Gearing Calculator. Upgrading the differential in your BMW is one of the best ways to improve handling, acceleration, and all-around performance. Whether you're looking to alter the final drive gear ratio, or add limited-slip functionality to get all that power to the ground in the turns, we've got the knowledge to guide you in the right direction. There are two types of differentials found in BMWs. In the majority of non M cars, the differential that came in your vehicle from the factory are called an open differential.
In most M cars, your vehicle came from the factory with a limited slip differential. See descriptions on each type below.
Open Differential: An open differential is the simplest type of differential. When a car is driving in a straight line, both drive wheels are spinning at the same speed. The pinion gear turns the ring gear and carrier and none of the pinions within the carrier are rotating—both side gears are effectively locked to the carrier. An open differential will always apply the same amount of torque to each wheel. There are two factors that determine how much torque can be applied to the wheels: equipment and traction.
In dry conditions, when there is plenty of traction, the amount of torque applied to the wheels is limited by the engine and gearing; in a low traction situation, such as when driving on ice, the amount of torque is limited to the greatest amount that will not cause a wheel to slip under those conditions. So, even though a car may be able to produce more torque, there needs to be enough traction to transmit that torque to the ground.
If you give the car more gas after the wheels start to slip, the wheels will just spin faster. Now what happens if one of the drive wheels has good traction, and the other one is on ice?
This is where the problem with open differentials comes in. Remember that the open differential always applies the same torque to both wheels, and the maximum amount of torque is limited to the greatest amount that will not make the wheels slip. It doesn't take much torque to make a tire slip on ice.
And when the wheel with good traction is only getting the very small amount of torque that can be applied to the wheel with less traction, your car isn't going to move very much.
The solution to these problems is the limited slip differential. Clutch Type: The clutch-type LSD is probably the most common version of the limited slip differential. This type of LSD has all of the same components as an open differential, but it adds a spring pack and a set of clutches.
Some of these have a cone clutch that is just like the synchronizers in a manual transmission. The spring pack pushes the side gears against the clutches, which are attached to the carrier. Both side gears spin with the carrier when both wheels are moving at the same speed, and the clutches aren't really needed -- the only time the clutches step in is when something happens to make one wheel spin faster than the other, as in a turn.
The clutches fight this behavior, wanting both wheels to go the same speed. If one wheel wants to spin faster than the other, it must first overpower the clutch. The stiffness of the springs combined with the friction of the clutch determine how much torque it takes to overpower it. Getting back to the situation in which one drive wheel is on the ice and the other one has good traction: With this limited slip differential, even though the wheel on the ice is not able to transmit much torque to the ground, the other wheel will still get the torque it needs to move.
The torque supplied to the wheel not on the ice is equal to the amount of torque it takes to overpower the clutches. The result is that you can move forward, although still not with the full power of your car.The rear axle gear ratio is the number of turns that the input of the differential at the driveshaft makes in relation to its output at the rear wheels.
Different gear ratios can have different effects in the way a vehicle performs. If you have ever wondered what the gear ratio is in your rear-wheel drive vehicle and the factory axle tag is missing, there is a simple method of calculating this without disassembling the rear axle. Slide a floor jack under the rear of the vehicle and raise it until the rear wheels are off the ground. Place jack stands under the rear axle on both sides of the vehicle. Lower the jack so the weight of the rear of the vehicle is supported by the jack stands.
Crawl under the vehicle and locate the drive shaft where it attaches to the front of the rear axle. Place a 6 to 8 inch length of masking tape longitudinally on the drive shaft where it will be easily visible from the side of the vehicle near one of the rear wheels. Rotate the tire by hand one complete revolution using the piece of masking tape on the tire as a guide.
Count the number of revolutions the drive shaft turns using the masking tape attached to it as a guide to one tire revolution. For instance, if the drive shaft rotates three and a quarter turns to one tire rotation, then your rear axle gear ratio is 3. Remove the masking tape from the drive shaft and tire. Raise the rear of the vehicle with the floor jack and remove the jack stands. Lower the floor jack until the rear wheels are on the ground.
Step 1 Slide a floor jack under the rear of the vehicle and raise it until the rear wheels are off the ground. Step 2 Crawl under the vehicle and locate the drive shaft where it attaches to the front of the rear axle. Step 3 Place a piece of masking tape on the edge of one of the rear tires.
Step 4 Rotate the tire by hand one complete revolution using the piece of masking tape on the tire as a guide. Step 5 Count the number of revolutions the drive shaft turns using the masking tape attached to it as a guide to one tire revolution. Tip You can pinpoint the exact rear axle gear ratio of your vehicle by finding out what axle ratios were available for your particular vehicle from the owner's manual or a repair manual.
Using the example in the above procedure, if ratios 2. Items you will need Floor jack Jack stands 2 Masking tape. References Jedi: What's my Gear Ratio?How do you determine what gear ratio you have? Sages will tell you to look for numbers on the case, which is great if: a. If you block one, the other wheel spins twice as quickly. When driving, this allows the wheel on the inside of a turn to rotate slower than the one on the outside of the turn. With the transmission in neutral, rotate the unblocked wheel two full turns and note how many times the pinion flange of the differential rotates.
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Marking the wheel and flange with a white marker helps keep track of the rotations. The number of turns is the gear ratio, which is called out as number of turns of the differential pinion to one turn of the axle. So why is this number important? The lower the number, the faster the car will go with the same number of engine revolutions. The higher the number the better the car will accelerate, but at the expense of high speed cruising. Now for the confusing part of the story.
A high numerical gear ratio is called a low gear or low rear end, and vice versa. Low gears give fast acceleration, high gears give better cruising. A smaller engine will need a lower rear end to give adequate acceleration. A more powerful engine can use a higher rear end to give relaxed cruising and a higher top speed.
So if you install a bigger, more powerful engine you probably want to change to a higher gear ratio from stock. Shorter tires require a higher gearing to travel the same distance as a taller tire, so as tire sizes got smaller and engines produced more power, the gear ratios tended to get higher.
Tagged: Kelvin Dodd. November 13, May 4, October 21, pm Gilbert. December 20, pm Phil. November 3, am Sam. This is hilarious.You typically hear people talking about gearing or gear ratios when speaking about muscle cars.
Gear ratios can be changed in many vehicles, which can result in a change in the way that your vehicle drives. The gear ratio is determined by the final drive gears that are installed in your vehicle. If you plan on doing any upgrades on your car or truck, knowing how to determine what the gear ratio is can help you to make an educated decision when making changes to your drivetrain. When talking about gear ratios, it is important to know that all vehicles have a gear ratio designed into the drivetrain of the vehicle.
This ratio cannot be changed on most front wheel drive vehiclesbut can be changed on many rear wheel drive vehicles. The gear ratio is the difference in the size of the pinion gear, or input gear, and the ring gear, or output gear. An example of this would be a gear ratio of This would mean that the input gear would have two revolutions and the output would have one revolution. This results in a multiplication of torque, or the turning force at the wheels.
This can affect the vehicle in many different ways:.
How to Calculate the Rear Axle Gear Ratio
A lower gear ratio can affect fuel mileage by decreasing engine RPM at highway speeds. Gear ratios can be changed to compensate for changes in tire size. There are several ways to determine the gear ratio on your vehicle. It is important to have all of the correct materials and safety equipment prior to checking the vehicle.
There are two different ways to determine your gear ratio.
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One of the methods will tell you the exact gear ratio and the other will give you an approximation. In both instances, you will prepare the vehicle the same way. Step 3: Using the floor jack, lift the vehicle at the manufacturer's recommended lifting points. Raise the car until the back tires are off the ground. Step 4: Place the jack stands under the jacking points. Then lower the vehicle onto them.
Step 5: Put the vehicle into neutral so that you can spin the driveshaft by hand. Step 1: Place a visible mark on the driveshaft near the differential housing. Use the chalk or paint pen. Also place a mark on the back of one of the rear tires.Can Gearing Make Your Car Faster? With Proof!
Step 2: Spin the driveshaft by hand. While spinning the driveshaft, count the revolutions by watching the markings, as well as counting the revolutions of the tire at the same time. Step 3: Continue spinning the driveshaft. Keep counting the rotation of the marks you have made, until you feel like you have a good record of each rotation.
Step 4: Divide the number of revolutions of the driveshaft by the revolutions of the tire. This will give you your approximate gear ratio. This is the most accurate method of determining your gear ratio. Most gear ratios are not exact numbers, making the spinning method less accurate.Our Differential Gear Ratio Calculator can help you select the correct gear ratio to maximize the performance of your vehicle. The addition of larger tires can greatly decrease performance and fuel economy.
Choosing the right differential gear ratio will help regain lost power and torque. You need to know your tire diameter in order to work with the RPM calculator relevant to gear ratio. Inaccurate tire size input will greatly affect the results from the Gear Ratio Calculator.
How to Figure Out the Gear Ratio of Your Car
The calculated value should be used only as a guideline for RPM calculations. Quite often, if you measure your tire diameter from the ground to the top of the tire, it measures less than the calculated value. Tires with identical specifications that are made by different manufacturers may also have different actual diameters.
You can try various combinations to come up with an appropriate combination of ring and pinion gear ratio and tire diameter for your vehicle. The RPM calculator should be used as a guideline for comparative purposes only. Differential Gear Ratio Calculators Our Differential Gear Ratio Calculator can help you select the correct gear ratio to maximize the performance of your vehicle.
The Tire Diameter Calculator will allow you to determine your actual tire diameter. The Gear Ratio Calculator will determine the ratio of a gear set, based on the number of teeth on the ring gear and teeth on the pinion gear. This is especially helpful when trying to identify a gearset that needs replacement with the same ratio ring and pinion.
Tire Diameter Calculator. Tire Width mm. Aspect Ratio Tire Series. Wheel Size inches. The Tire Diameter:. RPM Calculator.
Gear Ratio. Tire Diameter. Gear Ratio Calculator.
Ring Gear:. Pinion Gear. Your gear ratio is.Use our Differential Gear Ratio Calculator page to determine the best ring and pinion gear ratio for your vehicle. Installation of the correct ring and pinion gear ratio will help optimize performance, fuel economy and overall driveability. In order to select the ideal differential gear ratio, the first thing you will need to know is your actual tire diameter.
The simplest method is to measure the height of the tire from the ground to the top of the tire. The calculated value should be used only as a guideline for RPM calculations. Need help? Our gear and axle experts will be happy to assist at You can try various combinations to come up with an appropriate combination of ring and pinion gear ratio and tire diameter for your vehicle. The RPM calculator should be used as a guideline for comparative purposes only.
Find all of the gear ratios available for your vehicle in our Application Guides. We have the Differential Gears to match your budget and performance needs. Enter the number of teeth on your ring and pinion gear set to find the gear ratio. For inquiries about our products and services, please fill out the form below.
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Your Message. Skip to content Featured Products and Specials. Differential Gear Ratio Calculator. Tire Width mm. Aspect Ratio Tire Series. Wheel Size inches. The Tire Diameter:.
RPM Calculator. Gear Ratio. Tire Diameter.Use our gear ratio calculator to find the changes to gear ratio when going to a different tire size.
Both the effective and new gear ratios are calculated. Use our gear ratio calculator to find the effective gear ratio your vehicle will have with a new tire size. Also calculated is the new gearing you would need in order to return back to your original gear ratio when going to a bigger or smaller tire.
Input your stock and new tires sizes along with your original gear ratio. Click "Calculate" to find your new effective gear ratio and the gear ratio needed to return your vehicle back to stock gearing. Changing tire size will ultimately affect the power and drivability of your vehicle.
If you are looking to retain your stock feel or change your gearing to the optimal ratio, then you will need this gear ratio chart to do so. Using the chart, first cross reference your current gear ratio and tire diameter to find your approximate RPM at 65 MPH.
Then reference your new tire diameter with your choice of RPM to find the new gear ratio needed to supply you with that RPM. This chart is based on a drive gear of at 65 MPH using a manual transmission. Automatic transmissions will run a slightly higher RPM do to slippage.
If you are using the calculated diameter, multiply that number by. If you are measuring your tire, measure from flat ground up to the center of the hub and multiply that number by 2. Gear Ratio 2. Tire Size Tools. Tire Categories. Popular Sizes.