Moment of Inertia in a car.

[Scotracer]

I assumed you mean Polar MOI as it's the only one relevant to a car on a very general level.

Yes, you want to keep PMOI to a minimum as it improves steering response and a car that reacts to inputs faster = WIN

[Shrek]

I know in a motor that you would like less MOI for the rotating weight(crankshaft, flywheel/torque converter, etc.) unless your mode of transportation loses a lot of speed when upshifting (i heard racing Chevy Corvairs at Bonneville salt flats had this problem)

[Caito]

I see how the center of percussion applies to a sword, or baseball bat. But how does it apply to a car?

What I mean is, both in racquet, sword, or bat you have someone holding one side, while the other is loose.

A car is in 4 wheels, and I cant find the analogy with the other items. Is there any one? The center of percussion is the point that, when a force is applied, would produce force cancellation and no net movement of one of the points. In a car of which point are we taking about, the front.. the back??

[xpensive]

Terry,

I was obviously talking about the polar mass moments of inertia. Arround the yaw (Z) axis to be precise. I name that "I" and to keep it simple -> M=I*ɤ (units Kg*m^2 in order to -> Nm = Kg*m^2 * 1/s^2)

Your teacher was correct B, however there still might be something missing here, let me try it this way;
As an analogy to F = m * a in linear motion, Moment equals Polar mass moment of inertia times angular accelleration in rotating, M = J * "phi dot-dot", where the latter has the unit of radians per second per second, or rad/s^2.

M = kg*m^2 * rad/s^2

[F1_eng]

Caito,

If the centre of percussion is a point where no net moment is produced if a force was applied to it, then it will also be the axis about which rotation occurs. In a car it will be the yaw rotation axis.

The position of this axis in relation to the vehicle determine how slip angles change during cornering, a relative forward position will incease slip angle during cornering and a rearward point will reduce angles.

Also, to a point the rear end of the car is fixed when it comes to latteral movement and the front is free to move, that could somewhat be related.

[Downforce]

What I mean is, both in racquet, sword, or bat you have someone holding one side, while the other is loose.

In a car of which point are we taking about, the front.. the back??

Tyre grip forces (lateral)?

At least that is how I imagine it...

[Belatti]

M = kg*m^2 * rad/s^2

Sorry, I used to write "rad" as a "1".
Also, in the "phi dot-dot", I wrote "gamma" but I guess some PCs may show it wrong.

[xpensive]

M = kg*m^2 * rad/s^2

Sorry, I used to write "rad" as a "1".
Also, in the "phi dot-dot", I wrote "gamma" but I guess some PCs may show it wrong.

When referring to angular speed in SI-units, "small-omega" is what is typically used. For angular accelleration, "omega-dot" or "Phi-dot-dot" will do. "Gamma" represents an angle if you ask me.

[bazanaius]

Belatti,


However, the term "moment of inertia" also can apply to structural member sectional properties. In regards to structural members, such as an F1 composite chassis tub in torsion or bending, having a higher structural moment of inertia would be very desirable. Since that would mean a more rigid chassis (remember basic Euler stress=Mc/I).

Best regards,
Terry

Do you not mean 'second moment of area'? The symbol (I) is the same, but I don't recall this being named 'moment of inertia'.

B

[xpensive]

Belatti,


However, the term "moment of inertia" also can apply to structural member sectional properties. In regards to structural members, such as an F1 composite chassis tub in torsion or bending, having a higher structural moment of inertia would be very desirable. Since that would mean a more rigid chassis (remember basic Euler stress=Mc/I).

Best regards,
Terry

Do you not mean 'second moment of area'? The symbol (I) is the same, but I don't recall this being named 'moment of inertia'. B

Perhaps Terry is confusing, Moment of Inertia (I) which relates to deflection (delta), with Bending Resistance (W) relating to stress (sigma)?

[PlatinumZealot]

To me:

Moment of inertia is when it is about a an axis parallel to the frame that you are viewing.

Polar moment of inertia is when it is about a perpendicular axis to that frame you are viewing. Or the inline with whatever rotation axis.

That is how i remember it.

You usually use J when you are dealing with torsion in a load bearing structure, like a drive shaft.

[xpensive]

Perhaps we have a bit of a misunderstanding here?

Surface moment of inertia (I) is the stiffness of a cross-section subjected to a bending moment (M) resulting in deflection (delta).

Mass moment of inertia (J), is the angular equivalent of mass in linear accelleration (F = m * a), as M = J * angular accelleration.

Two completely different entities.

[autogyro]

F1 eng

Is all this, why a three wheeled tadpole with FWD, no steering at the front and positive variable rear wheel camber, is better at road holding than any four wheeled vehicle?
Something to do with vertical and horizontal centers?

[Jersey Tom]

F1 eng

Is all this, why a three wheeled tadpole with FWD, no steering at the front and positive variable rear wheel camber, is better at road holding than any four wheeled vehicle?

Uhh.. says who.

[RH1300S]

Somewhere in my befuddled and not very technical brain is an itch.

I am fairly sure I have read that in addition to the response benefits that a low polar moment of intertia gives, there is also a benefit in improved tyre grip from having a reduced torque around the CofG.

Sensible or confused rubbish???