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Mustang Speedometer Gear Calculator

Created by Taylor Ward
Last Updated 3/25/2021

Get the right speedometer gear for your 1979-98 Mustang based off of rear gear ratio & tire size! No guessing with this Mustang Speedometer Gear Calculator!

Viewing this install and using the information shared is subject to the terms set forth here - View the LMR Install Instructions Disclaimer.

FOLLOW: mustang , 79 93 mustang , 94 04 mustang , fox body , sn95 , video , installation , 5.0resto , driveline , speedometer

Mustang Speedometer Gear Calculator

 * see step 2 below

How to use the Mustang Speedometer Gear Calculator

Step 1 - Select Transmission Type

This is pretty straightforward, select "Manual" for a manual transmission or "Automatic" for an automatic transmission.

Step 2 - Select Speedometer Drive Gear Teeth

  • 6 Tooth
    • T5 transmissions may be converted to 6 tooth gear to correct speedometer more accurately. The black 6 tooth internal drive gear was originally used in the 4 speed tranny, but works great to exactly correct for 4.10s when used with a pink 19 tooth driven gear.
    • 83-89 T5 has a yellow 7 tooth internal drive gear
    • 90-95 T5 has a greenish/yellow 8 tooth internal drive gear
    • FRPP M-7003-Z T5 has a yellow 7 tooth internal drive gear
  • 7 Tooth
    • Select this if you have a:
      • factory 1983-1989 Mustang T5 or AOD
      • Ford Racing M-7003-Z World Class T5
      • Tremec 3550, TKO, TKO 500, TKO 600, TKX
      • Tremec T56 Magnum
      • 1996-1998 Cobra T45
    • Or you are converting your 1990-1995 Mustang T5 to a 7 tooth drive gear
  • 8 Tooth
    • Select this if you have a:
      • factory 1990-1995 Mustang T5, AOD, AODE
      • 1996-1998 GT T45, AODE, 4R70W
      • 1994-1998 V6 T5, AODE, 4R70W

Step 3 - Select Rear End Axle Gear Ratio

Mustang rear gears from 2.73:1 all the way to 4.56:1, pick the ratio you currently have or are planning to install.

Step 4 - Select Tire Width

Your tire width is measured in mm. For example, if your tire size is 275/40/17, your tire width would be 275.

Step 5 - Select Tire Series

Your tire series, or aspect ratio, is measured in a percentage based on tire width. For example, if your tire size is 275/40/17, your tire series (aspect ratio) would be 40. This means your tire sidewall is 40% as tall as the tread is wide.

Step 6 - Select Rim Diameter

Your rim diameter is measured in inches. For example, if your tire size is 275/40/17, your rim diameter would be 17.

Step 7 - Click "Calculate Speedo Gear" Button

The Mustang Speedometer Gear that most closely matches your inputs will display on the right of the screen next to the calculator!

A Few Considerations

  • You cannot change the output shaft mounted drive gear in an Automatic Transmission as the gear is part of the output shaft.
  • Do not use a 23 tooth speedometer driven gear on a 1996-1998 Mustang GT or Cobra T45, AODE, or 4R70W. It will self destruct in a matter of feet.
  • The only way to correct the speedometer on a 1999-2010 Mustang is via a Speed-Cal, or an aftermarket Tuner (Such as SCT)
  • The only way to correct the speedometer on a 2011 and newer Mustang is via an aftermarket Tuner (Such as SCT)

About the Video

Mustang Speedometer Gear Calculator from LMR.com

Check out our YouTube channel for even more tech tips, installation videos, how-tos, and more. The best place to go for anything Mustang related!

Published on 2013-08-06
Tired of getting a different answer everytime you ask what speedometer gear you need in your Stang? Well we have created the ultimate solution to this problem - The LatemodelRestoration.com Mustang Speedometer Gear Calculator! All you have to do is plug in your transmission, rear end gears and tire size information to get the most accurate part for your Stang! This is the perfect speedometer gear tutorial for your SN-95 and Fox Body Mustang and best of all you don't even have to remember the calculation formula. Read the article in the link above for speedometer correction for all 79-2014 Mustangs.

Be sure to bookmark this calculator and share it with your friends! This calculator will work for your manual transmissions such as Tremec t5, t45, TKO 500/600 and more. Plus it will calculate for automatic transmissions such as AODE, 4R70W and more!

We carry a wide selection of Mustang speed correction parts, We also have gear kits available to save you time and money.

17,18,19,20,21,23 tooth Speed-o-meter Gears available
6,7 tooth Drive Gears available
0:00:00 - 0:00:13
If you are changing out the rear gears on your fox body or SN95 Mustang, you are going to have to correct your speedometer. The most popular method for doing so is by swapping out the driven gear on the end of the speedometer cable or speed sensor.

0:00:13 - 0:00:40
To figure out which gear you need, visit LatemodelRestoration.com and use our exclusive Mustang speedometer gear calculator. You can select your transmission, manual or automatic, your drive gear teeth, 6,7 or 8, pick out which gear ratio you're using and then select your tire size. Click the calculate now button and we'll tell you exactly what you need to correct your speedometer.

0:00:40 - 0:00:59
Regardless of the gear ratio you choose we offer speedometer driven gears in many different tooth counts for both manual and automatic transmissions as well as the internal drive gear for t5 transmissions. These internal drive gears are pretty difficult to swap out requiring you to remove the tail shaft review transmission.

0:00:59 - 0:01:17
Swapping out the speedometer driven gears extremely simple are you going to do is remove the single retaining bolt, slide the cable or sensor out in the transmission, remove the clip, slide your old gear off, put your new gear on, reinstall the clip, slide it back in the transmission and reinstall the retaining bolt.

0:01:17 - 0:01:21
Check out the speedometer gear and the speed correction category on LatemodelRestoration.com and get your speedometer back on the straight and narrow today!

Mustang Speedometer Gear Calculator Tech Info