What does 3.92 axle ratio mean?

In practical terms, a 3.92 axle ratio means the driveshaft must turn about 3.92 times for every full wheel revolution, boosting torque and towing capability while increasing engine RPM at highway speeds and reducing fuel economy relative to lower final-drive ratios.

Understanding axle ratios and where 3.92 fits

Axle ratio is the gear reduction inside the differential. The 3.92:1 ratio indicates the driveshaft rotates 3.92 times for each wheel rotation, multiplying engine torque at the wheels. Vehicles use this ratio to trade off acceleration and pulling power against top speed and efficiency.

Key effects on performance

These are the primary performance implications you’ll notice with a 3.92 final drive, assuming standard tire size and typical transmission behavior.

• Stronger low-end torque and improved launch feel, especially when starting from a stop or pulling a load.


• Better hill-climbing ability and towing performance due to greater torque multiplication.


• Higher engine RPM at a given highway speed, which can improve power availability but increase noise and wear over long trips.


• Generally lower fuel economy on sustained highway cruising compared with lower final-drive ratios and identical engine setups.

In practice, these tradeoffs matter most if you frequently tow, haul heavy loads, or drive in mountainous terrain.

Practical considerations when using a 3.92 ratio

Before deciding whether 3.92 is right for you, consider how wheel size, transmission, and typical driving will interact with the ratio.

• Tire size effects: Changing tire diameter alters the effective gearing. Larger tires slightly reduce engine RPM at a speed, partially offsetting the 3.92’s high-rpm tendency; smaller tires increase rpm and can magnify it.


• Transmission pairing: Automatic versus manual transmissions, torque converter behavior, and gear spread affect how the ratio feels in real-world acceleration and fuel use.


• Use case: If you regularly tow trailers, off-road, or haul heavy payloads, 3.92 is often preferred for its torque advantages; for long highway commutes, a lower ratio may save fuel.


• Fuel economy impact: Expect a modest drop in highway mpg when the ratio is higher, particularly at higher speeds and with smaller tires.

Understanding these factors helps drivers decide if a 3.92 ratio aligns with their driving goals and vehicle type.

Estimating engine speed at a given speed

To compare gearing across vehicles, you can estimate engine RPM at a given road speed using tire size, final drive, and transmission gear. The following rough formula gives a convenient rule of thumb.

RPM ≈ MPH × 1056 ÷ (tire_diameter_in_inches × π) × final_drive_ratio × transmission_gear_ratio

Note: This is a simplified estimate. Real-world numbers vary with tire wear, exact tire circumference, gear counts, and throttle load.

Summary

A 3.92 axle ratio prioritizes torque and towing capability over highway fuel efficiency. It provides stronger launch and better climbing performance but increases engine speed at cruising speeds, which can lift fuel use and noise. When evaluating a vehicle or considering aftermarket gearing, weigh how often you tow or drive in hilly terrain versus your highway commuting needs. The key is to match the final drive to your typical driving profile and vehicle capabilities.

Which is better, 3.73 or 4.10 axle ratio?

Neither 3.73 nor 4.10 gears are inherently "better"; the choice depends on your driving priorities. 4.10 gears provide quicker acceleration and more torque, which is ideal for performance or heavy towing, but at the cost of lower fuel economy and higher engine RPMs at highway speeds. 3.73 gears offer better fuel economy and a higher top speed because the engine runs at a lower RPM on the highway, making them better for general cruising and long-distance driving. 
You can watch this video to see the difference in acceleration between 3.73 and 4.10 gears: 56sTheKingCoopaYouTube · Dec 17, 2021
4.10 gears

• Pros:
  • Quicker acceleration and a faster feel off the line. 
  • More torque, making them better for towing heavy loads. 
• Cons:
  • Lower fuel economy. 
  • Higher engine RPMs at highway speeds, which can lead to more engine noise. 

3.73 gears 

• Pros:
  • Better fuel economy. 
  • Higher top speed because the engine runs at lower RPMs on the highway. 
  • Quieter and more comfortable for highway cruising. 
• Cons:
  • Slower acceleration compared to 4.10 gears. 
  • Less torque for towing. 

This video demonstrates the difference in cruising speed RPMs between 3.73 and 4.10 gears: 1m2Val_bYouTube · May 29, 2020
How to choose

• Choose 4.10s if: Your priority is performance, and you want a vehicle that feels quick off the line. They are also a good choice if you frequently tow heavy loads. 
• Choose 3.73s if: Your priority is fuel economy and comfortable, quiet highway cruising. They are a better all-around choice for a daily driver or a vehicle that spends most of its time on the open road. 

How to tell if RAM has 3.92 rear axle ratio?

You can tell if a Ram has a 3.92 rear axle ratio by checking the vehicle's original window sticker, looking for a metal tag on the rear differential, or by entering the VIN into an online decoder. Another method is to check the build sheet, which may be located under the hood or can be accessed through the Ram app. 
This video explains how to check the gear ratio of your vehicle: 59sWebWheelerYouTube · Apr 10, 2018
Method 1: Check the tags and stickers 

• Differential cover tag: Look for a small metal tag attached to one of the bolts on the rear differential cover. It will have the gear ratio stamped on it, such as "3.92".
• Axle sticker: There may be a sticker on the axle itself that indicates the ratio. 

Method 2: Use your Vehicle Information

• Original Window Sticker: Look up your original window sticker online by using your VIN. Many websites allow you to do this for free. 
• VIN Decoder: Enter your vehicle's VIN into an online VIN decoder to get the full build sheet, which will include the axle ratio. 
• Ram App: Download the official Ram app. The vehicle's equipment information, including the axle ratio, can often be found in the digital glove box or vehicle equipment section. 
• Build Sheet: If you have a physical build sheet, it will contain the axle ratio information. 

Method 3: On-vehicle inspection (if tags are missing)

• Mark and spin: This is a more old-school method. With the truck on a lift, mark the driveshaft and a single rear wheel. Rotate the wheel one full revolution and count how many times the driveshaft rotates. A 3.92 ratio means the driveshaft will spin slightly over 4 times for one wheel rotation. 

What axle ratio is best for towing?

For heavy-duty towing, an axle ratio with a higher numerical value, such as 3.73 or 4.10, is best because it provides more torque for pulling power, though it results in lower fuel economy. For occasional towing or a balance between power and fuel efficiency, a ratio like 3.55 is a good compromise. 
Axle ratios for towing

• 3.73 or higher (e.g., 3.90, 4.10): Use this for your primary towing vehicle if you are regularly towing heavy loads. A higher ratio provides more torque, making it easier for the engine to pull heavy trailers, especially on hills. 
• 3.55: This is a good "middle-of-the-road" ratio, suitable for both occasional towing and daily driving. It provides a balance of towing capability and fuel efficiency compared to higher ratios. 
• 3.21 or lower (e.g., 3.42): These lower ratios are generally better for fuel economy when not towing. They are not recommended for heavy towing, as they put more stress on the engine and drivetrain. 

How to choose

• Determine your towing needs: If you tow frequently or have a very heavy trailer, a higher numerical ratio is a good choice. 
• Consider your other use: If your truck is a daily driver and you only tow occasionally, a ratio that offers a better balance of fuel economy and towing power, like 3.55, will likely be a better fit. 
• Factor in engine and transmission: Newer transmissions with more gears (like 8- or 10-speed automatics) can make lower axle ratios more capable, as the lower gears can help compensate for the lack of torque. Similarly, a diesel engine already has high torque, which might allow you to use a lower axle ratio and still tow effectively. 

What's the best rear-end gear ratio?

There is no single "best" rear end gear ratio, as the ideal choice depends on the vehicle's intended use, with higher numbers like 4.104.104.10 providing better acceleration and a lower ratio like 3.253.253.25 offering better highway fuel economy. A numerically lower ratio (e.g., 3.253.253.25) is best for highway cruising because it allows the engine to run at lower RPMs for better gas mileage. A numerically higher ratio (e.g., 4.104.104.10) is best for performance and towing because it improves acceleration by letting the engine work less to start moving a heavy load. A ratio in the mid-range (e.g., 3.553.553.55 to 3.733.733.73) is often considered a good compromise for daily driving that can still handle some towing or spirited driving. 
Performance and towing (numerically higher ratios) 

• Best for: Frequent heavy towing, off-roading, drag racing, or maximizing acceleration. 
• How it works: Higher numbers mean the driveshaft has to turn more times for each rotation of the wheel. This gives the vehicle more "pulling power" from a stop, but results in higher engine RPMs at highway speeds, decreasing fuel economy. 
• Examples: 4.104.104.10, 4.564.564.56, or higher for specialized use like drag racing. 

This video explains what gear ratios are and their impact on acceleration: 59sTCcustomsYouTube · Mar 4, 2020
Highway and fuel economy (numerically lower ratios) 

• Best for: Primarily highway driving where fuel efficiency is a priority. 
• How it works: Lower numbers mean the driveshaft turns fewer times for each wheel rotation. This reduces engine RPMs at higher speeds, improving fuel economy, but results in slower initial acceleration. 
• Examples: 3.083.083.08, 3.253.253.25, or 3.553.553.55. 

Balanced daily driving (mid-range ratios) 

• Best for: A mix of city and highway driving, or for a compromise between acceleration and fuel economy.
• How it works: This offers a middle ground, providing decent acceleration for daily use while keeping highway cruising RPMs from getting too high.
• Examples: 3.553.553.55 or 3.733.733.73. 

Other factors to consider

• Transmission: The type of transmission (e.g., automatic with overdrive vs. manual) greatly affects the choice of gear ratio. A transmission with a high-gear overdrive ratio can allow for a lower (numerically higher) axle ratio without sacrificing highway fuel economy. 
• Tire size: Larger tires require a lower (numerically higher) gear ratio to maintain performance, as they have a larger diameter, which is the same as changing the gearing. 
• Engine specifics: The engine's torque curve and horsepower band, as well as the vehicle's camshaft specifications, all influence the ideal gear ratio.