Mustang Rear End Gear Ratios

When power comes from the engine, it needs some way to make it to the pavement. The system that transmits that power from engine to rear wheels is referred to as a drivetrain. The basics of your Mustang’s drivetrain are pretty straightforward. Power comes from your Mustang’s engine then travels to the transmission, which rotates the driveshaft. In order for the driveshaft’s rotation to travel to the rear wheels, your Mustang relies on a differential.

The input of the differential is a ring and pinion gear. It’s this gear that finally translates all of that power into motion. The ratio of that rear differential gear affects top speed, fuel efficiency, and acceleration.

Understanding your Mustang’s gear ratio can help you decide if you need to change it to fit your build goals or driving style.

What Is a Rear Gear Ratio?

Your driveshaft connects to the smaller pinion gear. This pinion gear then turns the larger ring gear using interlocking teeth. This is what turns the rear axle and with it, your Mustang’s rear wheels.

The number of times the driveshaft rotates for each rear wheel rotation is your Mustang’s rear gear ratio. This is also sometimes referred to as the final-drive ratio since it’s the last gear that must turn before power hits the pavement.

If you have a rear gear ratio of 3.31, the driveshaft rotates 3.31 times for each wheel rotation. (Transmission gear ratios also affect this, but those can be ignored for now).

Low vs High Gears

If you change your Mustang’s rear gear ratio to 4.10, then the driveshaft will rotate 4.10 times per each wheel rotation. You’ll see faster acceleration as your engine expends more energy for each wheel rotation. The downside of higher gears is that you’ll also sacrifice some top speed.

Because this makes the engine work harder, it can be bad for it long term. This is why people usually stay close to their Mustang’s stock rear ratio.

One good way to figure out how much you can increase your rear gear ratio is to look at other Mustangs from that generation. SVT Cobra Mustangs and Shelbys offer ideas for potential upgrades.

A lower gear ratio (2.73, 3.08, etc.) will have a slower acceleration. But lower rear gear ratios allow for higher top speeds and better fuel economy.

Higher gears are sometimes referred to as shorter gears and lower gears as taller. This literally refers to the size of the gear. Lower gears are physically taller than the higher ones. Some also refer to higher gears as “steeper.”

Key Takeaways

• Higher gear ratios, like 4.10 or 4.30, allow for quick acceleration but have a lower top speed.
• Lower gear ratios, like 2.73 or 3.31, get better fuel economy but have slower acceleration.
• Getting a gear that’s too high results in loss of traction and engine wear and tear.

Mustang Stock Rear Gear Ratios

Through the years, Mustangs have come with a wide range of rear gear ratios. Besides offering many optional gears, Mustangs also offered limited-slip differentials. This created many different potential option combinations. Because of this option abundance, early Mustangs have more rear gear ratios than modern Mustangs. The 1966 Mustang had 14 possible rear gear ratio/differential combinations. The entire S550 Mustang generation has had 4, due in part to the limited-slip differential option.

Even early Mustangs had limited-slip differentials as an option. In 1986, limited-slip differentials, or LSDs, became standard on all V8 Mustangs. By 2011, all Mustangs came with an LSD.

To find out which rear gear ratio your Mustang has, use the charts below. You can either look through all of the rear gear ratios by year, or if you already know your axle code, you can search specifically for that.

1965 | 1966 | 1967 | 1968 | 1969 | 1970 | 1971 | 1972 | 1973
1974-1978- Mustang II | 1979-1993- Fox Body | 1994-2004-SN95 | 2005-2014- S197 | 2015-2023 | 2024-Present

Which Rear Gear Is Best for Your Mustang?

Like with most Mustang modifications, there’s no simple “best” option. What’s best for your Mustang will depend on how it’s driven and what your build priorities are.

Street Car With Some Dragstrip Use

You’ll want a rear gear ratio that is good for straight-line acceleration but also can cruise on the highway. Most enthusiasts in this category find that a 3.73 gear ratio is right for them. If you also want to get relatively good fuel economy, a 3.55 is a good compromise.

Dragstrip Mustang

Road course Mustangs tend to have longer rear gear ratios, which means less time shifting.

For Mustangs built for drag racing, there are a lot of factors to consider. Your transmission, rear tires, and several other factors should be accounted for. For straight-line acceleration, it may be worthwhile to move to a higher gear, like a 4.10 or 4.30.

This will hurt your top speed and fuel economy. But if your Mustang’s destined for quarter-miles, those are less important than quick acceleration.

Road Use Only

For carving corners and cruising down highways, you’ll want a lower rear gear ratio. A 3.30 or 3.55 is perfect for your needs. With these rear gears, you won’t have to spend as much time shifting as you would with a 4.10 or 4.30. It will also be more comfortable at highway speeds.

Other Rear Gear Considerations

Your Mustang’s rear gear ratio is an important measurement that affects many other aspects of performance. Unfortunately, changing out your rear gear ratio isn’t as simple as swapping parts. All of the other parts that are dependent on rear gear ratio will also need to be reevaluated.

CJ's Gotta Have It Race At The Dragstrip

Speedometer Accuracy

Changing your Mustang’s rear gear ratio will also change your speedometer’s accuracy. This can have obvious legal ramifications. After replacing your rear gear, you’ll also need to recalibrate your speedometer.

Mustangs made before 1999 can get a new speedometer gear. Newer Mustangs will need to either use a tuner or get a Ford dealer to flash their ECU. Either method will be able to communicate with your Mustang’s internal computer.

Different Shift Points

Your shift points will change with a new rear gear ratio. For manual drivers, this just requires a period of adjustment. But for automatic drivers, you’ll need to follow the same process as for the speedometer swap out.

Change in Fuel Economy

Changing your rear gear ratio will either have a positive or negative effect on your mpg. Higher gears will reduce your mpg, lower gears will increase it. If your Mustang is your daily driver, this can be a big consideration.

It’s because of fuel efficiency that most Mustang owners select a middle-range gear. This offers good cruising mpg and sufficient power.

Mustang Rear End Gear Ratios

Your Mustang’s rear gear ratio is less obvious, but no less important, than transmission gear ratios and engine power. The process of changing out rear gears isn’t simple. Depending on your Mustang, you may have to change other parts as well.

But for many, it’s worth it to further custom tune their Mustang. Changing out the rear gear ratios can make your Mustang better at straight line acceleration or highway cruising. If you’re unsure, there are many other modifications you can make while you consider rear gear ratios.