KEVOS® MAKEOS · Power Transmission
Synchronous (Timing) Belt Rating — MXL Torque and XL to XXH Power, Teeth in Mesh, Width
For an inch-pitch synchronous (timing) belt of MXL, XL, L, H, XH or XXH section, what torque or power does the widest standard belt carry on my small pulley at my speed, how much do too few teeth in mesh reduce it, and is the belt width I chose wide enough for the design power?
Ratings of synchronous belts by the ANSI/RMA IP-24 formulas the handbook gives: for MXL the torque rating Qr = d [2.63 − 3.21 × 10⁻³ d²] lbf·in for the 0.25 in belt (and the 0.12 and 0.19 in formulas), for XL, L, H, XH and XXH the power rating of the widest standard belt HP = d r [K1 − K2 (d r)²], with d the small pulley pitch diameter in inches from its teeth and pitch and r the faster shaft speed in thousands of rpm; the teeth in mesh factor (1.00 with six or more teeth, 0.20 less for each tooth below that), the belt width factor you read from the handbook table, the belt speed against the 6500 ft/min limit of the ratings, and the check against the design power.
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How this tool works
Inputs, units and where to find them
| Input | Unit | Typical source |
|---|---|---|
| Belt section (pitch) | choice | Synchronous belt section; the pitch is shown in brackets. |
| Teeth on the small pulley | teeth | Number of teeth (grooves) on the smaller pulley. |
| Speed of the faster shaft | rpm | Speed of the faster (smaller pulley) shaft. |
| Teeth in mesh on the small pulley | teeth | Number of belt teeth engaged with the small pulley. |
| MXL belt width | choice | Width of an MXL belt; the handbook gives a torque formula for each standard width. |
| Belt width factor (Table 48; 1.00 for the widest standard width) | Width factor read from the handbook table for the belt width you chose; 1.00 for the widest standard width of the section (0.38 in XL, 1.00 in L, 3.00 in H, 4.00 in XH, 5.00 in XXH). | |
| Duty | ||
| Power to transmit | kW | Power the drive must transmit. |
| Service factor | Service factor for the driver and driven machine. | |
What each input means
Open an input to see what it is, its units, the worked example and the common mistakes, with a small diagram.
What this means: Belt section (pitch)
- What it is
- Cross section of the synchronous belt to rate.
- Units and format
- Choose one of 6 options from the list: MXL (0.080 in); XL (0.200 in); L (0.375 in); H (0.500 in); XH (0.875 in); XXH (1.250 in).
- Example
- The form opens with “H (0.500 in)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the constants of the rating formula.
- Get it right
- The pitch of each section is shown in brackets.
What this means: Teeth on the small pulley
- What it is
- Number of teeth (grooves) on the smaller pulley.
- Units and format
- Enter a number in teeth: a whole number of teeth. The form accepts 8 teeth to 300 teeth. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 24 teeth as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Sets the pitch diameter and the rating.
- Get it right
- Count the grooves or read them from the pulley designation, e.g. 30L075.
What this means: Speed of the faster shaft
- What it is
- Speed of the faster shaft, the one with the smaller sheave.
- Units and format
- Enter a number in rpm: revolutions per minute. The form accepts 0.000001 rpm to 100000 rpm. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1450 rpm as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- The rating rises with speed until the belt speed limits it.
- Get it right
- Use the motor speed for a speed-reducing drive.
What this means: Teeth in mesh on the small pulley
- What it is
- Number of belt teeth engaged with the small pulley.
- Units and format
- Enter a number in teeth: a whole number of teeth. The form accepts 2 teeth to 200 teeth. Use a whole number. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 8 teeth as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Below six, each missing tooth lowers the rating by a fifth.
- Get it right
- From the drive layout; six or more give the full rating.
What this means: MXL belt width
- What it is
- Width of an MXL belt, which has its own torque formula for each width.
- Units and format
- Choose one of 3 options from the list: 0.25 in (6.4 mm); 0.19 in (4.8 mm); 0.12 in (3.0 mm).
- Example
- The form opens with “0.25 in (6.4 mm)” selected as a worked example. Choose the option that matches your case.
- Effect on the result
- Sets the MXL torque rating.
- Get it right
- Used only for the MXL section.
What this means: Belt width factor (Table 48; 1.00 for the wides…
- What it is
- Width factor for the belt width chosen, relative to the widest standard width.
- Units and format
- Enter a plain number with no unit. The form accepts 0.000001 to 1. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Multiplies the rating of the widest belt.
- Get it right
- Read it from the handbook width factor table; 1.00 for the widest standard width.
Duty
What this means: Power to transmit
- What it is
- Power the drive must transmit to the driven machine.
- Units and format
- Enter a number in kW: kilowatts. The form accepts 0.000001 kW to 100000 kW. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 5 kW as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Times the service factor, sets the design power.
- Get it right
- Use the motor rating or the measured power of the driven machine.
What this means: Service factor
- What it is
- Factor for the type of driver, driven machine and hours of running.
- Units and format
- Enter a plain number with no unit. The form accepts 1 to 5. Required: the tool does not calculate until every input is valid.
- Example
- The form opens with 1.4 as a worked example. It is an illustration, not a recommended value: replace it with your own figure.
- Effect on the result
- Raises the design power the belts must carry.
- Get it right
- Take it from the handbook service factor tables for the belt type.
Method and formulas
- d = teeth × pitch ÷ π (inches); r = rpm ÷ 1000.
- MXL: Qr = d [1.13 − 1.38 × 10⁻³ d²] (0.12 in), d [1.88 − 2.30 × 10⁻³ d²] (0.19 in), d [2.63 − 3.21 × 10⁻³ d²] (0.25 in) lbf·in; power = Qr × speed.
- XL (0.38 in) d r [0.0916 − 7.07 × 10⁻⁵ (d r)²]; L (1.00) [0.436 − 3.01 × 10⁻⁴ (d r)²]; H (3.00) [3.73 − 1.41 × 10⁻³ (d r)²]; XH (4.00) [7.21 − 4.68 × 10⁻³ (d r)²]; XXH (5.00) [11.4 − 7.81 × 10⁻³ (d r)²] hp.
- Kz = 1.00 for six or more teeth in mesh and 0.2 × (teeth − 1) below six (0.80 for five, down to 0.20 for two); corrected rating = rating × Kz; capacity = corrected rating × width factor; width factor needed = design power ÷ corrected rating.
- Example: the widest H belt carries 15.227 kW on the small pulley, so a width factor of 0.45972 is needed.
Limitations
- The ratings hold for pulley surface speeds up to 6500 ft/min (33 m/s).
- The belt width should not exceed the small pulley diameter, or side thrust becomes excessive.
- Ratings for a particular maker’s belts may differ; check the minimum pulley size for the speed.
- Example values are illustrations. Replace them with values for your actual task.
Typical uses
- Check that a timing belt is wide enough for a drive
- Find the torque an MXL belt carries on a small pulley
- Allow for drives with fewer than six teeth in mesh
Who it is for
- Machine designers
- Maintenance engineers
- Drive and conveyor designers
What you get
- Pitch diameter of the small pulley and belt speed
- Torque or power rating of the belt
- Teeth in mesh factor and corrected rating
- Width factor needed and the check against the design power
Interpreting the result
- With fewer than six teeth in mesh the rating falls by a fifth for each missing tooth.
- Double-sided belts have the same total rating as single-sided ones.
References
- Machinery’s Handbook, 29th edition (Industrial Press, 2012), printed pp. 2534–2536. Topic reference; no source tables or recommended settings are reproduced.
Learn the Concepts Behind This Tool
These KEVOS® Library readings explain the method this tool uses, with worked examples.
Useful alongside · Library collection
Belt or chain drive: selecting, installing and maintaining flexible power transmission
In Machine Elements and Mechanical Design
What it covers: Belt and chain drives are simple until they slip, stretch or wreck bearings. How to choose between them, size a drive properly, set tension and alignment, and maintain it for long life.
KEVOS® tools are screening and decision-support utilities. Verify important financial, engineering, safety, legal or operational decisions using appropriate professional standards and your organisation’s approved data.