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Everything You Need to Know About S550 Mustang Rear Gears

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Shop Mustang Rear Gears

Deciding what gear sizes to use is an important factor for maximizing your power or top speed. Check out our selection of rear gears to get the perfect ride.

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Your 2015+ Mustang’s engine redline and shift points are ultimately dictated by the rear gears in your build. This guide will go over what you need to know about S550 Mustang Gears.

What Are S550 Mustang Gears? 

Gears are part of the drivetrain and are located in the rear differential. Also called a ring and pinion setup, the gears on your S550 are helical and arranged with many thick teeth that interlock with each other. The gears impact how quickly your Mustang accelerates and at what point you have to shift at. While traditionally thought of as an intimidating subject, gears have a simple and straightforward function that can make or break your dream build.

Stock 2015+ Mustang Rear Gear Ratios

2015 Mustang came offered with the following rear gear ratios from the factory:

  • 3.31 – Mostly in automatic V6 Mustangs
  • 3.55 – Common for manual Mustangs
  • 3.73 – Standard for Performance Package Mustangs and the Shelby GT350/GT350R

These gearing ratios are fairly ideal for demographic. 3.31 gears are great for fuel economy and automatic Mustangs. 3.55 gears are a good in between gear, offering decent acceleration and overall drivability. 3.73 gears are the more performance oriented, making them perfect for the performance pack S550s as well as the track focused Shelby GT350.

3.73 Ring and Pinion Gear Set for 2015-2017 Mustangs
3.73 Ring and Pinion Set

Gear Ratios Explained

Gear ratios can be somewhat confusing at first glance due to their numbering and how they impact performance. The lower the number of the gear ratio, the longer or taller the gear is. This means the longer it takes to rev out your Mustang. Conversely, the higher the gear number, the shorter the gearing is. Tall gears are typically thought to be anything less than 3.31s, and short gears are thought to be anything higher than 3.73 with 3.55’s being the middle ground. 

When you go with a gearing as extreme as a 4.56, you will be redlining each gear fairly quickly, helping you to accelerate at an advanced rate. However, going the other way with that, having a 3.31 gear will take you a while to redline. Meaning you will be able to build up a decent bit of speed (MPH) in each gear.

S550 Gearing Setup for the Quarter Mile

With the MT-82 transmission, going with 3.73s is the general rule of thumb for S550 Mustangs. With most setups you will cross the quarter mile mark right at the top of 4th gear. However, there is a smaller subset of enthusiasts who argue going with 4.10s is better, even though it may require you to shift into 5th gear at the finish line. 

For automatics, most enthusiasts go with a 3.55 or 3.73 gear as it provides a more ideal shift point. As eluded to earlier, 3.73 gears tend to be the favored gear of choice for S550 Mustang builds.

S550 Mustang at the Drag Strip

S550 Mustang Gearing & Top Speeds

One thing to consider with re-gearing your Mustang is how it will impact your top speed. Going with a tall gear, like 3.31s, will afford you a high(er) top speed. Going with 3.73s or 4.10s will cut down on how fast your Mustang will go. Shorter gearing helps you to accelerate much quicker, providing you with a strong low and mid range power band, but ultimately cuts down on your top end.

Gearing for Boosted or Naturally Aspirated Builds

If you plan on going with a supercharger or turbocharger for your build, you will want to consider going with a tall gear, like a 3.31 or 3.55. Going with a tall gear allows you more time (or rather RPMs) to build up and get into boost. If you have a forced induction setup, your goal should be to remain in the boost for as long as you can, and a tall gear is a great way to do that. 

A naturally aspirated build is much more well suited for a shorter gear as it will drastically improve acceleration. 

2015-2017 GT Mustang with a 670HP Supercharger Kit

What are Gear Kits?

S550 Mustang gear kits give you everything you need to install a set of new rear gears. Typically, this includes:

  • The gears themselves
  • The proper fluids and oils
  • The seals
  • A tuner

A rear gear kit is the one-stop shop bundle for everything you need (minus the tools) to install a new set of rear gears properly on your Mustang. Be warned though, installing a set of gears is not something that should be taken on by an inexperienced wrencher as you need the proper know-how and tools to install a set of gear correctly. Installing a set of rear gears is best left to a shop or a professional.

Do I Need to Tune My Mustang if I Upgrade My Gears?

While your Mustang’s engine doesn’t necessarily need to be retuned or calibrated, your speedometer does. When you upgrade the gears on your Mustang, the speedometer will be off, not properly showing the accurate speed. A handheld tuner device can recalibrate your speedometer and display the accurate speed at which you are traveling. 

2015-2017 GT Mustang Hooked Up to a Tuner
Fitment includes: 2015, 2016, 2017, 2018, 2019, GT, V6, EcoBoost, ShelbyGT350