Gear Ratio/Speed Calculator

Select the button representing the field to calculate, then fill the other boxes.
Speed (MPH) RPM Tire Diameter Final Drive Ratio

Speed (MPH)
RPMs
Tire Diameter (Inches)   How can I calculate my Tire Diameter ?
:1 Final Drive Ratio (e.g. 3.08, 3.42, etc.)
Transmission Ratio Select a Transmission High-Gear Ratio

Before calculating, Check a Button at top for the value you want to solve for.

  (If you want to see more transmission gear ratios, see my transmission list)

NOTE: These calculations require JavaScript to be enabled in your browser!

Tire Diameter Calculator

Enter Tire Size Below

  - Example: A   P245/50ZR16   has a:

  • Tire Width of 245 mm
  • Aspect Ratio of 50 %
  • Wheel Diameter of 16 inches
  • And has a Z Speed Rating of 186+ MPH
Tire Width (mm)
Aspect Ratio
Wheel Diameter (Inches)

Tire Diameter (Inches)

SPEED RATINGS
Rating MPH
Q99
S112
T118
U124
H130
V149
W168
Y186
Z186+

For a wide variety of automotive calculations get the PSCalc software!

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