What is Vehicle’s Crow Ratio Equation?

Let’s Talk About Crow Ratio in Cars

The 2021 Ram Heavy Duty transfer case. The T-Case ratio also is part of the Crow Ratio equation.

Do you know what is the Crow Ratio? Is it the very first time you see such a thing as the Crow Ratio a.k.a CR? Now it’s time to find out what it means and what it does.

 

 

The Crow Ratio is an indirect expression of torque. It means how many times rotations the engine does to rotate the wheels once. As higher the Crow Ratio is the more torque goes at slow speed. The CR is very friendly for the off-road and towing capabilities of the vehicles. Let’s see the equation.

 

An Open Transfer Case | Image: Dana60Cummins 

 

Going through the math to find out what Crow Ratio means. The calculation includes the first gear ratio multiply the T-Case (or the Central Differential) ratio multiply the differential ratio.

 

 

On a video called  How to calculate a vehicle's crawl ratio by SnailTrail4x4 it’s given an example with the stock 1991 Toyota Pickup so that we have:

 

First Gear ratio = 3.954 x T-Case Ratio = 2.28 x Diff. gear ratio = 4.11 that equals 37.05 Crow Ratio.

 

This means that for every 37.05 rotations of the flywheel the tires will have one rotation.

 

If we compared the CR of the 1991 Toyota Pickup to one of the latest SUV models like the 2022 Jeep Grand Cherokee 4xe where its Crow Ratio is 47.4:1.

 

The conclusion about the Crow Ratio is that having a higher Crow Ratio means more torque at a very slow speed. That is very useful while driving off-road and of course when towing.

Question: How to Improve The Crow Ratio?

 

Following the math equation, there are three things to improve for better CR. First, changing the First Gear ratio that goes with changing the gearbox which would be an expensive thing to do, and on another hand, the problem with the mounts will come around – Probably, I would avoid it. Second, it’s less expensive to change the T-Case and/or third changing the differential. Moreover, some people are doing double and triple transfer cases then they go with CR above 1000:1. It’s also very interesting to watch that video How to calculate a vehicle's crawl ratio by SnailTrail4x4 and reading to comments you will find other people who are doing some CR improvements, link below.

 

 

 

If you had watched the video I do have several questions and I’m looking forward to hearing some answers. In the equation, we have the First Gear Ratio, the T-Case ratio, and the differential ratio on the rear axle. Why in the equation the front differential is not included? How the rear differential ratio had changed to 5.29?

 

 

One of the most annoying things about technologies is that all the time a new question comes around. Every question goes to another question and at some point, we made it to how the world is created. As an electrical engineer even more questions come around – why it is that; is it true; is it proven – all day, all night, all the time. Write your comments below.