Watch Your Pre-Tension: EPDM Timing Belts Behave Differently

We provide further insights into the latest generation of CONTI SYNCHROFORCE timing belts. It directly follows up on our article: ContiTech Timing Belts: the New EPDM Generation Is Coming, where we introduced the change and explained in more detail what it means in practice and the benefits it brings.

Now we take a practical look at these new belts, which have replaced their predecessors in the ContiTech product range since January 2026 – focusing on what should not be overlooked when transitioning to the new belts.

• The New Generation of ContiTech Timing Belts in Practice
• Example Application
• Proper Belt Pre-Tension

The New Generation of ContiTech Timing Belts in Practice

They have exactly the same dimensions – pitch, length, and profile – as their chloroprene (CR) predecessors, making them easy to replace on existing drives. However, they are not identical, and it is essential to verify the correct pre-tension frequency after installation.

Thanks to the advanced EPDM compound used for the belt body, the new CONTI SYNCHROFORCE belts offer significantly higher temperature resistance, increased power transmission, and longer service life. But the change in material also results in different dynamic characteristics.

EPDM belts have a slightly lower mass. According to the equation for the natural frequency of a free belt span, the frequency is inversely proportional to the square root of the belt mass. As a result, lighter EPDM belts vibrate at higher frequencies under otherwise identical drive conditions – the correct pre-tension therefore corresponds to higher frequency values than with previous CR belts.

To illustrate this, we have prepared a model calculation example showing the extent of the difference. You can find it below in the next section of this article. The difference in correct settings can reach up to approximately 12%.

The exact value of the correct frequency can only be determined by a calculation using the CONTI PROFESSIONAL online application. If needed, we will be happy to assist you.

Drive Calculation and Optimization by TYMA CZ

Example Application:
CONTI SYNCHROFORCE CXP → CONTI SYNCHROFORCE ADVANCE

The importance of accounting for different belt characteristics during setup can be demonstrated with a specific example. Consider a typical application – a compressor drive with a 3:1 speed ratio (step-up).

Until now, the drive has used a chloroprene belt with a polyamide fabric cover and glass fiber tension members: HTD 8M-1280-20 CONTI SYNCHROFORCE CXP (8 mm pitch, 1280 mm length, 20 mm width). This is now being replaced with a next-generation EPDM belt: HTD H8M-1280-20 CONTI SYNCHROFORCE ADVANCE.

From a geometric perspective, the belts are fully interchangeable. However, the material difference affects how the belt behaves under tension.

CONTI SYNCHROFORCE: Calculated Values for the Original CR Belt and the New EPDM Belt Under Identical Drive Conditions

Parameter	CXP (CR)	ADVANCE (EPDM)
Service factor C0err	1.90	2.17
Overall system power rating	28.57 kW	32.49 kW
Peripheral force Fu	833 N	833 N
Static strand tension Fstat	617 N	634 N
Belt mass	0.114 kg/m	0.096 kg/m
Reference frequency fstat	96 Hz	106 Hz

The load on the drive remains the same, as does the peripheral force. However, the new belt introduces two key differences:

• Higher power reserve and drive safety: approx. +14%
• Higher reference frequency: approx. +10 Hz

When replacing the belt, the required pre-tension force (static span force) does not fundamentally change. What changes is the frequency value used for setting the belt.

Applying the same reference frequency as for the original belt would result in under-tensioning, increasing the risk of tooth jumping, belt damage, or premature failure.

Alternative Scenario: Using CONTI SYNCHROBELT

If the same compressor were equipped with a lower-performance CONTI SYNCHROBELT, a wider belt would be required (H8M-1280-50). The system would require larger pulleys, resulting in increased weight and installation space. This belt would then be replaced with the new EPDM-based CONTI SYNCHROFORCE.

Even in this scenario, the reference frequency would need to be adjusted from f_stat = 55 Hz to 60 Hz – again by approximately 10%.

CONTI SYNCHROFORCE Belts in the TYMA CZ Online Store

Proper Belt Pre-Tension = Half the Battle for a Healthy Drive

If a timing belt is not sufficiently tensioned, tooth jumping may occur during engagement with the pulley, potentially leading to immediate damage or belt failure. This risk can be eliminated by maintaining the correct pre-tension – through proper initial setup and regular inspection of the drive.

The required tension force depends on the drive configuration, operating parameters, load characteristics, and the magnitude of shocks or acceleration. In OEM machines, the correct frequency values for setting and checking the pre-tension of a specific belt are clearly defined by the manufacturer in assembly instructions, user manuals, or service guidelines. When replacing the specified belt with a different type, these values must be recalculated.

Preventive Inspection

For approximate checks, the vibration frequency can also be measured acoustically using the Make Power Smart mobile application from ContiTech. However, for the latest generation of EPDM-based CONTI SYNCHROFORCE timing belts, not all belt types may yet be available in the application.

Belt Tension Gauges in the TYMA CZ Online Store