## Moment of Inertia in a car.

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Sounds pretty much like the same thing as "response benefits" to me?
"Bernoulli is a nine-letter name"
xpensive

Joined: 22 Nov 2008

xpensive wrote:Sounds pretty much like the same thing as "response benefits" to me?

No - sorry, perhaps I didn't make it clear enough.

As I see it, with a low Polar MOI the object can be rotated around it's CofG with relative ease (starting and stopping the rotation is easier) - making a car that changes direction easily and responds quickly to inputs. As stated before this is a benefit all round (IMHO) until you reach the point where the driver gets in a muddle because he isn't sensitive enough and puts too much energy into the act of driving. At that point, giving the driver something he can control should be a better thing than something that is theoretically better.

What I mean is that as the car is turning and the tyre develops a slip angle, the intertia (is that the right word?) is greater, so the turning if the car is more likely to overcome the grip of the tyre.

As I said before - I don't know if this theory is utter rot - interested to find out from the guys who can do the maths
RH1300S

Joined: 6 Jun 2005

RH1300S wrote:
xpensive wrote:Sounds pretty much like the same thing as "response benefits" to me?

No - sorry, perhaps I didn't make it clear enough.

As I see it, with a low Polar MOI the object can be rotated around it's CofG with relative ease (starting and stopping the rotation is easier) - making a car that changes direction easily and responds quickly to inputs. As stated before this is a benefit all round (IMHO) until you reach the point where the driver gets in a muddle because he isn't sensitive enough and puts too much energy into the act of driving. At that point, giving the driver something he can control should be a better thing than something that is theoretically better.

What I mean is that as the car is turning and the tyre develops a slip angle, the intertia (is that the right word?) is greater, so the turning if the car is more likely to overcome the grip of the tyre.

As I said before - I don't know if this theory is utter rot - interested to find out from the guys who can do the maths

You can do the math all you like but until somebody drives it you just aint gonna know.
autogyro

Joined: 4 Oct 2009

Jersey Tom wrote:
autogyro wrote: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.

No Tom, now we know why three wheeled tadpoles are banned by the FIA
"You need great passion, because everything you do with great pleasure, you do well." -Juan Manuel Fangio

"I have no idols. I admire work, dedication and competence." -Ayrton Senna
Belatti

Joined: 10 Jul 2007
Location: Argentina

Belatti,

Sorry for all of the confusion. I should have just said yes, a lower MOI is always beneficial for handling.

But to quote Roark's (and correct some previous posters): The "first and second moments of inertia" are values that are established about an axis that is within the plane of area. The "polar moment of inertia" is a value that is established about an axis that is normal to the plane of area.

Reference: "Roark's Formulas for Stress and Strain, 6th edition, page 9 & 10"

Best regards,
Terry
"Q: How do you make a small fortune in racing?
riff_raff

Joined: 24 Dec 2004

riff_raff wrote:Belatti,

Sorry for all of the confusion. I should have just said yes, a lower MOI is always beneficial for handling.

But to quote Roark's (and correct some previous posters): The "first and second moments of inertia" are values that are established about an axis that is within the plane of area. The "polar moment of inertia" is a value that is established about an axis that is normal to the plane of area.

Reference: "Roark's Formulas for Stress and Strain, 6th edition, page 9 & 10"

Best regards,
Terry

Yep, so do the figures for a tadpole with non steering driven front wheels and a non braking variable caster rear steering wheel.
You might find it interesting.
autogyro

Joined: 4 Oct 2009

autogyro wrote:
riff_raff wrote:Belatti,

Sorry for all of the confusion. I should have just said yes, a lower MOI is always beneficial for handling.

But to quote Roark's (and correct some previous posters): The "first and second moments of inertia" are values that are established about an axis that is within the plane of area. The "polar moment of inertia" is a value that is established about an axis that is normal to the plane of area.

Reference: "Roark's Formulas for Stress and Strain, 6th edition, page 9 & 10"

Best regards,
Terry

Yep, so do the figures for a tadpole with non steering driven front wheels and a non braking variable caster rear steering wheel.
You might find it interesting.

Sorry, variable castor/camber rear wheel.
autogyro

Joined: 4 Oct 2009

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