Coilovers plus springplate question...

[Kemo]

Here is a pic i ganked from the Patrick Motorsports site. I think the owner of this fine automobile is a poster here on the BBS. In any event, I have a question concerning the springplate combined with coilovers.



For some reason I thought the springplate was no longer needed when going to coilovers. There must be some function that the plate serves in this setup. As usual, I'm hoping to be educated

Thanks for the comments...

[aus911]

Kemo
Depending on the conversion you can have "coil assisted" which you retain the torsion bars and standard spring plates, or, in a complete coil over conversion the torsion bars are no longer used but you still have to locate the banana arms, in this case it looks like a rose joint has been joined to a standard looking spring plate, no torsion bars and coil overs.

Hope this helps
Ray

[Kemo]

Ray,

Thanks for the input. So it seems that the spring plate is not really providing any spring but is still used to kinda line things up? I see alot of bolts and stuff up there where the torsion bar cover "used" to be. So is the Rose Joint all of that? Im not sure what a Rose Joint is.

Thanks for the help,

[ChrisBennet]

Without a spring plate of some sort, there would be nothing to keep the wheel from moving towards the back of the car. The spring plate forms one side of a triangle - the car body and the control arm (aka "banana arm") form the other 2 sides.

When using coil overs you don't necessarily need the torsion bars or the factory spring plates which use the torsion bars to support the car. However, you still need some sort of spring plate to control the location of the wheel - like the 935 style spring plates in the picture.
-Chris

[aus911]

Kemo,
This is a pic of a rose joint, the rest is the standard mount hardware that has been modified to support the rose joint

[ChrisBennet]

Here's a picture of a 935 style spring plate from Autometric's web site: (http://www.autometricsmotorsports.com/images/cars/ron/ron_935_rr_arm.jpg)



aus911: I don't believe that the spring plate on the Patrick Motorsports car is a "standard mount hardware that has been modified to support the rose joint". It looks like one of the aftermarket 935 style spring plates.
-Chris

[aus911]

Chris,
Relax, I was just trying to simplify things to explain what Kemo was looking at, the theory is the same!

Cheers
Ray

[Kemo]

Thanks for the info guys.

From all this, I'm assuming that the 935 style spring plate is used to stop the banana arm from swinging from front to rear. AND, this spring plate is adjustable, im assuming to help align the wheel easier with the rose joint as opposed to big bolts closer to the wheel.

Next question... Can a stock spring plate with no torsion bar be used to accomplish the same thing? Seems like once you got the wheel straight you wouldn't really need to adjust the front to rear position that much. How much strain is placed on the mounting area at the torsion bar cover? seems like it would be minimal and shearing.

Thanks,

[aus911]

Kemo,
I have never seen it done, but I don't see why not, I am sure someone else has tried this and will chime in

Cheers
Ray

[911ctS]

Next question... Can a stock spring plate with no torsion bar be used to accomplish the same thing? Seems like once you got the wheel straight you wouldn't really need to adjust the front to rear position that much. How much strain is placed on the mounting area at the torsion bar cover? seems like it would be minimal and shearing.

Yes, a stock spring plate can be used without T-bars and essentially accomplish the same thing. The 935 style spring plates make camber and toe adjustments much easier as well as eliminate the need for spring plate bushings since the heim joint, rose joint, or rod end (we all call it something different) does this.

I have seen quite a few RSR's that run coil overs but still retain the stock front and rear suspension arms and spring plates.

[911pcars]

Rose joint. Haven't seen that term for awhile.

Also commonly called:
Rod End
Heim joint


Sherwood

[Walt Fricke]

Right - my race car ('68 912 Targa base tub) came that way: converted to coilovers, but with Delrin bushings in the torsion tube and stock spring plates. Worked fine.

But who would not want to imitate a factory race setup? And it is easy: drill and tap a slug which you weld into the end of the torsion tube. Fabricate a new 4 bolt cover so you keep the big through bolt in double shear. Cut an old spring plate up and weld on what amounts to a nut. Screw a Heim (German name, British is Rose, and we tend to use "rod end" or "spherical bearing" here if we don't use Heim, but all the same - though spherical bearing is generic and also applies to the bearing part itself) in, and you are set. Well, while at it you may want to make a fancier setup so you can adjust the Heim without having to disconnect anything, and so on. Plus you can provide a higher mounting - see the nice Autometrics picture showing two mounting holes. This is very helpful with a lowered car.

Anyway, from my lights anyone who is going to the trouble of switching to coilovers really ought to go to a Heimed spring plate as well. This is all pure racing stuff.

Kemo - I think maybe the term "spring plate" is what had you confused (though if you just jack up your car and stick your head in there and look at the rear suspension you will quickly see how things won't work at all without something in there doing that plate's job, or at least one of its jobs).

I have always figured that the term arose not from its function, with a torson bar suspension, of acting as a lever arm for the spring (torsion bar), but because it is flexible (springy) in the sideways direction. The way it is mounted makes it want to go up and down only in a single plane. That plane is not necessarily perfectly lined up with the plane (or planes) the wheel has to travel given the rest of the suspension. But the flex of the plate allows for this.

When you switch to coilovers and a spherical bearing the plate no longer needs to be springy, since the bearing allows things to move to keep lined up.

Walt Fricke

[SoCal70RSR]

Not to stray to far off the subject... Anyone out there who's done the upgrade to the 935 type spring plates and coil-overs could tell us the difference in handling, noise, good/bad? Is it advisable for a street car? How about a 50/50 track and street car?

[MarKoBrow]

To add to SoCal's question what spring rates are advised front and rear for a car that is driven on the street? Or better stated is there a conversion rate for torsion bars ?

[mb911]

at some point I am going to go to the coil overs in the rear to help my weak t-bars. and maybe eliminet them at all .. rebelracing has a very inexpensive kit that should answer allot of questions

[Walt Fricke]

I don't think coilovers are very sensible for a street (or even a street/track) car. Extra expense, have to reinforce things. And the ride with 23/33mm T bars is certainly as stiff as you would want on the street. Well set up torsion bar sprung cars are plenty fun and fast on the track, at least with stock engines (as in racing).

Because springs are relatively easy to change, a guy might think that he'd toss on the 400/600 lb springs for the track, and go back to 200/300s or something like that for the street. I used to think I'd reset my sway bars after each track event, maybe swap brake pads back and forth. Suuure. I learned to live with it.

Plus you'd have to reset the ride height (which, in fact, is fairly easy to do with coilovers) so your pan wouldn't be dragging with the softer street springs. Which would mean resetting the toe, which is a bit of a pain if you think of doing it on a routine basis.

Steve Timmins' website (what he calls his Porsche hot rod sideline escapes me for the moment, but you can find it easily enough) has a chart comparing various torsion bar sizes, front and rear, with equivalent coil spring rates. You will be surprised at what you see (at least I was).

Walt Fricke

[Wil Ferch]

I also published a spring rate chart which (humbly) I think is more accurate. It was first published as a Rennlist article but has been reposted here several times.

Caveats:
- these are "equivalent wheel rates"..and not pure spring rates, if you see the nuance. That is..it describes the "installed" condition as seen by the wheels.
- as accurate as I believe the chart to be..the fronts will "in actuality" be a bit softer than stated, because of the construction method used. In essence, the torsion bar nests inside the longitudinal member of the lower A-arm...with one end of the bar "fixed" at the front suspension pivot..and the rear-most portion connected ( if you will) at the "lever arm" , or the portion of the A-arm that transmiits forces from the wheel. When you study this arrangement, it becomes obvious that the "nesting" of the bar is only a packaging convenience, and the effective length of the longitudinal member is "longer"... and the surrounding support tube ( that surrounds the torsion bar and is part of the A-arm)... itself "twists" with a torsional rate all its own. All this conspires to get an effective wheel rate slightly softer than my list suggests.

http://tech.rennlist.com/911/pdf/torsionbars.PDF


Kinda hard to describe w/o pics...but some should get the picture of what I'm trying to say.

BTW...it shouldn't be "too" surprising about the spring rates...the rate is a function of the torsion bar diameter raised to the FOURTH power. So...a small increase in diameter will result in a large change.

- Wil