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There are a few automotive calculators provided on these pages.  Feel free to check them out!

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Calculate Tire Diameter

Width (i.e. 245):

Height (i.e. 60):

Rim Diameter (in):

Tire Diameter (in) =

Tire Circumference (in) =


Speedo Driven Gear Teeth

Drive Gear Teeth:

Rear Gear Ratio:

Tire Height:

Driven Gear Teeth:

Formulas used on this pages:

  • MPH = (rpm * tire diameter) / (rear gear ratio * trans gear ratio * 336)
  • RPM = (rear gear ratio * (mph * 88)) / ((tire Circumference/12)) * trans gear ratio
  • KPH = MPH / 0.6215
  • Tire Height = (width / 25.4) * aspect Ratio / 100
  • Tire Diameter = (2 * tire height) + rim diameter
  • Tire Circumference = tire diameter * PI
  • Starting Line Ratio = first gear ratio * rear end gear ratio
  • Driven Gear teeth = (drive gear teeth * rear gear ratio * revs per mile)/1001
  • Revs per mile = 20168 / tire diameter

Other sites with valuable calculators:


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This website is a comprehensive collection of information regarding the installation of TREMEC transmissions into various vehicles. Material contained in here may be reproduced for PERSONAL USE ONLY. No material may be redistributed in electronic or printed form without the written permission of Brad Wedan (owner). Owner believes to the best of his knowledge this information to be correct, however no warranty is made as to its accuracy. Owner also disclaims any liability for financial loss, property damage or injury in connection with use of this information. Not affiliated with, endorsed or compensated by TTC, or any sanctioning body mentioned within. Any trademarked names are property of their respective trademark holder and are used for identification purposes only. Portions of this website may be copyrighted by other individuals or organizations.

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