Passive rear steer revisited

[WeeAsp]

To echo earlier comments, lose the PRS. The only real benefit to the system is parallel parking...

IN AX and track situations, much like traction control, the system is engaged to be smarter than you are. This is rarely the case as your instincts are to over correct.

To further add to Carrera and Geezer's comments, for our cars, the optimum set up is for the rear toe to be at 0 or a slight negative to further facilitate turn in. Toe out can create exciting times under extreme cornering.

For more on vehicle dynamics check out:

http://www.miata.net/sport/Physics/

The Physics of Racing.

[Carrera26]

And then, from the cold heart of the grave itself, the thread rose from the dead to haunt the board once again....

[thenorm]

Originally Posted by S1lkwrm

Assumptions:

- turn left and the suspension rolls right and rear right tire toes out and I think rear left toes in causing the rear steer.

umm, isnt this backwards? when u compress the suspension, the tires toe in. This has the effect of lessening the yaw (rotation) induced by sudden steering imput.
The suspension is designed so that Joe Shmoe, when he panic turns around a dog that runs into the road, doesnt loop it into a telephone pole. It was not designed to improve turn in for racing. It is an economy commuter car afterall.

If you look at the control arms of the rear suspension, you'll see that the control arm towards the front is short than the rear, when the suspension compresses it has a shorter arc and it esentially pulls its part of the "blade" trailing arm towards the middle of the car. this flex of the control blade is what toes the tire in on suspension compression.

That why after I lowered my car, my rear toe visibly pointing in.

to modify the PRS, you would need to change the starting position of the front control arm. If it started out aimed downwards instead of horizontal, the inital swing of the arc would push the control blade out (causing toe out), then as it passed horizontal would pull the blade back in (toe in).
if that makes sense to anyone else


umm ya, jsut noticed this was a dead thread that i was responding too, but too late now. this info is still important

[KillaLude]

Originally Posted by Carrera26

Other cars with rear steer

Porsche 928
Nissan 300ZX, Skyline, Micra
Honda Prelude SH
Mazda RX-7 (FC3S), MX-6
SAAB 9-3 (ReAxs Equipped)
VW Corrado
2006 G35, M45
Rolls Royce Phantom
Several non-us cars (EDM, JDM, ROW cars)
Toyota Aristo (Lexus GS here I believe, not equipped so in US)
GM trucks (QuadraSteer)

And probably many others. Even the Focus's Control Blade suspension offers a bit of passive rear-steer.

the prelude SH had ATTS active torque transfer system in the front of the car, the late 80s early 90s preludes had the 4WS system

[Buickboy]

I just have to say it, threads like these are why I love FF.com!