Gear efficiency: involute spur (best), worm (worst). All other geometries
fall in between those values. The bevel gear is as good as the spur but the
SPIRAL bevel gear falls off in efficiency due to wiping or sliding action.
The hypoid also suffers the sliding action but since the pinion centerline
is not concentric to the ring gear centerline, the efficiency is worse than
the spiral bevel gear. "Spiral" anything is used for strength, smooth load
transfer, or quiet operation, all due to more than one tooth in engagement
but all are less efficient than a spur gear.
From: "23weldon" <firstname.lastname@example.org>
( Edit . . . ) Correct me if I'm wrong; but isn't the spiral bevel type a
derivation of the involute spur gear which theoretically has no sliding
contact, only rolling? If so then perhaps the only sliding that goes on is
due to the inevitable manufacturing inaccuracies that come with a very
complex geometry between mating parts?