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!
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
Select this if you have a:
T5 transmission that has been converted to a 6 tooth gear to correct the speedometer more accurately. The black 6 tooth internal drive gear was originally used in the 4-speed transmission, but it works great to exactly correct for 4.10s when used with a pink 19 tooth driven gear.
7 Tooth
Select this if you have a:
Factory 1983-1989 Mustang T5 or AOD
Ford Performance M-7003-Z World Class T5
Tremec 3550, TKO, TKO 500, TKO 600, TKX
Tremec T56 Magnum
1996-1998 Cobra T45
Normally, C4 transmissions use this 7-tooth application. LMR.com recommends checking your tooth count to be as accurate as possible.
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 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)
Due to factors beyond the control of LMR.com, we cannot guarantee against the improper use or unauthorized modifications of this information. LMR.com assumes no liability for property damage or injury incurred as a result of any of the information contained in this video. Use this information at your own risk. LMR.com recommends safe practices when working on vehicles and or with tools seen or implied in this video. Due to factors beyond the control of LMR.com, no information contained in this video shall create any expressed or implied warranty or guarantee of any particular result. Any injury, damage, or loss that may result from improper use of these tools, equipment, or from the information contained in this video is the sole responsibility of the user and not LMR.com.
Fetching speedo gear....
