Polar Moment of Inertia

Polar Moment of Inertia

In this video I tackle an interesting and important physics concept – polar moment of inertia. Not only will this add value to your motorsport knowledge base, but it will show you why vehicle weight distribution is so important.

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Video Transcript

Hey everyone, Matt Covert again here from howtobecomearacecardriver.com, with another free video in the series. I’m super pumped to keep this thing going, and I want to talk for a brief few moments about polar moment of inertia.

And we’re getting into some kind physics stuff now, but I think it’s really important to understand all these little concepts cause when you do all that knowledge adds up and it allows you to analyze and think about different things in the racecar world which can ultimately benefit you.

So let’s take a look at what this is. Polar moment, let’s just say, a moment a moment in physics is loosely defined as an object’s to rotate about itself. OK, so with that in mind, let me show you what I’m talking about.

Let’s just say we have, I’ll just make that a little straighter, let’s just say we have a board here and there’s a pivot point of some kind in the middle, and let’s say we have a couple weights that are way out on the end here. Let’s say this is, like, an eight foot board or something like that.

Well, the farther away a weight is from a pivot point, the harder it is for these weights to change direction. So let’s say, let’s say that you wanted to pivot this board back and forth like this. Well it takes a lot more effort to change the direction of the weights if they’re way all the way out here. OK? Let me go back a little. Now let’s move the weights further inside like this, same weight on the same situation, but when you’re trying to move them back and forth now it becomes pretty easy because they’re closer to the pivot point. That’s the basic idea of the polar moment of inertia in a racecar.

And this is directly applicable to racing vehicles so let’s draw a couple tires here. This would be looking on from, say, the front end of a car, OK? On a typical vehicle you’ve got all kinds of stuff going on in this area next to the wheel. You’ve got the brake assembly and the hub assembly, whatever all that stuff looks like. You’ve got all the suspension components and all that kind of thing.

So on really serious racecars, and I’m talking really serious racecars, like the Factory Five, whatever their ’33 Ford is, they were clever enough to do this, they moved all these suspension components further inward. So all that stuff is mounted, like the shock is mounted, the shock and spring assembly it’s actually mounted up here and it’s connected to the wheels through some kind of linkage. And it’s like that on both sides.

Well this car has a better polar moment of inertia now because all that weight has been moved from out here inside toward the center and that allows the vehicle to change directions more quickly, just like this simple fulcrum system like this.

And it’s the same story, I know that a lot of Alpha Romeos, a lot of older ones, they moved their brake assemblies from here, and they moved them further inward so the brakes and rotors and such are actually mounted in the middle toward the center of the drive axle. And they did that going the other way too, they were really clever. Let me just draw the four tires here. And they would do that on both axles.

So now you’ve got all this weight moved in toward the middle, which is great. It increases the handling and increases the cars ability to go from flat to when it’s cornering and it changes from this to this much quicker simple because it has a better polar moment of inertia.

And I’m going to end there and move on to something else, I’ll go make another video, I’m totally on a roll. So if these videos are helping you all, helping you out at all and you like them. I really like this set up with the chalkboard and drawing on the screen, it’s really kind of fun. So if it’s something that’s helping you out please go down and hit the subscription button, I’ll put on up on the screen, you can go over to the channel and see what other kinds of videos are up there. They’re all free and I hope you enjoy. And I’ll be back soon with another video from howtobecomearacecardriver.com. Take care.

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