So I'm already hemoraging money all over the suspension bits of my car. Why stop the bleeding so soon when there are so many parts to buy...

When the car goes back together I'm lowering it as far as practical for an AX/street ride (my driveway may be the ultimate constraint). I've already experienced the near complete elimination of bump steer by installing washers under the steering rack so I never want to put up with bump steer again. So I'm looking at my options and see two. The first is to install a ERP bump steer kit (hit page down a couple of times to find it) so I can dial out the bump steer no matter where the ride height is set. The second option is to go to the Tangerine racing raised strut spindleswhich appear, looking at the digipic, to have the control arm bent to a corrected position to eliminate bump steer while resetting the ride height via the relocated spindle. I suppose the raised spindle also has the advantage of not using any of your suspension travel to achieve the lower chassis height.

Whata ya think? The price is a wash. Anybody done both or one or the other to provide and comparison/comments? Oh this all assumes that the dreaded bump steer will show up with a vengance as I crank the car lower...

Thanks,
Kevin

I think these two things serve different purposes -- the bump steer kit allows fine-tuning to negate bump steer effects on the front end geometry, whereas the raised strut spindles allow you to get back some suspension/shock travel when lowering the front end significantly (I think 17-21mm is a typical range of travel recovered).

I will most likely be doing both mods this summer and of course will take pics and report any findings (good or bad).

Without raising the spindles there are two limitations other than bump steer to how low you can go. Both affect cornering limits. The first is bottoming the shock, which will cause a sudden increase in spring rate and potential loss of control, and could damage the shock if bump rubbers aren't installed. The second is that the camber change is altered when the a-arm is angled upward. This adversely affects the tire contact patch.
Raising the spindles improves both of these conditions.

Yes, when I raise the spindles I also re-curve the steering arm so the tie rod end is in the same relationship to the steering rack as before. This has the added benefit of slightly increasing the steering rate, due to the effective length of the steering arm being shortened.

The raised strut is the hot ticket... BUT..BUT.. if your thinking about 5 lug later I wouldnt do it. Hold off until you convert the car (I dont recall if your car is already 5 lug or not).

The ERP/Smart bumpsteer kit awesome. It really lets you fine tune the bump for your car.

B

I'm a 4 lug guy. I don't have any plans to go 5 with this car.

I think what I'm gonna do is put 'er back together and set the ride height were it's going to be, check the bump steer and talk to Chris about the raised spindle position (It'd be pretty cool if he does custom spindle positions). I really like the idea of having full strut travel AND lower ride height.

Thanks!
Kevin

He can do it (as well as others) Its a lot of work to raise a 4 lug strut.

B

How is the 4 lug strut different than a 5 lug for the purpose of raising the spindle?

Or, why is it more difficult?

You cant raise the spindle on a 4cyl strut or a early 5 lug strut. The strut is tapered.

SC/Carrera/Bilstein/Koni/Boge are not tapered and the spindle can be raised without "major" hassle like the 914 strut.

You have to cut the strut in two places... instead of just moving the spindle up.

B

Whatever he adds to the bottom (raise spindle) has to be removed from the top yet still retain your threaded collar "threads".


B

Nice Berber carpet Chris...LOL


B

Got it. Now that I've asked the question I vaguely recall a similar thread not too long ago.

That's the left over from doing my sister in law's condo. It covers the stained carpet in my basement office until we install new stuff here.

I can set the spindle height wherever you want it. It's really important to check the clearance between your ball joint collar and the wheel so they will fit after modifying. I use a piece of DOM roll cage tubing for the insert piece at the bottom, instead of re-using the cut out piece from the top. The result is better that way.

So Brad, if Ive got this straight on the SC/Carrera struts you just break the welds from the spindle casting to the strut housing and slide it up then re-weld?

Couldnt you the get a little more creative after cutting those welds and machine threads in the Strut housing and on the ID of the spindle casting use a couple of lock and jam nuts and have a Adj. assmbely?

Rich,

I could do that.. but its way cheaper to build a little ledge above the spindle and set a threaded aluminum collar down on it for a cheapy coil over conversion. The threaded collars and aluminum setup runs about 100$

Koni Converted:

B

Ok so this is getting a liittle OT, but please excuse the dumb Q?

What is the purpose of front coil-overs? if you have a gas preasureized strut insert * and torsion bar * and anti-sway bar that provide compression/rebound forces working in concert to keep the tires on the pavement, isnt the addition of a sprint overlapping one or many of those elements?
And adding weight?

I would think the torsion bars that would be removed would weigh pretty close to the weight of the additional springs.

Yes to everything... but.. The largest torsion bar I can possibly fit in a 914 or 911 control arm is 26mm. What if I need something bigger ?? I have to go to coil overs.

B

Oh.. Rich.

We remove the torsion bars.. NOBODY runs a torsion bar AND coil overs (at least not on purpose)

B

I believe the factory ran Torsion bars and coil springs together in the 911 RSR, early 70's.
It was a homologation stunt to circumvent having to keep the original spring medium as homologated, not sure of the specifics, but it has been done.

Raising the spindles also has a positive effect on restoring some height to the front roll center which is adversely effected by lowering the car, also exacerbated by larger Ø wheels & or tires, which fortunately allow additional space inside the rim to raise the spindle to recover....

Hayden PTBT

Ok makes sense. but what holds the A arms in place w/o the T-bars? never mind.... Im not likley to be running coilovers, my thought of threading the bodies was simply to address the lowering of the car w/o the cutting and rewelding of the strut tubes.
Seemed simpler to me.

The bushing/bearing assemblies hold the A-arms to the car.

Is lowering the front roll center undesireable because the rear roll center is going to be higher than the front no matter how low the car goes?

What does this all mean in terms of handling taking two different and extreme roll center scenarios and all other things being equal:
1. Front roll center is crazy-low from lowering the car and the rear is where ever it is from that lowering.
2. Front roll and rear roll centers are at factory (let's say european) spec height.

I've just started looking into this stuff (I've got Puhn's book) so any prospective, especially pratical prospective is appreciated.

Thanks,
Kevin

Kevin,

Without having the specific RC heights and geometry available, I will generalize, perhaps someone on the forum has plotted the 914 geomtery and has some definitive numbers?, with change due to ride height, roll etc. If so, they would be good to pad out this thread with data - assuming the data is correct.

The pivot axis of the front and rear suspension designs are perpendicular to each other, this has a significant effect on what happens to the RC height as the car is lowered or goes into bump travel.

The front suspension, with pivot axis parallel to the car centerline, will have a more radical vertical migration of the RC height as the suspension goes through bump and droop.
The migration of the RC height will be more than the ride height change - by some significant factor. This means that in bump (same as lowering) the distance between the height of the Center of Gravity (CofG) and the front RC will increase, making the kinetic roll stiffness softer.

The rear suspension pivot axis is roughly perpendiular to the car centerline, this means that in bump and droop, the vertical migration of the rear RC is pretty equal to the change in rear ride height. This means that the distance between the CofG and the rear RC is fairly constant and kinetic rear roll stiffness is relatively constant too.

If I had to speculate, based on the assumption that Porsche Engineers did a good job of delivering a balanced car in the stock 914 - regardless of skinny, hard tires - I would say that lowering a 914 all round, with no spring changes, would lead to a fundamentally oversteering (not necessarily evil) car. This ignores the lack of suspension travel issue and many other issues, but this explanation is centered on RC effects.

The oversteer would be a function of the front roll stiffness becoming progressively softer, therefore a split of roll stiffness more to the rear and a more oversteer prone basic package in a steady state condition.

Given that the kinetic roll stiffness acts in conjunction with the roll stiffness that comes from wheel rates and ARB rates, it's a complex closed loop, as I am sure any books you are reading will illustrate.

The raised spindles are really an effort to restore the FLWB (front lower wish bone) angle to replicate a higher ride height when the chassis is lower. It has multiple advantages, including restoring some camber and camber gain (actually reduces camber loss). The RC is raised too and this is one of those invisible factors that is difficult to visualize, whereas the camber gain etc, can be witnessed by simple measurements.

I think there is sufficient empirical evidence and experince available to discover how to set up a lowered 914. I can be pretty sure the lower the 914 the more front wheel rate is desirable, primarily for roll control. If you raise the front spindles, you probably find - at equal ride heights, the front ARB and springs do not need to be as stiff (to compensate for low front RC), overall grip should be higher.

Hope this helps in a practical sense?

Regards

Hayden PTBT

That answer is why this board is the best thing going...makes a lot of sense!

The front RC can be found by (this is a question): projecting a line from the inside edge of the front tire through the a-arm pivot axis? The intersection formed by lines projected in similar fashion from each front tire->a-arm defines the front RC?

The rear RC can be found by: ? The fact that the suspension pivots roughly perpendicular to the car CL makes rear roll center less intuitive to me. How does one define the rear RC?

With those two definitions I'll be happy to measure my car and put some data into the thread.

QUOTING from Hayden
"The migration of the RC height will be more than the ride height change - by some significant factor. This means that in bump (same as lowering) the distance between the height of the Center of Gravity (CofG) and the front RC will increase, making the kinetic roll stiffness softer."
That begins to explain shifts in a car's handling behavior; car understeers at low speeds then transitions to oversteer at higher speeds as the suspension gets compressed due to cornering/braking loads.

Good stuff.

Thanks,
Kevin

I dont believe thats all tru. I have tried that once. The struits were from 1988 Carrera. I think they were Boges. I am 99.9% sure about that and I have somewhere pics about them. The spindles and the struits were tapered. I was very disappointed when I found out that. I would have wanted to lower them...

Kevin,

Be careful not to make too large an assumption, the fact that all factors of vehicle dynamics are fully associated, makes it difficult to isolate particular issues.

Speed dependent US or OS can be as much to do with CofG - lengthwise, wheel rates, tires, tire pressures, etc, and so on.

Fortunately there has been some good empirical testing done in the past 50 years, it proves some isolated effects, but totally proves inter-dependance of all factors. The lowered 914's , will have some reduction in front roll stiffness from a lower front RC, but I would hesitate to say it explains a basic chassis trait.

It an extremely interesting topic to investigate and the more you understand, the more you realize there is to understand. The more you understand the more you understand the inter-dependance.

When I wrote of suspension geometry, I mean data recorded under pretty strict circumstances.
A car sized surface plate and decent measuring equipment being the very most basic neccessary equipment.
I would like to think that someone has gone to the trouble at some stage, but if they have, perhaps they are unwilling to share their hard earned suspension co-ordinate data.

Regards

Hayden PTBT

I have all this info "somewhere".. I havent had to reference it in quite some time.

Thanks Hayden for putting everything is "laymans" terms. Thes guy's will soak it up like a sponge.


B

Calculating roll centers - For the rear semi-trailing arms this is a little hard to put into words. The easiest way is to look at the drawings in the "How to make your car handle" book (http://www.amazon.com/exec/obidos/tg/detail/-/0912656468/102-0367153-1612966?vi=glance). It covers semi-trailing arms, MacPherson struts, Double A-arms, etc.

Jonathan

I found this good graphic illustration of how lowering ride height lowers the roll center, decreasing roll stiffness, per one of my previous posts.
Check out this and the info about semi trailing arms on the same page ( or nearby, you can find it!)
The suspension on the BMW's under discussion is pretty much teh same as the Porsche configuration.

http://e30m3performance.com/myths/Weight_T...t_transfer2.htm

The raising of the front spindles is an effort to get the lowered car, front lower control arm, adopt the angle of the un-lowered car and thereby restore some of the height of the front RC (reducing the distance between the vertical CofG and the RC.

Regards

Hayden PTBT