# Horsepower and Torque Rating Formulas

### TORQUE RATINGS

It is customary to use torque load requirements rather than horsepower load when designing drives using the small pitch MXL section belts. Torque ratings are shown in Table 18 for each standard belt width. Since these belts operate on small diameters resulting in relatively low belt speeds, torque is essentially constant for all rpms. These ratings are based on the adjacent formulas:

###### TEETH IN MESH FACTOR

The horsepower or torque ratings from Tables 18, 19, and 20 must be corrected for excessive tooth loading if there are less than 6 teeth in mesh between the belt and the pulley. Determine the proper factor Kz from the following Table 15 to correct for teeth in mesh.

###### NOMINAL TOOTH DIMENSIONS

Table 9 and Figure 7 show the nominal tooth dimensions for each of the standard belt sections. The tooth dimensions for double-sided belts are identical to those of a single-sided belt.

###### HORSEPOWER RATINGS

Horsepower ratings are used for belt sections MXL, XL and L. These ratings are for the widest standard belt*. To obtain the horsepower rating for other belt widths, multiply the horsepower rating by the appropriate factor shown in Table 16. The horsepower ratings (Tables 18, 19, and 20) are based on the following formulas: where:
Qr = The maximum torque rating (Ibf-inches) for a belt of specified width having six or more teeth in mesh and a pulley surface speed of 6500 feet/minute or less. Torque ratings for drives with less than six teeth in mesh must be corrected as shown in Table 15, Teeth in Mesh Factor.
d = Pitch diameter of smaller pulley, inches. The teeth in mesh may be calculated with the following formula:
Teeth in Mesh = [0.5 – (D-d/6C)]z1
where
D = pitch diameter, large pulley, inches
d = pitch diameter, small pulley, inches
C = center distance between shafts,inches
z1 = number of grooves in small pulley

*Total horsepower ratings for double-sided belts are the same as single-sided belts. Contact York Engineering for percent of horsepower available for each side of the belt.    