First Gear

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Fig 1: Identifying First Gear Planetary Operation

Courtesy of MAZDA MOTORS CORP.

FIRST GEAR ROTATION SPEED REFERENCE

Planetary gear	Rear
Internal gear	0 (fix)
Planetary carrier	N_C (output)
Sun gear	N_S (input)

Suppose the gear ratio in first gear is i₁ ,

Fig 2: Identifying 1st Gear Ratio Formula (1 Of 2)
Courtesy of MAZDA MOTORS CORP.
From the result N_R =0 in formula (1), the relation between the gear ratio in first gear and the rotation speed of the planetary gear set is indicated in the formula below.
(Z_RR +Z_SR ) N_C =Z_SR N_S
Therefore,

Fig 3: Identifying 1st Gear Ratio Formula (2 Of 2)
Courtesy of MAZDA MOTORS CORP.
As a result, the gear ratio in first gear is 2.785.