Last revised: January 23, 2025

Metric pitch timing belts mate with same-pitch timing pulleys in power transmission systems where maintenance-of-speed ratio is an important design consideration. Metric pitch is the distance between belt teeth based on millimeters (mm).

With metric pitch timing belts, a timing pulley transmits force to the belt via evenly-spaced grooves that mate with the teeth in the belt. These same grooves and teeth prevent belt slippage.

Synchronous belt drives are highly-efficient devices. Synchronous belts come in a wide variety of materials and reinforcements. Metric pitch timing belts are also available in trapezoidal and curvilinear tooth form.

Specifications

Length, Width, and Number of Teeth — For a given pitch, a selected number of teeth will determine the belt length. Likewise, a specified belt length will determine the number of teeth for metric pitch timing belts.

Pitch is the most important consideration when searching for metric pitch timing belts. By definition, pitch is the distance from one tooth center to the adjacent tooth center.

Pitch choices for metric pitch timing belts include:

• T pitch, a metric trapezoidal pitch available in four pitch sizes: 2.5 mm, 5 mm, 10 mm, and 20 mm.
• AT pitch, a metric curvilinear pitch available in three pitch sizes: 5 mm, 10 mm and 20 mm.
• GT® pitch (Gates Rubber Company), a metric curvilinear pitch from that comes in three pitch sizes: 2 mm, 3 mm and 5 mm.
• HTD® pitch, or high torque drive pitch, is a metric curvilinear pitch developed by Uniroyal (now Gates Rubber Company). HTD pitch comes in five pitch sizes: 3 mm, 5 mm, 8 mm, 14 mm, and 20 mm.
• Super-torque, a metric curvilinear pitch available in six sizes from 2-mm pitch to 14-mm pitch.

Ultimate Tensile Strength (UTS) is the breaking strength or tension rating.

Maximum Operating Speed — Many products are rated for a maximum operating speed, dependent on material and timing belt geometry.

Types

Types of timing belts include double-sided, truly endless and open-ended.

Double-sided belts have teeth on both sides of belt.

Truly endless belts are manufactured as one closed loop; not spliced.

Open-ended belts come in a roll and may be cut and spliced to the desired length and number of teeth.

Materials

Materials of construction for metric pitch timing belts include:

• Neoprene
• Polyurethane
• Rubber
• Urethane

Material selection factors may include:

• Operating tension
• Environmental factors such as humidity and temperature
• Power transmission

Many metric pitch timing belts are reinforced with fibers or cables in the tension area of the belt. Reinforcement can significantly enhance the belt’s maximum operating tension. Metallic and non-metallic reinforcement fibers are available. Common materials for reinforcement also include:

• Fiberglass
• Kevlar (DuPont)
• Polyester
• Steel

Standards

BS ISO 5296 — Synchronous belt drives - belts with pitch codes MXL, XXL, XL, L, H, XH, and XXH — metric and inch dimensions

ISO 13050 — Curvilinear toothed synchronous belt drive systems

ISO 5295 — Synchronous belts — calculation of power rating

Timing Belts (Metric) FAQs

How do different materials used in timing belts affect their performance in various applications?

The materials used in timing belts significantly affect their performance in various applications. Here are some insights based on the information available:

Common Materials

Timing belts are typically made from rubberized polymers and may include synthetic or organic fibers for added strength. Fillers can also be used to enhance performance for specific applications.

Material Types and Their Effects

Neoprene, Polyurethane, Rubber, Urethane: These materials are commonly used for timing belts. The choice among them depends on factors such as operating tension, environmental conditions (humidity and temperature), and power transmission requirements.

Reinforcement Materials: Timing belts often incorporate reinforcement fibers or cables, which can be metallic or non-metallic. Common reinforcement materials include fiberglass, Kevlar® (DuPont), polyester, and steel. These reinforcements significantly enhance the belt's maximum operating tension.

Performance Factors

Operating Tension: The material and reinforcement used in a timing belt affect its ability to handle different levels of operating tension, which is crucial for maintaining performance under load.

Environmental Conditions: The choice of material can also influence the belt's performance in various environmental conditions, such as exposure to moisture or extreme temperatures.

Application-Specific Considerations

The selection of timing belt materials should be aligned with the specific requirements of the application, including the need for durability, flexibility, and resistance to environmental factors.

What are the advantages of using reinforced timing belts?

Reinforced timing belts offer several advantages that enhance their performance in various applications. Here are some key benefits based on the information available:

Increased Operating Tension

Reinforcement materials, such as fibers or cables, significantly enhance the belt's maximum operating tension. This allows the belt to handle higher loads and maintain performance under stress.

Material Options for Reinforcement

Reinforced timing belts can include a variety of materials such as fiberglass, Kevlar® (DuPont), polyester, and steel. These materials provide different levels of strength and flexibility, allowing for customization based on specific application needs.

Durability and Longevity

The use of reinforcement materials increases the durability of timing belts, making them more resistant to wear and tear. This can lead to longer service life and reduced maintenance requirements.

Environmental Resistance

Reinforced belts can be designed to withstand various environmental conditions, such as extreme temperatures and humidity, which can be critical for certain applications.

What are the differences between metallic and non-metallic reinforcement materials in timing belts?

The differences between metallic and non-metallic reinforcement materials in timing belts can significantly impact their performance and suitability for various applications.

Metallic Reinforcement Materials

Common Materials: Steel is a typical metallic reinforcement material used in timing belts.

Advantages

High Strength: Metallic reinforcements like steel provide high tensile strength, which can enhance the belt's ability to handle higher loads and maintain performance under stress.

Durability: Metallic materials are generally more durable and can withstand harsh operating conditions.

Considerations

Weight: Metallic reinforcements can add weight to the belt, which might not be ideal for applications requiring lightweight components.

Non-Metallic Reinforcement Materials

Common Materials: Fiberglass, Kevlar® (DuPont), and polyester are typical non-metallic reinforcement materials used in timing belts.

Advantages

Flexibility: Non-metallic materials like Kevlar® and polyester offer flexibility, which can be beneficial in applications requiring more adaptable belt movement.

Lightweight: Non-metallic reinforcements are generally lighter than metallic ones, making them suitable for applications where weight is a critical factor.

Corrosion Resistance: Non-metallic materials are typically resistant to corrosion, which can be advantageous in environments with moisture or chemicals.

Considerations

Strength: While non-metallic materials provide good strength, they may not match the tensile strength of metallic reinforcements in some applications.

These differences highlight the importance of selecting the appropriate reinforcement material based on the specific requirements of the application, such as load capacity, environmental conditions, and weight considerations.

How do environmental factors influence the choice of timing belt materials?

Environmental factors play a crucial role in the selection of timing belt materials, as they can significantly impact the performance and longevity of the belts. Here are some insights based on the information available:

Temperature and Humidity

Timing belts are often exposed to varying temperatures and humidity levels, which can affect their material properties. Materials like neoprene, polyurethane, rubber, and urethane are chosen based on their ability to withstand specific environmental conditions such as extreme temperatures and moisture.

Corrosion Resistance

In environments with high moisture or chemical exposure, non-metallic reinforcement materials such as fiberglass, Kevlar (DuPont), and polyester are preferred due to their corrosion resistance. This makes them suitable for applications where metallic reinforcements might degrade over time.

Load and Flexibility Requirements

Environmental conditions can also dictate the load and flexibility requirements of the timing belt. For instance, non-metallic materials offer more flexibility and are lighter, which can be beneficial in applications where weight is a critical factor and the environment demands adaptable belt movement.

Durability and Longevity

The choice of material can influence the belt's durability and longevity in specific environmental conditions. Reinforced timing belts, whether metallic or non-metallic, are designed to withstand harsh conditions, thereby extending their service life and reducing maintenance needs.

How do manufacturers test timing belts for environmental resistance?

Manufacturers test timing belts for environmental resistance through various standardized tests to ensure their performance and durability under different conditions.

Water and Oil Resistance Test

This test, known as the Water/Oil Spray Test, evaluates the timing belt's resistance to water and oil exposure. It is applicable to toothed belts of all lengths and helps determine how well the belt can withstand these environmental factors without degrading.

Cold Start Test

This test assesses the performance of toothed belts at low temperatures. It is crucial for applications where belts are expected to operate in cold environments, ensuring that they maintain flexibility and functionality.

Extension and Fabric Wear Test

This test measures the belt's ability to resist wear and tear over time, particularly focusing on the extension and wear of the fabric used in the belt. It helps in understanding the belt's durability under continuous use.

What are the common failure modes of timing belts in harsh environments?

Material Degradation

Exposure to extreme temperatures, humidity, or chemicals can lead to the degradation of the belt material, affecting its performance and lifespan. Non-metallic materials like Kevlar and polyester are often chosen for their corrosion resistance in such environments.

Wear and Tear

Continuous exposure to harsh conditions can accelerate wear and tear, particularly in the fabric and reinforcement materials of the belt. This can lead to reduced tensile strength and eventual failure.

Loss of Flexibility

In cold environments, timing belts may lose flexibility, which can lead to cracking or breaking. The Cold Start Test is used to assess the performance of belts at low temperatures to mitigate this risk.

Oil and Water Damage

Belts exposed to oil or water can suffer from material breakdown if not properly resistant. The Water and Oil Resistance Test evaluates how well a belt can withstand these conditions.

Timing Belts (Metric) Media Gallery

References

GlobalSpec—Timing Belts (Inch)

GlobalSpec—Fundamentals of timing pulleys and belts

GlobalSpec—Timing belt pulley design: What every product designer must know

Image credits:

SKF/North America | MISUMI USA