(056) Rotational Inertia

In this video I discuss the implications of heavy moving parts. Not only does apply to internal engine components, but several parts on the car’s exterior. Let me show you exactly why heavy parts are robbing you of speed.

Rotational Inertia – Video Transcript

Hey everybody Matt Covert here again from howtobecomearacecardriver.com. And in this video we’re going to talk about rotational inertia. We touched on this briefly in a video recently called types of engine drag. And we were talking about some internal components of the motor, which kind of deals with this. But we’re going to talk about a couple of things that we didn’t touch on in that video. So let’s go ahead and hop right in on rotational inertia.

I think as a general rule I think it’s probably safe to say that if it’s on your racecar and it spins – I think really the ultimate goal is make that spinning thing accelerate. OK? But here’s the problem with that. Picture for a second, if you will, you have a bowling ball which is just sitting on the floor. And you reach down with one hand and kind of give it a good palm and just give it a spin. And then just kind of let it spin on the floor there OK? Now I want you to do the same thing with a baseball. OK? It’s pretty obvious that the blowing ball is a lot harder to start spinning than the baseball. It’s because it has more rotational inertia. It takes more energy to spin something that weighs more or is bigger.

And I guess in that case the bowling ball is both of those things. OK? And the problem with that is that inside your motor – well, let me go back for a second. Your motor is only capable of producing a certain amount of power. And if that power is being used to try and accelerate heavy components on your car like – let’s say you have really heavy steel wheels. Part of the power from that motor is just being wasted trying to get those wheels to start turning faster. It’s the same concept.

And there are a ton of things on your car which are just robbing power from the engine. So let’s – I mean let’s put that on the list. Wheels. We talk about the crankshaft, that’s a big one. A huge one is flywheels and I’m just going to put clutch under that because those are really heavy assemblies, typically. And I mean you’ve got brake rotors on the outside. And pretty much all the components inside the transmission. And I guess along the same line you’ve got the driveshaft. OK, so you can see there are a lot of things on your car that require power to just – even if they’re – even if they’re already spinning.

It takes a lot of power to get them moving faster. And that’s pretty much what you want when you’re trying to accelerate your car. So a lot of your engine power is going to just getting these things to move faster.

Unfortunately, there isn’t a whole lot you an do about it. OK? Really the only thing you can do is reduce as much weight as possible. Because less inertia equals more power that is available to actually propel the car forward. The faster you can get all your components accelerating – well then the faster your car will accelerate as well.

Not a difficult concept to understand. There isn’t a lot you can do. You’ll notice that most of these things are internal components so in a Street category you can’t change them anyway. But in autocross you can certainly find lighter wheels. That’s a big one. And I think beyond that it’s probably not worth spending money or the effort or anything like that OK?

So just something you have to be aware of – rotational inertia and what it does. If you’re in a full fledged racing category then oh yeah I hope you have some money because reducing weight inside the motor and all that other stuff – it costs a small fortune. And that’s why guys that have the most money always win. I shouldn’t say always. Usually. But that definitely helps.

Alright, I think that’s pretty much all I wanted to say about rotational inertia. Just a little concept you can stick on the back burner. Why don’t you go ahead and click the box down in the corner. That’ll take you right to the YouTube page, you can subscribe there. And make sure you that you get a little notification every time a new one of these videos comes out.

I’m Matt Covert. I’ll be back soon from howtobecomearacecardriver.com with another free video.

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