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What is a 3.73 rear axle ratio?

A 3.73 rear axle ratio is a mid-range final-drive gearing in a vehicle’s differential. It means the driveshaft must rotate 3.73 times for every full turn of the wheels, delivering more torque for quicker acceleration and better towing at the cost of higher engine RPM and potentially lower fuel economy on highway driving.

Understanding the figure

The axle ratio expresses how many times the driveshaft turns for one complete rotation of the axle/wheels. A 3.73:1 ratio implies that for each wheel revolution, the driveshaft makes 3.73 revolutions. This gearing multiplies engine torque at the wheels, which helps with launching from a stop and moving heavy loads. It’s important to note that the actual feel of the ratio depends on tire size; larger tires effectively raise the overall gearing, while smaller tires lower it.

Performance and efficiency

The following points highlight the practical implications of a 3.73 rear axle ratio for most drivers. These observations help explain why this gearing is chosen for many trucks, SUVs, and performance-oriented cars.

The 3.73 gearing provides a solid balance between everyday usability and capability. It enhances low-end torque for quicker launches and improved towing, while still allowing reasonable highway performance compared with very high numerical ratios. However, because the wheels turn more slowly than the engines would at the same road speed, engine RPM tends to be higher at highway speeds with this ratio, which can raise fuel consumption and noise on long trips.

Improved initial acceleration and pulling power, useful for towing or hauling.

Higher engine RPM at typical highway speeds, which can reduce fuel economy and increase engine noise over long drives.

Generally lower top-end speed compared with lower-numbered ratios, since the wheels reach higher RPMs needed for very high speeds sooner.

In short, a 3.73 rear axle ratio is a compromise that favors low-speed performance and payload capability without completely sacrificing highway usability.

Choosing the right axle ratio

Selecting a rear axle ratio depends on how you plan to use the vehicle, as well as other drivetrain characteristics. The choice affects acceleration, towing, and fuel efficiency more than any single other feature.

Vehicle purpose: For daily commuting with occasional towing, 3.73 offers a good balance. For primarily highway driving with light loads, a lower ratio (like 3.23 or 3.55) can improve efficiency. For serious towing or off-road use, higher ratios (3.73 or 4.10) may be preferable.

Engine and transmission pairing: Heavier engines or more gears (e.g., 8-, 9-, or 10-speed automatics) can offset some downsides of a higher ratio by optimizing shifts and engine speed.

Tire size: Larger tires effectively raise gearing; smaller tires lower it. When changing tire diameter, you may feel a shift in how the ratio behaves even if the ring-and-pinion remains the same.

Maintenance and availability: Some models offer multiple gearing options as factory choices or as part of trim packages; changing gearing after purchase is possible but involves substantial work and cost.

When weighing options, consider your typical driving profile, including how often you tow, the terrain you encounter, and your highway speeds—these will determine whether 3.73 is the right balance for you.

Common applications

3.73 rear axle ratios are commonly found in mid-range trucks, SUVs, and performance-oriented cars where a blend of confident low-end response and practical highway performance is desired. They are often paired with automatic transmissions that can capitalize on the torque multiplication while maintaining usable cruising RPM under typical driving conditions. For drivers seeking maximum fuel efficiency on long highway trips, a lower numerical ratio is often favored; for those prioritizing towing, acceleration, or off-road capability, 3.73 is a well-known, versatile choice.

Summary

A 3.73 rear axle ratio is a mid-range gear setting in a vehicle’s differential that means the driveshaft turns 3.73 times for every wheel rotation. It boosts torque for better acceleration and towing but typically raises engine RPM at highway speeds, which can affect fuel economy and noise. It’s a balanced option favored in many trucks and SUVs, especially for mixed-use scenarios that require both pulling power and everyday drivability. Tire size and vehicle setup will influence the real-world feel of this gearing, so buyers should consider their typical driving needs when evaluating whether 3.73 is the right choice for them.

What is a 3.73 gear ratio good for?

For a truck, it is great for heavier loads where factory gear ratios that are 3.55 or 3.31. In a sports car, 3.73 gears will offer better acceleration while retaining top speed when compared to 3.55 gears that come factory on many sports cars.

What does 3.73 rear axle ratio mean?

So if a truck has an axle ratio of 3.73:1 or 3.73, it means the driveshaft turns 3.73 times to spin the axle one full cycle. If the driveshaft makes more revolutions to rotate the wheels, the ratio is higher. A higher axle ratio implies higher engine power or torque.

What is the difference between a 3.55 and 3.73 axle ratio?

A 3.73 axle ratio offers better acceleration and towing power, while a 3.55 ratio is better for fuel economy and highway cruising. Choosing between them depends on your priority: opt for 3.73 if you frequently tow heavy loads or want stronger performance, and choose 3.55 if your focus is on better gas mileage during daily driving.

Feature	3.73 Axle Ratio	3.55 Axle Ratio
Acceleration	Faster	Slower
Towing	Stronger and better for heavy loads	Less powerful than 3.73, but adequate for light towing
Fuel Economy	Worse, especially at highway speeds	Better, particularly on the highway
Performance	Higher RPMs for a given speed, better for stop-and-go traffic or hills	Lower RPMs for a given speed, making it more efficient for highway driving
Best For	Hauling, off-roading, or performance-oriented driving	Everyday driving and long-distance highway cruising

What's the best gear ratio for highway driving?

The best gear ratio for highway driving is typically a numerically lower one to keep engine RPMs low, which improves fuel economy and reduces noise. For a vehicle with an overdrive transmission, a ratio like 3.25 to 3.70 is often a good compromise, while a ratio around 3.42 is a common and efficient stock setting for modern vehicles.
This video explains the basics of gear ratios and how they affect performance: 1mGearFX DrivelineYouTube · Feb 10, 2023
Common gear ratios for highway driving

3.25: A good choice for pure highway cruising and long road trips, especially with a non-overdrive transmission, as it keeps RPMs very low.
3.42: A popular and well-balanced ratio often found in factory vehicles, offering a good blend of fuel economy and acceleration for daily driving.
3.55: A good option for prioritizing fuel economy on the highway, though it sacrifices some acceleration compared to higher ratios.
3.70: A strong compromise that provides a good balance between highway cruising and better acceleration for daily driving or occasional spirited driving.

Factors to consider

Transmission: Vehicles with an overdrive gear (where the driveshaft spins faster than the engine's output shaft) can use a numerically lower gear ratio and still achieve low highway RPMs.
Tire size: Taller tires require a numerically lower gear ratio to avoid excessively high RPMs at highway speeds.
Engine and vehicle weight: A more powerful engine or a lighter vehicle can handle a numerically higher ratio without a significant penalty to highway performance, while heavier vehicles may need numerically lower gears for better performance.
Driving goals:
- Maximum fuel economy: Go with the most numerically low ratio possible.
- Balance of fuel economy and acceleration: Choose a ratio in the 3.55 to 3.70 range.
- Frequent towing or heavy loads: You will generally want a more numerically high gear ratio for more torque, but this will result in higher RPMs on the highway.

This video explains how to choose the right gear ratio for your vehicle based on your needs: 56sLate Model Restoration (LMR)YouTube · May 18, 2025

Kevin Bennett

Company Owner

Kevin Bennet is the founder and owner of Kevin's Autos, a leading automotive service provider in Australia. With a deep commitment to customer satisfaction and years of industry expertise, Kevin uses his blog to answer the most common questions posed by his customers. From maintenance tips to troubleshooting advice, Kevin's articles are designed to empower drivers with the knowledge they need to keep their vehicles running smoothly and safely.