What is stronger a spiral bevel gear or a straight cut bevel gear?

If both gears designed and manufactured correctly, spiralbevel gear is stronger compare to a straight bevel gear. Spiral bevel gear is also quieter. For example, in mineral processing industry, spiral bevel gears are used in rock crashers because of the higher endurance. When the tooth is spiral (helical) it becomes possible to increase the size of the gear tooth without reduction of the contact ratio. The larger tooth is stronger compare to a smaller tooth. The reason why straight bevel gears are still used is because spiral bevel gears are more expensive in design and manufacturing, thanks to use of expensive spiralbevel gear cutting machines from Gleason Works or from Klingelnberg AG. In 1990, it became possible to manufacture spiral bevel gears on universal CNC milling machines, because of the development of special spiralbevel software for 3d CAD gear tooth modeling. Today, thanks to spiralbevel software, both straight and spiral bevel gears are manufactured on CNC milling machines at the same low cost.