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Thread: Passive rear steer revisited Reply to Thread
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Topic Review (Newest First)
06-13-2007 07:49 AM
Buickboy I just have to say it, threads like these are why I love FF.com!
06-13-2007 06:37 AM
KillaLude
Quote:
Originally Posted by Carrera26 View Post
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
06-12-2007 04:44 PM
thenorm
Quote:
Originally Posted by S1lkwrm View Post
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
06-05-2007 02:51 PM
Carrera26 And then, from the cold heart of the grave itself, the thread rose from the dead to haunt the board once again....
06-04-2007 10:12 PM
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.
11-18-2005 09:07 AM
Carrera26 passive rear steering. A suspension system that actually turns the rear wheels due to changes in suspension geometry (like compression).

ars = active rear steering. A suspension system that turns the rear wheels by active computer or mechanical control.
11-18-2005 08:36 AM
Torche wow.

you guys just made me realize how little i actually know about car mechanics.


second off.

prs??
11-17-2005 11:16 AM
Carrera26 As one side compresses, with the Control Blade, it toes out just a bit, I believe. If you are compressing one side, then you are taking weight off the other, which would have the opposite effect, which would be toe-in. This would get both of them pointing in the same direction, which helps quell understeer. (Don't know a ton about Control Blade, anyone with facts that contradict please post)

Your looking at this process a little later than you need to. By that I mean that it's what the tires are doing before it compresses that makes the most difference. There's a split-second lag between the initiation of the turn and when the car settles to it's max roll level. Static toe-out (I actually reccomend 0 toe in the rear, stock they have toe-in) will be what controls the process at initiation, which really has a lot more effect.

Especially in quick transitions, like in a slalom, the car will only lean a bit in one direction before you have it headed back the other way. The fast line is the one that for the most part has the least actual cornering Gs possible, as in it's the straightest and most flowing line. There are very few situations on the street, road course, or especially the AutoX course when you are going to be sitting their at max roll, at least if you are doing it right. Unless I am in a "carousel", which is a situation for me to induce rear slip and rotation by weight transfer or steering input anyway, not to sit there through a static G load.

So in every situation outside of long and constant radius sweepers, when you are driving right, you're not going to use much dynamic toe change anyway.
11-16-2005 08:37 PM
S1lkwrm
Quote:
Originally posted by Carrera26
There is a simple, cheap, and effective way. In fact there are several. Just changing the static toe, rear-sway, damper settings, camber, etc. will all adjust that. Not only can you fine-tune the attitude of the car, but it's consistent and predictable, instead of trying to tune a dynamic system like PRS. As I said, it's a lot easier and effective to make a change that is consistent and then adapt your driving to suit it...

The piece of metal you are talking about is the "Control Blade", btw.
Im learning here so bare with me..

If I were to adjust the static toe(out) evenly on both sides wont that cause one wheel to track and the other (inside) wheel to go against it thats the only thing that bugs me about a static toe change. well except toe in to make more stability in braking. Hmm actually as Im typing this i just hought about what you said its basicly going to cause the out side wheel to toe out more but the inside will toe in to track as well but just not as much as the rear since the static change was made. ok my brain hurts now.
11-16-2005 02:10 PM
Egz All i know is I'm happy how mine is on the track as it is.
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