What is my rear end gear ratio?

The rear-end gear ratio is the numeric figure that links engine speed to wheel speed through the differential. It is the number of engine revolutions required for one wheel revolution; for most street cars the ratio typically falls in the 2.73 to 4.10 range, with heavier-duty trucks sometimes exceeding that (up to around 4.56). The exact figure is usually listed in factory documentation or can be determined by inspecting the axle or counting gear teeth.

Where to find your rear-end gear ratio

Most vehicles publish the axle ratio in a few standard places. Start with the simplest sources before attempting any internal measurements.

• Door jamb placard or owner’s manual listing drivetrain details, including the axle ratio.


• Differential or axle tag on the rear axle (stamped or stamped-and-painted code indicating the ratio).


• Factory build sheet or window sticker (RPO/options) that specify the installed axle.


• VIN lookup through a dealer or manufacturer website, which can provide the axle ratio in the vehicle’s data.


• Service manuals or the dealer’s service department can confirm the ratio from the axle code if you provide the VIN.

If you can’t locate any of these sources, contact your dealership or a qualified mechanic. The axle ratio matters for towing, gearing changes, and understanding fuel economy, and it normally does not change over the life of the vehicle unless you alter tires or gears.

How to determine the ratio yourself

If you want a hands-on method, you can determine the final drive ratio by measuring gear teeth or by using a measurement method that doesn’t require full differential disassembly. The approaches range from simple to more involved—and come with safety caveats.

Count the teeth on the ring gear and pinion (requires access to the differential)

Before attempting this method, ensure you have the proper tools, the vehicle is secure, and you’re comfortable working on the drivetrain. If in doubt, use the official sources above.

1. Park on a level surface, engage the parking brake, and place wheel chocks around the tires.


2. With the transmission in neutral, rotate the driveshaft by hand to bring the ring gear into view, then drain and remove the differential cover to access the gears. Wear eye protection and follow fluid disposal rules.


3. Count the number of teeth on the ring gear (the larger gear) and on the pinion gear (the smaller gear). If needed, take multiple counts to confirm.


4. Compute the ratio by dividing the ring gear teeth by the pinion gear teeth (Ratio = Ring Teeth ÷ Pinion Teeth). For example, 41 ring teeth and 11 pinion teeth yields 3.73:1.


5. Reinstall the differential cover with a new gasket or sealant as needed, refill with the proper gear oil to spec, and clean up any spilled fluid.


6. Test drive to ensure nothing leaks and that the oil level is correct after reassembly.

Note: On many modern vehicles, the differential cover is sealed or the axle is not intended to be disassembled by the owner. If you are unsure, rely on the official sources or have a professional perform this check. Also, be aware that changing tire size effectively changes the overall gearing that the drivetrain experiences, even if the axle ratio remains the same.

Alternative method: verify using vehicle data or diagnostics

Some vehicles provide the final drive ratio through onboard diagnostics or service tools. A dealer-level scan tool or official online data portal may display the axle ratio or final-drive specification without opening the differential. This method is safer and quicker for many modern vehicles.

When in doubt, consult the dealer or a certified mechanic, especially if you plan to modify gearing or tow heavy loads.

Why the rear-end gear ratio matters

The ratio affects acceleration, highway cruising RPM, fuel economy, towing capability, and even tire wear. A lower numerical ratio (e.g., 2.73) yields lower engine RPM at highway speeds and typically better fuel economy but slower acceleration. A higher ratio (e.g., 4.10) provides stronger acceleration but higher engine RPM at cruising speeds, which can reduce fuel economy and increase engine noise. After changing tire size or gearing, expect changes in performance characteristics and the need to recalibrate the speedometer reading.

Summary

The rear-end gear ratio is the essential figure that connects engine speed to wheel speed through the differential. You can determine it from an axle tag, VIN or build sheet, or by counting ring and pinion teeth if you’re comfortable with drivetrain work. In many cases, your vehicle’s documentation will give you the exact number; knowing it helps with maintenance, towing, performance tuning, and understanding fuel economy. When in doubt, verify with manufacturer documentation or a qualified technician.

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. 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. 2. Mark the driveshaft and a tire: Place a mark on one of the rear tires and a corresponding mark on the driveshaft. 
3. 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. 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. 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. 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. 1. Locate the ring gear: This requires removing the differential cover to get a clear view of the ring gear.
2. 2. Find the numbers: Look for two numbers stamped on the teeth of the ring gear, such as "41" and "11". 
3. 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

Where is the gear ratio stamped?

So let's zoom in here. You see that right there reads 411 which means 41 ring gear teeth 11 pinion teeth 41 divided by 11. Gives you 3.727.

Does the VIN number tell you the gear ratio?

You may be able to tell the gear ratio from a vehicle's VIN by using an online VIN decoder, though not all manufacturers include this information in the VIN itself. If the gear ratio is included, it will likely be in the Vehicle Descriptor Section (VDS), which are the 4th through 8th digits of the VIN. For many vehicles, a sticker on the driver's side door jamb or on the vehicle's build sheet or owner's manual is a more reliable way to find the gear ratio. 
How to check the VIN

• Use an online VIN decoder: Enter the full VIN into a free online decoder. Some manufacturers have their own decoders, such as Mopar's decoder. 
• Look for the gear ratio code: Some VINs will have a code within the VDS that represents the gear ratio (e.g., "3731"). 
• Consult the manufacturer: If the VIN decoder doesn't provide the information, contact the vehicle manufacturer for assistance. 

Other methods to find the gear ratio

• Check the vehicle sticker: Look for a sticker on the driver's side door jamb or on the vehicle's build sheet. This sticker often contains detailed information about the vehicle's equipment, including the axle ratio. 
• Look at the differential: Some differentials have a metal tag with the gear ratio stamped on them, or there may be a sticker on the axle itself. 
• Consult your owner's manual: The owner's manual or other paperwork from the vehicle's purchase often lists the gear ratio. 

How do I find my rear end gear ratio?

You can determine a rear end gear ratio by checking for a data tag on the differential cover, manually spinning a rear wheel to count the driveshaft rotations, or inspecting the ring and pinion gears for tooth counts. The simplest method is to look for a tag, while manual rotation is a good alternative without opening the differential. For the most definitive answer, you can remove the differential cover and divide the number of teeth on the ring gear by the number of teeth on the pinion gear.
 
This video explains how to find the gear ratio by spinning the wheels: 59sWebWheelerYouTube · Apr 10, 2018
Method 1: Check the differential cover tag 

1. Locate the differential cover on the rear axle. 
2. Look for a metal tag, often attached to one of the bolts. 
3. Clean the tag to read the numbers, which will be the gear ratio (e.g., "3.73" or "410" for 4.10). 

Method 2: Manually rotate the wheels 

1. Safely jack up the rear of the vehicle so the rear wheels are off the ground. 
2. Place the transmission in neutral. 
3. Mark the driveshaft and one of the rear wheels with tape or chalk. 
4. Rotate the marked rear wheel one full rotation. 
5. Count how many times the driveshaft rotates during that one full tire rotation. 
6. The gear ratio is approximately equal to the number of driveshaft rotations. For example, if the driveshaft turns 3.73 times, the ratio is 3.73:1. 

This video demonstrates how to count the gear ratio by spinning the wheels: 1mklowny1969YouTube · Nov 4, 2015
Method 3: Count the teeth on the gears 

1. Safely jack up the vehicle and remove the differential cover to access the ring gear. 
2. Find the stamping on the side of the ring gear, which shows the number of teeth. 
3. Locate the smaller pinion gear and count its teeth. 
4. Divide the number of ring gear teeth by the number of pinion gear teeth. The result is the gear ratio. 

This video shows how to count the gear teeth to determine the gear ratio: 58sLet's Build a Willys JeepYouTube · Jan 24, 2023