What Is a Belt Sheave?

A sheave is another name for a pulley used in a belt drive system. It transfers power from a driver shaft to a driven shaft using a belt.

There are always two main components:

• Driver sheave – connected to the motor
• Driven sheave – connected to the load

The size of these sheaves determines speed and torque changes.

If the driver is smaller than the driven, the output speed decreases.
If the driver is larger than the driven, the output speed increases.

What Does a Belt Sheave Speed Calculator Do?

A belt sheave speed calculator performs four main functions:

1. Speed Calculation
2. Power Calculation
3. Geometry Analysis
4. System Comparison

Instead of solving multiple formulas manually, you enter your inputs once and get a full analysis instantly.

1. Speed Calculation

Speed is the most common reason people use this calculator.

Core Formula

The driven speed is calculated using:

Speed Ratio

If the ratio is:

• Greater than 1 → Driven rotates slower
• Less than 1 → Driven rotates faster

Belt Speed

Belt speed is also calculated in:

• Feet per minute (ft/min)
• Feet per second (ft/s)

High belt speeds can cause:

• Excess wear
• Heat buildup
• Reduced belt life

Most standard V-belts operate safely below 5000 ft/min.

2. Power and Torque Calculation

Power and torque are directly related.

Power from Torque

Torque from Power

The calculator automatically determines:

• Input power
• Input torque
• Transmitted power
• Design power
• Required torque

Belt Efficiency

Each belt type has a different efficiency rating.

Typical efficiency values:

• Classical V-belt → 94%
• Narrow V-belt → 93%
• Wedge V-belt → 92%
• Timing belt → 98%
• Flat belt → 96%
• Poly-V belt → 95%

Higher efficiency means less power loss.

3. Service Factor and Design Power

The service factor accounts for real-world conditions such as:

• Shock loads
• Long operating hours
• Harsh environments
• Heavy startup loads

Design power is calculated as:

Typical service factors:

• Light duty → 1.0
• Normal duty → 1.25
• Heavy duty → 1.5
• Extra heavy → 1.75
• Severe duty → 2.0

If you undersize your belt by ignoring service factor, failure is likely.

4. Geometry Analysis

Geometry affects belt life and grip.

The calculator determines:

• Open belt length
• Crossed belt length
• Wrap angle
• Contact angle
• Center distance

Why Wrap Angle Matters

A higher wrap angle means better grip.

Low wrap angle can cause:

• Slippage
• Reduced power transmission
• Increased belt wear

If the center distance is too short, tension increases and bearing life decreases.

How to Use the Belt Sheave Speed Calculator

Here is a simple step-by-step process:

Step 1: Enter Driver Sheave Diameter

Example: 6 inches

Step 2: Enter Driven Sheave Diameter

Example: 10 inches

Step 3: Enter Driver Speed

Example: 1750 RPM

Step 4: Enter Power or Torque

Optional but recommended for full analysis

Step 5: Select Belt Type

Choose based on your system

Step 6: Select Service Factor

Match real operating conditions

Step 7: Enter Center Distance

Step 8: Choose Calculation Type

• Speed
• Power
• Geometry
• Comparison

Click Calculate Speed to see complete results.

Example Calculation

Let’s use:

• Driver Diameter = 6 inches
• Driven Diameter = 10 inches
• Driver Speed = 1750 RPM

Driven Speed

The driven sheave runs slower than the driver.

If input power is 5 HP and belt efficiency is 92%:

Transmitted power = 4.6 HP

With service factor 1.5:

Design power = 6.9 HP

This ensures the system can handle heavy loads safely.

Common Mistakes to Avoid

1. Ignoring service factor
2. Using wrong belt efficiency
3. Setting center distance too short
4. Running excessive belt speed
5. Confusing diameter ratio direction

Even small input errors can change results significantly.

When Should You Use a Belt Sheave Speed Calculator?

Use it when:

• Designing a new belt drive system
• Changing pulley sizes
• Replacing a motor
• Increasing output speed
• Checking load capacity
• Troubleshooting belt slippage

It is useful in:

• Industrial machinery
• HVAC systems
• Automotive performance setups
• Workshop equipment
• Agricultural machines

Why This Calculator Is Valuable

Manually calculating:

• Speed
• Torque
• Power
• Belt length
• Wrap angle

can take time and increase risk of mistakes.

This calculator provides:

• Instant results
• Efficiency correction
• Service factor adjustment
• Geometry validation
• System comparison

It gives both engineering accuracy and practical guidance.