Theory of Machine
The maximum efficiency of spiral gears is (where θ = Shaft angle, and φ = Friction angle)

cos (θ + φ) + 1/ cos (θ - φ) + 1
sin (θ + φ) + 1/ cos (θ - φ) + 1
cos (θ - φ) + 1/ sin (θ + φ) + 1
cos (θ - φ) + 1/ cos (θ + φ) + 1

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Theory of Machine
The Ackerman steering gear mechanism is preferred to the Davis steering gear mechanism, because

The Ackerman steering gear consists of turning pairs
Both (A) and (B)
The Ackerman steering gear is most economical
Whole of the mechanism in the Ackerman steering gear is on the back of the front wheels

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