Nerdy Question.......

[rwh11385]

How come no one finds the moment of inertia for wheels/tires? It would be a lot better to compare the differences in packages and acceleration.....

[bwanac]

Becuase it is so complicated. Look at the distribtion of the mass! So many different options, might be a little tricky to find. Plus we got friction involved. Might not even matter with that.

Unless if you are talking about manufacturers using a machine to find it, then it would make sense.

Just some crazy ramblings.

[E30godz]

i believe it would be very hard to determine the amount of mass at the circumference of various wheels. For one, there are like...4 differnet diameters where there is a good qauntity of mass on wheels (when you see wheels with no tires on them, you know what i mean). Also, tire selection also has a large part as IT has the most extreme radius from the axis on which it is spinning....are you in Physics right now?

[franz]

Wheel manufacturers could calculate it for each wheel and tire manufacturers could calculate it for each tire, then you simply add them together. It wouldn't take them a machine any different than what I am typing on right now.

[bwanac]

Well true.

But to get a TRUE, reading use some kinda machine that spins them and shit. But if they did separates that could work. Guess, my brain is filled with senioritis and it does not want to work prperly.

[franz]

Well true.

But to get a TRUE, reading use some kinda machine that spins them and shit. But if they did separates that could work. Guess, my brain is filled with senioritis and it does not want to work prperly.

Reality and calculation would be VERY similar if the computer model is accurate, and I bet they have computer models already done for each in most cases, in fact I bet tire manufacturers already have the theoretical moment of inertia already calculated for most tires.

[rwh11385]

I first learned about I last year, but it was idling in this year's AP Physics when this came to mind.

Since Torque = I times alpha (rotational acceleration), the less the moment of inertia, the more accel.

And the weight (or mass) of the wheels is as important as where the mass is located. A smaller wheel has the mass closer to the center.

I don't think that it would be that hard either to calculate. Just a few integrals maybe. :P If they came out with moments for SSR Comps, Koseis, and various track tires run....that'd be interesting to see. :D

[rs4pro3]

Staticaly speaking finding the moment of inertia for a wheel would be easy, but when you get into dynamics it get's a little harder. I'm ending my second year now in Mechanical Engineering, and have done tons of Moment problems, and all you have to do is find it for both objects then add them together. All i've taken is Statics as we never even get into any Kinematics or anything that is moving(well except for shafts).

[rwh11385]

If this was more than just a quick pondering, I'd look into one of these random ME books lying around. (Dad went to Rose Hulman..... :? ) He was a ME.

Guess it's in the blood.

[Pedro]

(Dad went to Rose Hulman..... :? ) He was a ME. Guess it's in the blood.

So your dad is definatly no dummy and i would assume neither are you. when you get bored you should work on it, then try and use some time later in a class as a project or something

[rs4pro3]

If you have any Auto-cad software you can just draw the wheel, and have it calcuate Moment of inertia(i believe that was one of the things it calculates).
Most Static books have formula's for calculating Moment of inertia, but like I said they would just be for the object at rest.

[franz]

It's the same at rest or moving.
No books needed here, I am an ME and have passed the first part of the FE exam.
It's not a simple integral unless your wheel looks like a hockey puck, but a CAD program should be able to handle it that's why I think the manufacturers already have the data. Problem for the tire is there are different densities of material within the tire, also it deforms when mounted which would have to be taken into account.

[rs4pro3]

In that case for a wheel it self would be easy, but not for the tire

[Z3Jonathan]

As everyone mentioned, finding it wouldn't be hard if you had a solid model of the tire and wheel (with properties assigned to the different materials of the tire).

Creating a solid model of the wheel wouldn't be too terribly difficult. If its simple enough, you could probably make it from scratch, or get it off a coordinate measuring machine (CMM). Most modeling software (Pro/E, Unigraphics, Solidworks) should be able to give you a moment of inertia. AutoCAD, to the best of my knowledge cannot... And frankly, it would be a PITA to try and draw any halfway detailed wheel in AutoCAD. Most wheel of the decent wheel mfg's probably have this info, since many of them create solid models and do FEA analysis on them. Whether or not they will share this info, I don't know.

Creating a solid model of a tire would be incredibly complex. You've got various rubbers, steel and polymer cords, and internal carcases.

In short, you're time would be better spent trying to find light, strong wheels and tires, and leave it at that. Sure, you could get a "light" wheel and tire combo that has the mass towards the outer diameter, and a "heavy" wheel and tire combo that has more mass towards the inner diameter....

Jonathan

[rwh11385]

It's not a simple integral unless your wheel looks like a hockey puck

I never said it would be simple. I said it'd take a few ( :P = understandment) It'd be a royal bitch to figure for all the different materials in a tire.......

Jonathan is probably right, not worth worrying, but something I was pondering.