PowerGrip® GT® Belt Drives

Useful Formulas and Calculations
Drive Design – continued
The number of teeth in mesh on the smaller
sprocket can be found as follows:
Teeth in Mesh =
(Arc) (n)
360
Where: Arc = Arc of contact; small sprocket, degrees
n = number of grooves, small sprocket
Drop any fractional part and use only the whole
number as any tooth not fully engaged cannot be
considered a working tooth.
If the teeth in mesh is less than 6, correct the belt
torque rating with the following multiplication
factors:
5 Teeth in Mesh – Multiply by 0.8
4 Teeth in Mesh – Multiply by 0.6
3 Teeth in Mesh – Multiply by 0.4
2 Teeth in Mesh – Suggest Redesign
1 Tooth in Mesh – Suggest Redesign
Torque loading due to flywheel effect (acceleration
or deceleration) can be calculated as follows:
Torque (pound size 7 - inches) =
0.039(RPM - rpm) (Wk 2 )
t
Where: RPM = Final revolutions per minute
rpm = Initial revolutions per minute
Wk2 = Flywheel effect, pound feet squared
(lb-ft 2 ) (1 ft-lb-sec 2 is equivalent to
32.2 lb-ft 2 )
t = time, seconds
Synchronous Belt
Tension
Effective Pull
T T - T S = 2(Q) = T e
pd
Where: T T = Tight side tension, pounds
T S = Slack side tension, pounds
Q = Torque Load, pound-inches
pd = Pitch diameter, inches
T e = Effective tension, pounds
Total Tension
T T + T S = 3(Q)
pd
Where: T T = Tight side tension, pounds
T S = Slack side tension, pounds
Q = Torque load, pound-inches
pd = Pitch diameter, inches
Tight Side Tension
T T = 2.5(Q)
pd
Where: T T = Tight side tension, pounds
Q = Torque load, pound-inches
pd = Pitch diameter, inches
Slack Side Tension
T S = 0.5(Q)
pd
Where: T S = Slack side tension, pounds
Q = Torque load, pound-inches
pd = Pitch diameter, inches
Centrifugal Belt Tension
T c = (K c ) (pd) 2 (rpm) 2
Where: T c = Centrifugal tension, pounds
K c = Belt mass constant
pd = Smaller pitch diameter, inches
rpm = Smaller sprocket revolutions per
minute
Working Tension
T w = (T e + T c) (SF)
Where: T w = Working tension, pounds
T e = Effective tension, pounds
T c = Centrifugal tension, pounds
SF = Service Factor
The flywheel effect of a sprocket can be estimated as
follows:
Wk 2 (lb-ft 2 ) = (F) (Z) (D4 - d 4 )
1467
Where: F = Face width of rim, inches
Z = Material density, pounds per cubic inch
D = Outside rim diameter, inches
d = Inside rim diameter, inches
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