Gear Ratios for Miatas

Using the gear ratios provided in the Miata Drivetrain Interchange Guide 
the total gear ratio from engine to axle is:

94-97 5-speed   12.86:1 7.74:1 5.45:1  4.10:1  3.34:1
99+ 5-speed    13.5:1 8.12:1 5.72:1 4.30:1 3.50:1
6-speed*     14.7:1 8.87:1 6.43:1 4.91:1 3.91:1 3.30:1
Mazdaspeed 15.4:1 9.30:1 6.75:1 5.15:1 4.10:1 3.46:1

The 90-93 have the same gear ratios as the 99+ 5-speed.
* 6-speed with 3.909 final drive -- that was changed to 4.1 sometime after 2001

Revolutions per mile:
185/60-14 Yokohama ES100, 914
195/50-15 Yokohama ES100, 914
205/45-16 Yokohama ES100, 891
205/40-17 Yokohama ES100, 884
205/50-16 Yokohama ES100, 861
205/45-17 Yokohama ES100, 854

Top speed in each gear (7000 RPM rev limiter for 1.8L, 7500 for 1.6L)
Formula: (Rev limit * 60 min/hour) / (Gear ratio * revolutions per mile)

90-93       37 61 86  115  141  (3200RPM @ 60MPH)
94-97       36 59 84  112  137  (3050RPM @ 60MPH)
99+ 14",15" 34 57 80  107  131  (3200RPM @ 60MPH)
99+ 16"     35 58 82  110  135  (3090RPM @ 60MPH)
6-speed 15" 31 52 71 94 118 139 (3010RPM @ 60MPH)
6-speed 16" 32 53 73 96 121 143 (2940RPM @ 60MPH)
Mazdaspeed  29 47 65 86 108 128 (3060RPM @ 60MPH)
5-speed '06 38 63 90  120  147  (2873RPM @ 60MPH)
6-speed '06 31 53 73 102 120 144 (2937RPM @ 60MPH)