavy loads and towing** When and how to increase tire pressure for heavy loads: XL (Extra Load) tire pressure requirements, laden vs unladen recommended pressure, adjusting rear axle pressure when towing, front vs rear axle pressure differences, and what happens when you tow on under-inflated tires.](https://tirefitlab.com/learn/tyre-pressure-load/)