How to Use the Elongation Method for Accurate V-Belt Tensioning
Elongation method: measure free length, apply factor, tension precisely—banish guesswork, protect bearings, extend belt life on heavy drives.
What Is the Elongation Method of Belt Tensioning?
The elongation method calculates the correct belt tension by measuring the belt’s free length (no tension applied) and then applying a calculated elongation factor to determine the proper tensioned length. This ensures the belt is tightened to an exact specification, rather than relying on guesswork or “feel.”
When to Use This Method
- Ideal for large belt drives
- Recommended for belts where accurate tensioning is critical
- Must be used with extra care for Kevlar cord belts (such as BESTORQ Thunder)
Step-by-Step Elongation Method Process
1. Find the Elongation Factor
Consult the elongation factor chart for your belt cross-section, type, and smallest pulley diameter.
2. Measure the Free Length
With no tension applied, wrap a non-stretch steel tape around the belt to measure its outside length.
Tip: Never use string—it will stretch and give inaccurate results.
3. Calculate the Tensioned Length
Multiply the free length by the elongation factor to get the tensioned length.
4. Install and Tension the Belt
Mount the belt, then tighten until its measured outside length equals the calculated tensioned length.
Example
For an 8V2000 banded belt on a drive with a 20-inch driver pulley:
- Free Length: 200.375 inches
- Elongation Factor: 1.0132 (from chart)
- Tensioned Length: 200.375 × 1.0132 = 203.02 inches
Tighten until the belt measures 203 inches in place.
Elongation Factors for Common Belt Types
BESTORQ provides elongation factor charts for:
- 3VX & 3V – Single and banded
- 5V & 5VX – Single and banded
- 8V – Single and banded
- D Section
- A & AX Section
- B & BX Section
- C & CX Section
Each factor varies for new vs. used belts and depends on the smallest pulley diameter in the system.
Benefits of the Elongation Method
- Accuracy: Sets belt tension to exact specifications
- Consistency: Works across multiple drives and belt types
- Extended Belt Life: Prevents under- or over-tensioning
- Bearing Protection: Reduces risk of premature bearing wear
