Radius of gyration 3

[BorisShakhov]

Good day.

Is there any simple method to approximate a radius of gyration of a car?

I have found on a recent thread the next statement:
useful term that represents the departure from one (1.00) of the yaw radius of gyration [in meters]

Can someone explain more what does it mean 1.00 in relation with CoG?

I`am trying to make front heavy Audi RS2 Avant Quattro with I5 engine be more agile.
Is it right in a real world trying to tune response on a production wagon by playing with PMOI and weight?

Chassis of the subject

P.S. Sorry for the grammar, English isn't my native language.

 

[GregLocock]

Well that's easy, tires and throw the rubbish out of the car. Then play with tire pressure.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[gruntguru]

"Another thing that I want to try is to increase front dampers low speed compression force. Main idea that it will increase lateral force on the fornt outer wheel so yaw will build up quicker.
Can it help in my situation? Or there is a mistake in understanding?"

That will probably reduce agility by increasing front weight transfer on turn-in. If the car is not already picking up the inside rear, you may be able to improve turn-in by doing the opposite - increasing rear damping.



je suis charlie

 

[JayMaechtlen]

This may be a dumb question, but:
Generally, when the car turns, where's the center of rotation?
Would it (ever?) be at the CG? (unless all four tires are sliding)
Without significant rear steering, wouldn't it usually be somewhere near the center of the rear axle?
Then the important MOI for each component would be its mass and its distance from the real center of rotation to the CG of that component, wouldn't it?
regards
Jay

Jay Maechtlen

http://www.laserpubs.com/techcomm

 

[GregLocock]

The instantaneous center of rotation is at the intersection of the perpendiculars to the velocity vector at each axle, ie somewhere a long way from the car.

That's pretty funny and fundamental, need to have a think about that.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[gruntguru]

When its going in a straight line the axis of rotation is a long way of to the side from the car(infinity in fact)and and moves in closer as you turn tighter.

je suis charlie

 

[Panther140]

Relocate battery to the trunk if you haven't already. Some of those euro cars are coming with them already mounted in the trunk now, like my volvo S60 T5 that I had. It was a complete electro mechanical blunder of an automobile, but they got a few simple things right.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[gruntguru]

Moving the battery to the boot will be great for F-R weight distribution, but will probably be further from CG (on this front-heavy car) and thus increase MOI.

de ja vu all over again

je suis charlie

 

[Panther140]

If you really want lower MOI, do this!

https://www.youtube.com/watch?v=UfpQTAFoTU4

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[Tmoose]

"

https://www.youtube.com/watch?v=UfpQTAFoTU4

"

Does the "too light to hook up " at ~ 4;50 really make sense?

I'm guessing the front/rear weight bias may be pretty bad possibly worsened by rear roll stiffness, or the max camber adjustment is now insufficient, or soomething.

 

[Overrun]

If your issue is mostly turn-in, check tire temps to see if they’re pushing or not hooking up. Either Ackerman or anti-Ackerman –the latter is theoretically preferable- can help as well as relative lower front roll stiffness. Torque vectoring would really help but I have no idea as to its availability in your case.

In my opinion you’d be much better rewarded to work on dial in variables before resorting to the heroics you’re considering.

 

[dynatune4xl]

If I take the average in my database of all cars that I have had measured the average radius of giration of a car turns out to be 45% of it's wheelbase. Note however that the "extremes" go from 40% to 50%.

Cheers

dynatune4xl