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

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.

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

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>From: [email hidden] (J. Todd Wasson) >Date: 6/21/2004 5:46 PM Central Daylight Time >Message-id: <[email hidden]> > >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

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. "J. Todd Wasson" <[email hidden]> wrote in message news:[email hidden]... > >From: [email hidden] (J. Todd Wasson) > >Date: 6/21/2004 5:46 PM Central Daylight Time > >Message-id: <[email hidden]> > > > >Drawing a line from the LF contact patch through the LF instant centerand > >then > >measuring/calculating the angle between that line and the ground planewill > >give an easy way to calculate the jacking force with acceptable accuracy. > >The > >vertical (jacking) force in the ground's coordinate system should simplybe: > > > >Jacking_force = lateral_force * tangent(angle_between_ground_and_IC) > > > >If the lateral force is acting towards the instant center, the jackingforce > >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 thefront > >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 willdominate > >and tend to produce oversteer. > > > > Correction: > I.e., of course if you raise the RF IC too it will dominate and tend toproduce

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