Determining Correct Ring and Pinion Gear Ratio

There’s no way around it. You need to get the right ring and pinion in that ride. You can drag your feet to it, but your vehicle will never run quite the way it should until you get the correct gear ratio.

The good news? You’re not the only person dreading this part of the journey. Making the swap can be a lot of work, and there’s much to learn to get it right. Admit it, though: that’s not what’s freaking you out. It’s the idea of trying to figure out exactly what the right gear is for your combination.

There’s a lot of pressure to nail this selection, as it’s incredibly important to your vehicle’s behavior. Thankfully, it’s also a lot simpler than you might think. You will need to do some brainwork to achieve the perfect setup, but getting yourself in the right ballpark is made easy with some basic math.

What is my gear ratio?

First things first, let’s determine what the existing gear ratio is on your vehicle. There are a few reliable ways to get this number.

• Check your VIN.
  It takes a little decoding, but this handy number provides a wealth of info about your vehicle. You can usually find the VIN on a sticker inside the driver’s side door. While not all VINs contain gear ratio, those that do will have it in the VDS section which are the fourth to eighth digits. Every manufacturer is different, so use a decoder resource like NHTSA or DrivingTests.org to determine what’s what.

• Count your wheel turns.
  If you purchased your vehicle secondhand, and especially if it has aftermarket parts, you’ll want to double-check that the VIN is still accurate. One way is to count how many times the wheel rotates every drive shaft rotation. With blocks under the front tires, the back jacked up, and the entire vehicle in neutral, rotate the rear wheel towards the front and count how many times the driveshaft turns per one complete revolution. For example, 2 ¾ rotations would be a 2.73 gear ratio.

• Divide those teeth.
  A surefire way to find your gear ratio is to remove the differential cover and count the number of teeth on the ring gear and the pinion gear. Then, divide the ring gear’s teeth by the pinion’s teeth. The result? Your gear ratio.

Why change ring and pinion gear ratio?

Since the vehicle’s existing gear ratio may not work with the combination of aftermarket parts you’ve installed, you will need to make some upgrades. The vehicle might have run great when everything was stock, but the ideal gear ratio changes when you install a new cam, alter the engine or transmission, change the tires, or use the vehicle for any kind of specialty driving.

For example, if you perform a lot of highway driving, you want a gear setup to keep you in the best range to deliver the optimal blend of power and efficiency. If you’re driving off-road, something to give max power down low is ideal. And if you’re racing, you want a gear that’ll keep your engine in the rev range where it makes the most power.

Changing tire sizes is an especially common motivator for changing gear ratio. Many times, builders move to an oversized tire only to find that the vehicle feels more sluggish, the shift points change, and the economy drops off. This is because the tires work much like another set of gears that the manufacturers factor into the factory gear ratio. As soon as you change the size, it throws everything off. A new gear ratio is necessary to correct the issues.

How do I determine the right gear ratio for my vehicle?

If you’re one of the many trying to restore your vehicle’s performance after moving to an oversized tire, there’s a simple math problem that will solve your dilemma. Simply take the new tire diameter in inches, multiply it by the original gear ratio, and then divide that number by the original tire size. The number produced represents the “ideal” gear ratio for your vehicle.

That’s a great trick for a quick fix, but it’s flawed. It doesn’t include a number of factors that you’ll need to consider, such as where peak power is made, the rev-range of a particular combination, what speed you’re traveling, and so on. So, even after the sum is found, you might still want to move to a greater or smaller gear ratio.

There’s another formula to consider if you really want to science things out. By multiplying the speed you’ll be traveling, by the presumed right gear ratio, by 336, and then dividing that total number by tire size, you’ll end up with the RPM the combination will bring you to. This formula is very useful for racing applications of all classes, but can also be helpful if you need to figure out a gear ratio that’ll keep your engine in the proper RPM range to deliver good power and fuel economy while cruising.

Make it easy on yourself…

Of course, formulas are great, but there are faster ways to do the math. An RPM calculator is a great tool that you drop your vehicle’s specs into, including the tire size, transmission gearing, and a presumed gear ratio to determine what RPM the engine will turn at a given speed.

You’ll have to play around with any of these methods to find what will work best for your application, but they will all make a massive difference in determining the perfect ratio for your vehicle.

Who should I turn to for my ring and pinion upgrade?

There’s no shortage of suppliers to look to when you finally decide which ring and pinion ratio is best for you. However, it’s likely that Motive Gear is among the names available to your application, and you’ll be hard-pressed to find a better manufacturer to work with.

Motive Gear has been supplying the industry for more than 70 years, and is responsible for keeping countless vehicles on the road as well as giving builders the tools they need to optimize vehicle performance.

With three lines of ring and pinion gears to select from — OE series, Performance series, and Racing Pro Gear — Motive Gear offers a long list of differential components to make the swap. Everything from the gears themselves to the installation kits is built with the best material, and carefully engineered to match the specific demands of each application. Motive Gear believes in its product being among the toughest on the market and is proud to stand behind its offerings with warranties that give you the confidence you deserve behind the wheel. To learn more about Motive Gear, visit: https://www.motivegear.com/