How do I figure out my gear ratio?

Here's the quick take: for bicycles, gear ratio is the front chainring teeth divided by the rear sprocket teeth; for cars, you use the transmission’s per-gear ratios and multiply by the final-drive ratio. The article below outlines practical steps for both contexts, plus tips for verification and practical use.

Bicycle gear ratios

Simplest setup: one front chainring and one rear cog

This common case lets you calculate a single, straightforward gear ratio and understand how far you move per pedal stroke. Use these steps to determine it and translate it into how it feels on the road.

1. Count the teeth on your front chainring (the crankset you pedal) and on your chosen rear cog.


2. Choose the specific chainring and rear cog you want to evaluate (often the smallest cog with the largest ring is used for a high gear; the opposite is a low gear).


3. Compute the gear ratio: front teeth ÷ rear teeth.


4. Optional but useful: estimate gear development or gear inches. Development = gear ratio × wheel circumference (in meters). Gear inches = gear ratio × (wheel diameter in inches) / 25.4.


5. Test and compare: ride at a steady cadence and note your speed to see how the ratio translates to real-world performance.

In practice, this simple method gives you a baseline for how a given combo behaves and helps you compare different cassettes or chainrings.

Multiple chainrings and cassettes

Most riders use more than one front chainring or more than one rear cog. This adds several possible gear ratios; here’s how to handle the complexity.

1. Identify the front chainring(s) you’ll use and the rear cog(s) you’ll select, noting the teeth counts for each.


2. For each pairing (e.g., 50T front with 12T rear, 34T front with 28T rear, etc.), compute the gear ratio: front teeth ÷ rear teeth.


3. Optionally, calculate gear development for each pairing using wheel circumference to compare how far you travel per pedal revolution in each gear.


4. Organize the results in a small chart to visualize how cadence maps to speed across the gear options, helping you choose the best setup for climbing, sprinting, or flats.

With multiple gears, you can tailor your setup for specific riding styles or terrain. The key is to compare each viable pairing and understand how it changes your cadence and speed at a given effort.

Vehicle gear ratios

Finding and understanding gear ratios from official specs

In cars, gear ratios are published for each gear in the transmission and the final-drive ratio is also listed. This is the easiest official way to know your overall gearing.

1. Look up the manufacturer’s specifications for your vehicle and locate the transmission gear ratios for each gear (1st, 2nd, 3rd, etc.).


2. Find the final-drive (differential) ratio for the same model/year.


3. Compute the overall gear ratio for any given gear: overall ratio = transmission gear ratio × final-drive ratio.


4. Use these figures to understand acceleration, towing capability, and cruising RPM at highway speeds.


5. If you want a quick estimation, some online databases or service manuals provide a ready-made table of these overall ratios.

For most drivers, official specs are the most reliable source. They also let you compare versions of a model (e.g., with different gearboxes) at a glance.

Hands-on measurement method

If you don’t have easy access to official numbers, you can verify gearing by measuring engine RPM and road speed in a given gear, then calculating the implied ratio with wheel size as a reference point.

1. Choose a gear (typically 5th or 6th on a manual or a particular gear in an automatic’s test mode) and drive at a steady speed.


2. Record the engine RPM (via tachometer or OBD-II data) and the vehicle speed (via GPS or speedsometer).


3. Calculate wheel circumference from tire size (circumference ≈ π × tire diameter; diameter can be derived from the wheel and tire dimensions).


4. Infer the overall ratio: engine RPM ÷ wheel RPM (which you get from speed and circumference) gives the gearbox-to-wheels ratio for that gear; compare with published figures if possible.

This hands-on approach can help you verify performance characteristics, but relying on official specs remains the most straightforward method for accuracy.

Summary

Gear ratio is a simple ratio that connects how many teeth are on the driving gear to how many teeth are on the driven gear. For bicycles, it’s front teeth divided by rear teeth, with optional development or gear inches to translate to real-world distance per pedal stroke. For cars, it’s the per-gear transmission ratios multiplied by the final-drive ratio, with the option to validate via measured RPM and speed. Whether you’re tuning a bike or evaluating a vehicle, knowing how to figure out your gear ratio helps you predict performance, plan upgrades, and ride or drive more efficiently.

How do I find out what gear ratio I have?

You can find your gear ratio by checking for a tag on the differential cover, looking at the manufacturer's documentation or sticker, or by doing a "driveshaft turn test". For the turn test, you'll need to jack up one wheel, put the car in neutral, and count how many times the driveshaft rotates for one complete rotation of the tire.
 
This video demonstrates how to check for a gear ratio tag on the differential cover: 1mFlawed OffroadYouTube · Apr 18, 2022
1. Check the vehicle's information 

• Sticker or tag: Look for a sticker inside your glove box or on the door jamb that lists the gear ratio. Many vehicles also have a small metal tag on the differential cover with the gear ratio stamped on it. 
• Vehicle paperwork: Check your original window sticker or build sheet, as this information is often included. 
• VIN decoder: Use a VIN decoder to look up your vehicle's specifications, which may include the gear ratio. 

2. Perform a driveshaft turn test 

• Safety first: Safely jack up the rear of the vehicle and support it with jack stands. Place wheel chocks in front of the front wheels. Do not work under a vehicle supported only by a jack.
• Mark components: Put the vehicle in neutral. Use tape or a marker to make a mark on the driveshaft and another mark on one of the rear tires.
• Spin the wheel: Rotate one of the rear wheels exactly one full rotation (360 degrees).
• Count the driveshaft rotations: While you're turning the tire, count how many full rotations the driveshaft makes. This number is your gear ratio. For example, if the driveshaft rotates four and a half times, your gear ratio is 4.56:1. 

3. Inspect the ring and pinion gears (requires opening the differential) 

• Safety first: This method requires opening the differential, which can be messy and is more involved. Ensure the vehicle is properly supported and the area is clean before proceeding. 
• Find the stamping: Locate the ring gear inside the differential. The gear ratio is often stamped on the side of the ring gear itself, showing the number of teeth on the ring and pinion gears (e.g., "41/11"). 
• Count the teeth: If there is no stamping, count the number of teeth on the ring gear and the pinion gear. Divide the number of teeth on the ring gear by the number of teeth on the pinion gear to get your ratio (e.g., 41÷11≈3.7341 divided by 11 is approximately equal to 3.7341÷11≈3.73). 

You can watch this video to learn how to count the gear teeth: 1mWebWheelerYouTube · Apr 10, 2018

What is the 3.73 gear ratio?

"3.73 gears" refers to a 3.73:1 gear ratio in a vehicle's differential, meaning the engine's driveshaft must turn 3.73 times for the rear wheels to complete one full rotation. This ratio provides a balance between acceleration and fuel efficiency, offering better torque and towing capacity than a lower ratio like 3.21, but not as much as a higher ratio like 4.10. 
What 3.73 gears mean for your vehicle

• Engine RPM: The engine will run at a higher RPM to maintain a certain speed compared to a numerically lower gear ratio, like 3.55. For example, a vehicle with 3.73 gears may be spinning at about 313031303130 RPM at 707070 mph, while one with 3.55 gears would be at a lower RPM. 
• Acceleration and torque: A 3.73 gear ratio provides better off-the-line acceleration and greater torque than a lower gear ratio. This is because it provides a mechanical advantage, making it easier to move heavy loads or larger tires. 
• Top speed and fuel economy: The trade-off for better acceleration is a lower potential top speed and reduced fuel economy at highway speeds. The higher engine RPMs at cruising speed can lead to lower gas mileage. 
• Best use cases: This gear ratio is a good all-around choice for a balance of performance and efficiency. It is a popular option for trucks and SUVs that tow trailers or haul heavy loads, but still need to be comfortable for daily highway driving. 

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

How do I calculate my gear ratio?

To calculate a gear ratio, divide the number of teeth on the output (driven) gear by the number of teeth on the input (driving) gear. You can also use the diameters or radii of the gears for the same calculation: the ratio of the output gear's diameter or radius to the input gear's diameter or radius will give the gear ratio.
 
By number of teeth

1. Identify the gears: Find the driving gear (which is connected to the power source) and the driven gear (which the driving gear turns). 
2. Count the teeth: Count the number of teeth on the driven gear and the driving gear. 
3. Divide: Divide the number of teeth on the driven gear by the number of teeth on the driving gear. 
4. Simplify: Express the result as a simplified ratio, such as 4∶14 colon 14∶1. 
   • Example: If the driven gear has 20 teeth and the driving gear has 5 teeth, the gear ratio is 20÷5=4∶120 divided by 5 equals 4 colon 120÷5=4∶1. 

By diameter or radius

1. Identify the gears: Find the driving and driven gears. 
2. Measure: Measure the diameter or radius of both the driving and driven gears. 
3. Divide: Divide the output gear's diameter or radius by the input gear's diameter or radius. 
   • Example: If the driven gear has a diameter of 4 inches and the driving gear has a diameter of 1 inch, the gear ratio is 4÷1=4∶14 divided by 1 equals 4 colon 14÷1=4∶1. 

0:20How to Calculate Gear Ratio ? #short #3dmechanicaldesign.comYouTube3D Mechanical Design · 2y 2:57Determining Gear Ratio | TOMS OFFROADYouTubeTOMS OFFROAD · 3w 1:27How to calculate gear ratio! Did you know this already? #hotrod ...YouTubeSmithson Speed · 9mo (function(){
(this||self).Bqpk9e=function(f,d,n,e,k,p){var g=document.getElementById(f);if(g&&(g.offsetWidth!==0||g.offsetHeight!==0)){var l=g.querySelector("div"),h=l.querySelector("div"),a=0;f=Math.max(l.scrollWidth-l.offsetWidth,0);if(d>0&&(h=h.children,a=h[d].offsetLeft-h[0].offsetLeft,e)){for(var m=a=0;m