What gear ratios are available for a Ford 8 inch rear end?

The Ford 8-inch rear end offers a wide range of gear ratios, from roughly 2.75:1 to about 4.89:1 in stock and common aftermarket configurations, with additional options available through specialty builds. The exact ratios depend on model year, vehicle line, and whether you’re looking at factory specs or aftermarket gear sets.

Overview of available gear ratios

The Ford 8-inch axle has been produced for many decades across various car and light-truck lines, and gearing varied by year, model, and market. The following list captures the spectrum you’re likely to encounter when selecting, restoring, or upgrading an 8-inch axle.

• 2.75:1


• 3.00:1


• 3.25:1


• 3.50:1


• 3.73:1


• 4.10:1


• 4.30:1


• 4.56:1


• 4.89:1


• 5.13–5.38:1 (rare and typically tied to specialized builds or aftermarket offerings)

Note: Availability varies by year, model, and source. Modern restorations and builds often rely on aftermarket gear sets to hit non-stock ratios, so verify the exact gearing when planning a project.

How to identify your current ratio

Knowing the precise ratio is essential for maintenance planning, gearing a build, or diagnosing performance. Use one of the following methods to confirm your 8-inch axle’s gear ratio.

1. Check the axle tag or stamping: Many Ford 8-inch rears carry a tag or stamping that lists the ring gear or axle ratio. Look for a code such as “R9” or a direct ratio like “3.00” on the tag near the differential cover or on a tag mounted to the housing.


2. Count teeth on the ring gear and the pinion: If the tag isn’t legible or present, remove the differential cover and count the teeth on the ring gear and on the pinion gear. The ratio is determined by dividing the number of ring teeth by the number of pinion teeth (e.g., 45 ring teeth / 15 pinion teeth = 3.00).


3. Verify with source documents or a professional: If you’re restoring a classic or buying a used unit, the build sheet, window sticker, or a trusted VIN/axle database can confirm the ratio. When in doubt, consult a drivetrain specialist or the supplier.

Bottom line: Accurate identification ensures you select compatible gears and avoid incompatible parts in a build or upgrade.

OEM options vs aftermarket options

Factory-installed ratios on the 8-inch range from efficient highway gears to lower numerical gears for performance or heavy-load duties. Aftermarket gear sets greatly expand the options, enabling tall gears for cruising or short gears for sprinting, depending on your goals.

OEM-era options

In factory catalogs and production cars, the 8-inch offered a spectrum that included several mid-range gears, with some models using shorter or taller gears depending on the drivetrain, market, and year. The commonly observed ratios among stock configurations included 2.75, 3.00, 3.25, 3.50, and 3.73, with higher or lower options appearing in trucks or specialty models.

• 2.75:1


• 3.00:1


• 3.25:1


• 3.50:1


• 3.73:1


• 4.10:1


• 4.30:1


• 4.56:1

Not every ratio appeared in every model year; availability depended on the specific vehicle line and production run.

Aftermarket options

Aftermarket gear suppliers offer new gear sets and complete rear assemblies for the Ford 8-inch, broadening the range far beyond stock catalogs. This enables configurations suitable for drag racers, highway cruisers, or stubborn off-road builds.

• 2.75:1


• 3.00:1


• 3.25:1


• 3.50:1


• 3.73:1


• 4.10:1


• 4.30:1


• 4.56:1


• 4.89:1


• 5.14:1


• 5.38:1

When using aftermarket gear sets, verify compatibility with your axle width, pinion size, and any limited-slip or carrier requirements. Aftermarket options also help tailor RPM and acceleration characteristics to your intended use.

Considerations when choosing a ratio

Choosing the right gear ratio for a Ford 8-inch involves balancing performance, efficiency, and reliability. The following considerations help guide the decision:

• Engine torque and horsepower: A strong, torquey engine benefits from taller gears to reduce engine speed at cruising, while a high-revving or power-adapted setup may favor shorter gears for quicker acceleration.


• Tire size and final drive: Larger tires effectively raise the overall gearing; changes in tire diameter require compensating the ratio to maintain desired engine RPM at highway speeds.


• Transmission compatibility: The chosen axle ratio should align with your transmission’s torque band and the intended driving role (daily driving, performance, or racing).


• Vehicle weight and use-case: Heavier vehicles or those used for towing typically prefer lower numerical gears; lighter builds can tolerate taller gear ratios for better fuel economy and highway comfort.


• Component strength and durability: Higher numerical gears increase pinion and ring gear load; ensure all drivetrain components are rated for the expected power and torque.

Bottom line: There isn’t a universal best ratio. Your goal, power level, tire size, and usage pattern determine the optimal gearing—and the exact parts you’ll need.

Summary

The Ford 8-inch rear end supports a broad spectrum of gear ratios, from efficient highway gears to aggressive performance configurations. OEM offerings varied by year and model, while aftermarket gear sets extend the range even further. When selecting a ratio, consider engine torque, tire diameter, transmission pairing, and intended use, and verify the ratio on your axle with the tag or tooth-count method described above. Consulting reputable retailers or drivetrain specialists helps ensure you choose a gearing solution that’s durable and well-matched to the rest of your build.

How do you tell if you have 3.73 or 4.10 gears?

You can tell if you have 3.73 or 4.10 gears by manually counting, checking the differential cover for a tag, or finding the ratio stamped on the ring gear. The most direct method is to lift the rear wheels, rotate one tire one full revolution, and count how many times the driveshaft turns; 3.75 turns indicates 3.73 gears, while slightly over 4 turns indicates 4.10 gears.
 
This video demonstrates how to check your gear ratio by counting the driveshaft turns: 48sBent Motorsports OffroadYouTube · Sep 22, 2023
Method 1: Manual count (with the vehicle jacked up)

1. Jack up the vehicle: Safely lift the rear of your vehicle and secure it on jack stands. Ensure the wheels are off the ground. 
2. Mark the driveshaft and a tire: Place a mark on one of the rear tires and a corresponding mark on the driveshaft. 
3. Rotate the tire: Rotate the marked tire forward one full revolution. For an open differential, you may need to lift only one wheel and have someone hold the other stationary, or lift both wheels and rotate one tire twice while the other tire is on the ground. For a locked differential, lift both rear wheels and have one tire rotate once while the other rotates once in the opposite direction. 
4. Count the driveshaft turns: Count how many times the mark on the driveshaft has rotated. 
   • 3.73 gears: The driveshaft will turn approximately 3.753.753.75 times for one full tire revolution. 
   • 4.10 gears: The driveshaft will turn a little over 444 times for one full tire revolution. 

Method 2: Check the differential cover tag 

1. Locate the tag: Look for a small metal tag that is usually bolted to the differential cover. It may be on one of the bolts. 
2. Read the ratio: If the tag is still present, the gear ratio will be stamped on it. It will likely be a number like "3.73" or "4.10". 

You can watch this video to learn how to find the differential cover tag: 51sFlawed OffroadYouTube · Apr 18, 2022
Method 3: Read the ring gear stamps 

1. Locate the ring gear: This requires removing the differential cover to get a clear view of the ring gear.
2. Find the numbers: Look for two numbers stamped on the teeth of the ring gear, such as "41" and "11". 
3. Divide the numbers: Divide the larger number (teeth on the ring gear) by the smaller number (teeth on the pinion gear). 
   • 41÷11≈3.7341 divided by 11 is approximately equal to 3.7341÷11≈3.73 
   • 41÷10=4.1041 divided by 10 equals 4.1041÷10=4.10 

This video shows how to read the ring gear stamps to find the gear ratio: 46sJL LIFE OFFROADYouTube · Nov 18, 2022

What gear ratios are available for an 8 inch Ford?

The Ford 8 inch axle is a smaller version of the popular Ford 9 inch axle, just with an 8 in ring gear diameter, removable pinion support, and typically 28 spline axle shafts. Original gear ratios range between 2.79:1 and 5.43:1, and aftermarket replacement gears are available for many ratios as well.

Which is better, 3.31 or 3.55 axle ratio?

A 3.55 axle ratio is better for towing and hauling because it provides more torque for quicker acceleration and reduces strain on the engine when climbing hills. A 3.31 axle ratio is better for fuel economy on the highway, as it results in lower engine RPMs for a given speed. 
Choose 3.55 if you:

• Prioritize towing or hauling: It gives you more pulling power for heavy loads and reduces the need for frequent downshifting on inclines. 
• Plan to install larger tires: Larger tires can negate the benefits of a 3.31 ratio, and the 3.55 ratio compensates for the added size. 
• Drive in mountainous or hilly terrain: This ratio keeps the engine in its power band on steep grades, even with a heavy load. 

Choose 3.31 if you:

• Prioritize fuel economy: It will generally provide better gas mileage on the highway because the engine runs at a lower RPM. 
• Primarily drive on highways: It's ideal for comfortable highway cruising where you don't need maximum pulling power. 
• Towing needs are moderate: For lighter towing or flat-ground towing, the 3.31 ratio is often sufficient. 

What gear ratio is the Ford 8.8 IRS?

The 8.8 was built with the following ratios: 2.26, 2.47, 2.73, 3.08, 3.27, 3.45, 3.55, 3.73 and 4.10:1. Only the 2.73, 3.08, 3.27, and 3.55:1 ratios were available with Traction-Lok. If you decide to upgrade to a Traction-Lok differential, you're limited to the ratios offered at the factory.