This formula is for general conditions and normal belt application. Factor K1 defines the influence of rubber kality.For example.
Cover thiknes,mm K1
< 3 1
< 5 1.3
< 8 1.6
Tensil strength,Mpa K1
15-18 0.85
18-22 1
22-26 1.3
For heat resistance belt
Temp. 60oC 125 oC 160 oC
1 0.55 0.2