Pelican Parts
Parts Catalog Accessories Catalog How To Articles Tech Forums
Call Pelican Parts at 888-280-7799
Shopping Cart Cart | Project List | Order Status | Help



Go Back   Pelican Parts Forums > Porsche Forums > Porsche 911 Technical Forum


Reply
 
LinkBack Thread Tools Rate Thread
Author
Thread Post New Thread    Reply
jyl jyl is offline
Registered User
 
jyl's Avatar
 
Join Date: Jan 2002
Location: Nor California & Pac NW
Posts: 20,182
Garage
Eccentric Spring Plate Bearings?

So I was thinking about a modification to the 911 rear suspension spring plate.

The concept would be to make the bushings or better yet the polybronze bearings eccentric.

So that when the rear supension is loaded (pivots up), the spring plate moves forward, causing additional toe-in at the rear wheel.

So suppose the 911 is initially set up with neither toe-in nor toe-out at the rear wheels (neutral toe). When the 911 is in a hard right turn, the left rear suspension is loaded, and the left rear wheel moves to toe-in, which causes the rear tire to steer "into the turn". The right rear suspension is unloaded, and the right rear wheel moves to toe-out, and it too steers into the turn. When the 911 is on a straight-away, the rear tires revert to neutral toe.

Any reactions? Would this work, or is it another "tapered torsion bar" (a superficially interesting idea that wouldn't in fact work).

Oh, by the way, my first idea was to make the trailing arm to torsion bar tube bushing (or monoball) eccentric. But considering the small diameter inside the trailing arm end, and that a spherical bearing already has to fit in there, it seemed too hard to add eccentricity to that mechanism.

__________________
1989 3.2 Carrera coupe
1988 Westy Vanagon, Zetec conversion
Really want to find a clean E28 . . .

Last edited by jyl; 01-02-2004 at 04:33 PM..
Old 01-02-2004, 04:28 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #1 (permalink)
Registered User
 
Chuck Moreland's Avatar
 
Join Date: Apr 2002
Location: Santa Clara, CA
Posts: 5,665
The 911 does toe in a bit in the rear when the suspension is compressed. This actually contributes to the lift-throttle-oversteer problem, when you back off the throttle the car toes out.

I'm not sure that increasing this tendency is a good thing.

Perhaps an eccentric to cancel the factory toe in tendency, reducing lift-throttle-oversteer?

20 years ago (am I really that old) 4 wheel steering was all the rage and was supposed to be the next big thing for sports cars. In general those efforts weren't very succesfull. Does anyone remember that was the big sales pitch for the gen 2 RX7? It didn't work very well so they quit talkng about it.
__________________
Chuck Moreland - elephantracing.com - vonnen.com
Old 01-02-2004, 04:41 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #2 (permalink)
jyl jyl is offline
Registered User
 
jyl's Avatar
 
Join Date: Jan 2002
Location: Nor California & Pac NW
Posts: 20,182
Garage
Wasn't the multi-link rear suspension for the 993 designed to toe-in when loaded? I read about it, I can't recall the details but all those unequal length struts must be designed to make some dynamic change to the geometry.

Anyway, you think it would be better to have the eccentric create more toe-in when the suspension is unloaded? (Or maybe it would be better to forget about the eccentric feature entirely).
__________________
1989 3.2 Carrera coupe
1988 Westy Vanagon, Zetec conversion
Really want to find a clean E28 . . .
Old 01-02-2004, 04:56 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #3 (permalink)
Registered User
 
Join Date: Oct 2003
Location: London Ont Canada
Posts: 3,107
Wouldn't the result be better known as "bump steer" ? Certainly a little toe in on droop would be nice to have to help keep control if landing after being airborn .However toe change with suspension movement will usually steer the vehicle without the predictable result like you get with a steering wheel.I see 4 wheel steer is back now on some of the GM pick ups but more for parking ease not handling improvements.
__________________
1980 911 SC 3.6 coupe sold
1995 993 coupe
1966 Mustang Shelby clone
1964 Corvair Spyder Turbo gone
2012 Boss 302
Old 01-02-2004, 05:40 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #4 (permalink)
jyl jyl is offline
Registered User
 
jyl's Avatar
 
Join Date: Jan 2002
Location: Nor California & Pac NW
Posts: 20,182
Garage
Hmm, I just did a little reading on different Porsche rear suspensions.

Apparently Porsche started working on so-called "passive steering" or "toe control" in the 70s with the 928's "Weissach" rear suspension, a modified semi-trailing arm designed to create toe-in under braking.
The 993's and 996's multi-link rear suspension is also frequently referred to as having "Weissach" "toe correcting" or "toe control" characteristics. I don't know how the 993 / 996 designs work. But it seems clear that the various "Weissach" designs from 928 to 996 respond to the rear wheel being pulled backwards relative to the car (as would occur under braking), not to the rear suspension being loaded or unloaded.

Well, the eccentric spring plate bearing idea would respond to loading and unloading, so I guess johnsjmc is right to call it "bump steer".
__________________
1989 3.2 Carrera coupe
1988 Westy Vanagon, Zetec conversion
Really want to find a clean E28 . . .
Old 01-02-2004, 09:59 PM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #5 (permalink)
Registered User
 
davidl's Avatar
 
Join Date: Nov 2001
Posts: 100
Hello there.

I think there is a fundamental mistake in the proposal.

It is not at all simple to design any bearing which will alter its intantaneous point of pivot .

What mechanism did you have in mind?

( Neglecting for the time being any discussion as to whether this is desirable).

kind regards
David
Old 01-03-2004, 05:59 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #6 (permalink)
 
Registered User
 
Join Date: Oct 2003
Location: London Ont Canada
Posts: 3,107
The key to good vs mediocre handling is predictable paths that the wheels follow while moving up and down ,loading and unloading,side force and thrust. All independant suspensions are set up with varying amounts of static toe ,either in or out ,usually in to counter act their natural tendancy to toe the other way under power .Movement fore and aft could be done with voided bushings but sport minded drivers usually use stiffer bushings to limit the movement and as a result improve the predictable character of their ride.

__________________
1980 911 SC 3.6 coupe sold
1995 993 coupe
1966 Mustang Shelby clone
1964 Corvair Spyder Turbo gone
2012 Boss 302
Old 01-03-2004, 08:05 AM
  Pelican Parts Catalog | Tech Articles | Promos & Specials    Reply With Quote #7 (permalink)
Reply

Thread Tools
Rate This Thread
Rate This Thread:

 


All times are GMT -8. The time now is 08:01 AM.


 
Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2020, vBulletin Solutions, Inc.
Search Engine Optimization by vBSEO 3.6.0
Copyright 2020 Pelican Parts, LLC - Posts may be archived for display on the Pelican Parts Website -    DMCA Registered Agent Contact Page
 

DTO Garage Plus vBulletin Plugins by Drive Thru Online, Inc.