rec.autos.simulators

by **Joel Brow** » Wed, 23 Jun 2004 06:47:53

I'm designing a left front spindle for a 3100lb stock car (left turn only)
and would like to have some feedback if I'm on the right track as far as the
effect of the dynamic instant center. It's my understanding the dynamic
instant center should be above ground for the jacking effect to push the LF
corner of the chassis downwards. Your basic h / w =
cf(LateralWeightTransfer) should apply to the LF instant center from the
contact patch, is my understanding.

I have the LF instant center above the ground (in dive and roll) as much as
I can get without sacrificing my positive camber loss.

Any suggestions or comments are greatly appreciated.

by **J. Todd Wass** » Wed, 23 Jun 2004 07:46:00

Drawing a line from the LF contact patch through the LF instant center and then
measuring/calculating the angle between that line and the ground plane will
give an easy way to calculate the jacking force with acceptable accuracy. The
vertical (jacking) force in the ground's coordinate system should simply be:

Jacking_force = lateral_force * tangent(angle_between_ground_and_IC)

If the lateral force is acting towards the instant center, the jacking force
will be positive. In the LF wheel's case the force is pointing the other
direction (away from the IC), so the jacking force will be negative. It should
pull down on that corner of the car and reduce weight transfer at the front
axle, an oversteer effect in general. This assumes though that your suspension
is assymetical. I.e., of course if you raise the RF IC too it will dominate
and tend to produce oversteer.

Take care though since the IC may move significantly during body roll and the
only way I'm aware of to calculate the actual motion of the IC with acceptable
accuracy is through an iterative approach. I.e., software should help.

Todd Wasson
Racing Software
http://PerformanceSimulations.com
http://performancesimulations.com/scnshot4.htm

by **J. Todd Wass** » Wed, 23 Jun 2004 07:48:40

>Date: 6/21/2004 5:46 PM Central Daylight Time

>Drawing a line from the LF contact patch through the LF instant center and
>then
>measuring/calculating the angle between that line and the ground plane will
>give an easy way to calculate the jacking force with acceptable accuracy.
>The
>vertical (jacking) force in the ground's coordinate system should simply be:

>Jacking_force = lateral_force * tangent(angle_between_ground_and_IC)

>If the lateral force is acting towards the instant center, the jacking force
>will be positive. In the LF wheel's case the force is pointing the other
>direction (away from the IC), so the jacking force will be negative. It
>should
>pull down on that corner of the car and reduce weight transfer at the front
>axle, an oversteer effect in general. This assumes though that your
>suspension
>is assymetical. I.e., of course if you raise the RF IC too it will dominate
>and tend to produce oversteer.

Correction:
I.e., of course if you raise the RF IC too it will dominate and tend to produce
**understeer**.

Todd Wasson
Racing Software
http://PerformanceSimulations.com
http://performancesimulations.com/scnshot4.htm

by **Joel Brow** » Wed, 23 Jun 2004 11:22:04

Thanks Todd. I thought I was going in the right direction just wasn't quite
sure how to calc the LF jacking effect and if my understanding was correct.

> >Date: 6/21/2004 5:46 PM Central Daylight Time

> >Drawing a line from the LF contact patch through the LF instant center
and
> >then
> >measuring/calculating the angle between that line and the ground plane
will
> >give an easy way to calculate the jacking force with acceptable accuracy.
> >The
> >vertical (jacking) force in the ground's coordinate system should simply
be:

> >Jacking_force = lateral_force * tangent(angle_between_ground_and_IC)

> >If the lateral force is acting towards the instant center, the jacking
force
> >will be positive. In the LF wheel's case the force is pointing the other
> >direction (away from the IC), so the jacking force will be negative. It
> >should
> >pull down on that corner of the car and reduce weight transfer at the
front
> >axle, an oversteer effect in general. This assumes though that your
> >suspension
> >is assymetical. I.e., of course if you raise the RF IC too it will
dominate
> >and tend to produce oversteer.

> Correction:
> I.e., of course if you raise the RF IC too it will dominate and tend to
produce
> **understeer**.

> Todd Wasson
> Racing Software
> http://PerformanceSimulations.com
> http://performancesimulations.com/scnshot4.htm

rec.autos.simulators

*** Physics - Lateral Jacking Effects in SLA front suspension

*** Physics - Lateral Jacking Effects in SLA front suspension

*** Physics - Lateral Jacking Effects in SLA front suspension

*** Physics - Lateral Jacking Effects in SLA front suspension

*** Physics - Lateral Jacking Effects in SLA front suspension