914 ride height?/raising rear/trailing arm ideas? Options

[slugmika]

I'am going to raise my rear suspension pick up points and would like to know what should be the ride height?
I found that front shoud be 108mm from torsion bar center to spindle center.
What is Porsches recomendation?
I know that some of you have raised pick up points, have you used the factorys specs or what.
How much have you raised those?

And finally, is there any poin to make the stock kind of trailing arms? I have allready made a jig with stock trailing arm dimensions. Those would use stock bearing hub but otherwise made of tube. We would use uniball's rather than stock kind of bushings.

Car is now on a table and it would be easy to make allmost anything, so if you have good ideas feel free to share

Thanks
Mika

[IronHillRestorations]

Check out Chris Foley Welding. He's come up with just what you are asking about. Not new trailing arms, but raising the rear suspension mounting points.

[Mueller]

i don't think that the raising of the rear pick up points was ever done by the factory, but I could be wrong

it seems most are raised in the 1.5" to 2"+ range.

The goal is to have the trailing arm parallel to the ground
(the axis for the pivot point and axis for the wheel bearing to be equal distance from the ground)

on thing you could do (seach for Brents vintage racer build up) is turn the trailing arm into a "true" trailing arm instead of a semi-trailing arm which it currently is (camber changes with the movement of the suspension)

This post has been edited by Mueller: Oct 6 2005, 12:00 PM

[slugmika]

Yes i know factory didn't raise the pick up points in 914 but i think it would be wise to maintaint the original geomethry.
"(the axis for the pivot point and axis for the wheel bearing to be equal distance from the ground)"
-i would like to know what is the factorys instructions according to pivot point axis to wheel bearing axis. I think it has to be higher in a pivot point side in a static situation but how much ?
i'll try to find that Brents topic

thanks

Mika

[groot]

Warning... I'm opinionated on this subject....

Check your toe and camber change with each starting angle on your trailing arm. It will make it very obvious what the real solution is.

IMO a trailing arm is not better than a 12.5 degree semi-trailing arm... you want some camber gain with roll/jounce.

I can tell you what I think, but it's better if you know and understand the dynamics for yourself...... hint... toe out in jounce is not a good thing.

[Mueller]

QUOTE (groot @ Oct 5 2005, 10:46 AM)

Warning... I'm opinionated on this subject.... Check your toe and camber change with each starting angle on your trailing arm. It will make it very obvious what the real solution is. IMO a trailing arm is not better than a 12.5 degree semi-trailing arm... you want some camber gain with roll/jounce. I can tell you what I think, but it's better if you know and understand the dynamics for yourself...... hint... toe out in jounce is not a good thing.

I'm still a newbie myself with this suspension stuff (IMG:http://www.914world.com/bbs2/html/emoticons/wacko.gif)

So with the limited range of motion for most car setups, is there not a concern of too much camber due the movement at an extreme roll or compression of the suspension?

[groot]

Mike,

You're correct... but zero camber gain is bad, too. So, you should have at least enough camber gain to offset the roll angle of the vehicle and depending upon what tires you use, you probably want more camber gain than that...

Think of it this way... if your car rolls 2 degrees and your static camber was -1 degree, what it your camber when your in a roll condition? Ideally, you'd want your roll condition to introduce additional camber, but not too much. Many times static alignment is set to get your roll camber correct (for extreme examples look at fwd touring cars), but if you have appropriate camber gain, you can run less static camber.

[Mueller]

QUOTE (groot @ Oct 5 2005, 11:55 AM)

Mike, You're correct... but zero camber gain is bad, too. So, you should have at least enough camber gain to offset the roll angle of the vehicle and depending upon what tires you use, you probably want more camber gain than that... Think of it this way... if your car rolls 2 degrees and your static camber was -1 degree, what it your camber when your in a roll condition? Ideally, you'd want your roll condition to introduce additional camber, but not too much. Many times static alignment is set to get your roll camber correct (for extreme examples look at fwd touring cars), but if you have appropriate camber gain, you can run less static camber.

thanks for the explanation...I was thinking pretty much in just one dimension (going straight and compressing the suspension)...

actually, it was even less so, I was mostly thinking of the swinging action while the car is static....gotta learn how to read and buy some books (IMG:http://www.914world.com/bbs2/html/emoticons/clap.gif)

[slugmika]

Warning... I'm opinionated on this subject....
-Ok i'am warned (IMG:http://www.914world.com/bbs2/html/emoticons/wink.gif) I'we noticed that you seem to have one fast 914 so i'am listening.

Check your toe and camber change with each starting angle on your trailing arm. It will make it very obvious what the real solution is.
-It seems that now when my car is lowered to desired height, i can't have any toe in in rear. Trailing arm's might have bended but i'am not sure. Because i'am not an engineer, i was wondering that maybe it would be wise to keep the original geomethry in there? Only raise the pick up point's?

IMO a trailing arm is not better than a 12.5 degree semi-trailing arm... you want some camber gain with roll/jounce.

I can tell you what I think, but it's better if you know and understand the dynamics for yourself...... hint... toe out in jounce is not a good thing.
-My main idea to raise the rear is to correct the extreme trailing arm angle. I have severe traction problems in rear and that trailing arm angle and toe out must be main issues?

Thanks

Mika

[groot]

Mika... you're asking the right questions and don't worry about not being an engineer, it's only a geometry issue.

While your static toe may be zero, what happens when that wheel goes into jounce? That's what's important... the toe change with suspension movement.

I have never talked to any of the original 914 suspension engineers, but my best guess for their original setup is this...

I think they set up the rear trailing arm for toe out in jounce to produce roll oversteer to correct for the horrible front geometry, which has roll understeer. So, returning the arm to its original angle may not be in your best interest. This car does not need anymore oversteer.

The original setup may have been okay for production, but we change many things on these cars and the original "balance" of spring/damper rates and stabilizer bars is long gone.

But, don't take my word for it.... you've got your car on a plate. Measure the toe at below ride height, then raise it 1/4" and measure the toe, repeat until you've reached full jounce. Plot the toe change and determine your ideal starting angle of the trailing arm by tring to minimize toe change over your travel.... it won't be zero and a little toe-in gain is preferred over any toe-out gain.

[slugmika]

Ok thanks
I'll start measuring my car next weekend.
I may have to steal some ideas from that BMW site (IMG:http://www.914world.com/bbs2/html/emoticons/smile.gif)

Terveisin
Mika