Handling issues - need adjustment advice Options

[Brian Fuerbach]

I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.

Thanks for the offer. will pm you after an alignment.

[Brian Fuerbach]

Soften the end that's not working. FARB is probably too stiff. Probably too much front toe-in too.

(IMG:style_emoticons/default/agree.gif)

I think you've got to much stiffness on the front between the dampers and the Anti-roll Bar (ARB).

As Brant suggested. Move the ARB links toward the absolute end of the adjustable bar. I.e. increase the length of the arm - decreasing stiffness of the front ARB.

As Roblav1 suggested. Dial out dampers (softer). Adjustable dampers are only adjusting rebound damping. Lots of front rebound damping ends up fighting the ARB on the inside wheel. In additon, the net effect of too much front damping only further stiffens the front end in addition to the what the ARB has already added.

What we're working on here is to soften the front end relative to the rear.

My impression is that you like the extra body roll control that the front ARB added but that it's been over done with the 19mm front bar. I don't think you have mentioned yet if there is a rear bar. The OEM set up added a bar on both front (15mm) and rear (16mm). The dual bars provides a more balanced split of body roll control. If you don't have a rear bar, you're trying to do all roll control off the front end which stiffens the front end, inducing steady state understeer.

When you added some damping to the rear, you stiffened it - which has the same net effect as softening the front end relative to the rear. Hope this makes sense the way I've written it.

All tuning is done on a relative basis. You can soften the front or stiffen the rear for the same net effect. Sometimes you will have to do both to achive a desired result. But for right now, no need to get into additional rear spring or damper changes. Just work on one end of the car at a time with the overall direction of softening the front relative to the rear. Ideally, you work on the end you want to affect. I.e. if you want to soften the front; do the work in the front. When you run out of front "knobs" to turn then you can start stiffening the rear further.

I'm in Pasadena and do some suspension tuning on the side if you want to drop by and show me what it's doing.

Take Yeahmag up on this. It is always way easier to tune when you can see and feel what is happening vs. trying to do it by words on a forum like this.

Your explanations are very understandable and appreciated. I do not have a rear bar but will soften the front damping and arb to full soft and see how it goes.

I plan on getting a real alignment and make the suggested changes before visiting Yeahmag.

I have often read here on the forum that a rear bar is not desired by most. What is you opinion?

[gereed75]

Softening the front roll bar won't hurt but a 19mm is not in itself out of line assuming rear springs are reasonably stiff (110 -140)

There has been no mention here that I saw about front tire pressures or did I miss it? High tire pressures could certainly cause the symptoms you describe

[rhodyguy]

IIRC the Koni instructions stated neither full soft or full hard on the settings.

[Superhawk996]

I have often read here on the forum that a rear bar is not desired by most. What is you opinion?

My opinion is that I want a front AND a rear bar. I want to be able to manage roll couple distribution between front and rear as independently as possible.

Roll couple distribution is affected primarily by spring rates and ARB rates. If I don't have a rear ARB, then the only other knob I can change is rear spring rate.

The problem with changing spring rate is that cascades to other things like ride quality degrading as the spring rate goes up. Likewise as spring rate goes up, a fixed rate damper tends to become underdamped or needs to be retuned for the new spring. Aftermarket springs also have a terrible tendency to affect ride height as spring rates go up.

The whole idea of ARB's when they were "invented" was an effort to decouple roll rate from spring rate to get better roll control without the ride degradation.

If you look under most cars, you'll find both a front and a rear - they are typically standard equipment for safety/handing reasons. Contrast that to the 70's when roll bars were often optional equipment.

[Brian Fuerbach]

Softening the front roll bar won't hurt but a 19mm is not in itself out of line assuming rear springs are reasonably stiff (110 -140)



There has been no mention here that I saw about front tire pressures or did I miss it? High tire pressures could certainly cause the symptoms you describe

The bar is a hollow 19mm if that makes a difference. The rear springs are an unknown. Can the diameter give an indication? What is the diameter of a stock coil?

Tire pressure 26 front 29 rear on Pirelli P6000 195/65R15

[dr914@autoatlanta.com]

you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking. Things get better with a full tank of fuel. Is that just the nature of the 914, full tank factored into weight bias, or can the suspension be tuned to emulate the weight.

Here is what Im working with;
-19mm adjustable sway-bar set about 1” back from full soft.
-Koni yellow adjustable shocks
-Stock front torsions
-Rear springs are aftermarket (reddish orange color) but I do not know the poundage.

Any input would be appreciated.

[Brian Fuerbach]

you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference

When driving large sweepers like freeway on ramps at high speed I experience what I can only describe as front end scrubbing. Not understeer, more like the front is just not planted and tracking. Things get better with a full tank of fuel. Is that just the nature of the 914, full tank factored into weight bias, or can the suspension be tuned to emulate the weight.

Here is what Im working with;
-19mm adjustable sway-bar set about 1” back from full soft.
-Koni yellow adjustable shocks
-Stock front torsions
-Rear springs are aftermarket (reddish orange color) but I do not know the poundage.

Any input would be appreciated.

I would have to disagree. The addition of the front bar transformed my cars handling for the better. But with that said, maybe a rear bar would be twice as good.

[JamesM]

you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference

Sure you can, just beef up the rear springs and get the weight distribution/ride height setup properly.

I run a 21mm front bar with no rear bar and 180lb springs on my autocross car. Absolutely love how it handles. Its setup to where I can adjust my angle mid corner with the throttle.

The one 914 i have setup with stock front and rear bars gets far to lively in the rear end for my liking.

[Brian Fuerbach]

you cannot put a front sway bar on a 914 without a rear one, or the car will plow even more than in stock dress (under steer). best to install 15 front and 16 rear to get excellent spot on handling and steering response disconnect the sway bar and drive again and see the difference

Sure you can, just beef up the rear springs and get the weight distribution/ride height setup properly.

I run a 21mm front bar with no rear bar and 180lb springs on my autocross car. Absolutely love how it handles. Its setup to where I can adjust my angle mid corner with the throttle.

The one 914 i have setup with stock front and rear bars gets far to lively in the rear end for my liking.

I like the way the rear feels just the way it is, but unless I have a full bag of gas the front does not inspire confidence.

[Brian Fuerbach]

So I talked with the PO today and he thinks that the rear springs are in the 70 to 80#range. Not sure of the brand though. Would a higher pound spring be added to help balance the the 19mm swaybar? Thinking 100# as long as the ride does not suffer too much.

[Shivers]

Well, looks like it is still a hot topic. Years ago all that Weltsmiester stuff came through here, got mine from George. To get a rear bar or not to, 19mm is too big for the front ...I got the front and rear, 19mm for the front, 140 lb springs for the rear and I think the front TB's were 21mm. Now I was no expert suspension doctor so I had it set up by Steve Floyd at european auto, he was. He says to me "Now all you have to do is drive" and he was right. At this time I'm adding Bilsteins front and rear and better brakes. I had KYB's and I'm really looking forward to the Bil's

[Superhawk996]

So I talked with the PO today and he thinks that the rear springs are in the 70 to 80#range.

Not likely. 70 or 80lb/in would be very light springs.

OEM springs are claimed to be around 100 lb/in. Without going into a spring dissertation, there is way more to a spring than simple rate but (IMG:style_emoticons/default/confused24.gif) that is the way the aftermarket handles spring marketing.


Here are the OEM spring parameters:

Wire diameter 9.6mm
Number of coils 11.5
Effective coils 10.

Visually those springs on your car look like they have thicker wire diameter than stock springs. Really the only way to know would be to put them in a spring tester that that compresses a given distance them while simultaneously measuring the load force changed.

I just purchased a set of 100 lb/in springs from 914Rubber. I'll post a photo later today for visual comparison

[slivel]

Suspension dynamics were interesting to me as a club racer who spent lots of time and money developing my car over 23 years. When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes. This includes things like springs, shocks, sway bars, corner weight, unsprung weight, wheels tires, alignment settings and probably a few more. I recommend a web search using the search term "suspension frequency". Things like wheel rate and motion ratio and the natural frequency of the suspension will be presented.

This is a cut and paste form a quick search:

Common suspension frequencies:

1.0 Hz - passenger cars
1.25 to 1.75 Hz - sports cars
2.0 to 2.5 Hz - autocross and racecars with low downforce
2.5+ Hz - high downforce racecars
1.45 Hz - Subaru BRZ (front and rear)

Higher frequency suspensions get jiggly and are obnoxious and street cars and they tend to bounce over rough surfaces. Race tracks that are rough require suspension tuning (lower frequency) to get max performance vice smooth tracks.
Auto manufacturers have compromise settings that you can move away from in either direction depending on the result you are seeking - Cadillac ride or McLaren ride.
The wisdom and experiences here on this forum can help get you where you want to be, but some research will also help a lot. It's a process. On my car with no wing and little downforce and racing on a wide variety of tracks/surfaces I used less than 2.0 Hz.

[Superhawk996]

When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes.

(IMG:style_emoticons/default/agree.gif) Truth!

[Shivers]

Suspension dynamics were interesting to me as a club racer who spent lots of time and money developing my car over 23 years. When you move away from the factory equipment, you must consider the entire system to achieve a correct and maximum performing result for your purposes. This includes things like springs, shocks, sway bars, corner weight, unsprung weight, wheels tires, alignment settings and probably a few more. I recommend a web search using the search term "suspension frequency". Things like wheel rate and motion ratio and the natural frequency of the suspension will be presented.

Oh Holy Physics Batman! (IMG:style_emoticons/default/sad.gif)

[Superhawk996]

Here's the photo of 914Rubber 100 lb/in springs and measurement.



A bit thicker than 9.6mm but close accounting for coating thicknes.

[Brian Fuerbach]

Here's the photo of 914Rubber 100 lb/in springs and measurement.



A bit thicker than 9.6mm but close accounting for coating thicknes.

My springs measure at 10.4mm in diameter so i am guessing 100lb? I found the attached chart that shows the stock spring specs.

This weekend I loosened up the front swaybar all the way and took a drive through Santiago and Trabuco canyons. The bar is a GPR 19mm and at full soft is supposed to be close to the stock rate. This really loosened up the front end in general. Steering feels lighter and less controlled, but smoother for sure. Gonna hit the sweepers this afternoon on my way home and see what is does.

How low does the car have to be to experience bump steer?

[Superhawk996]

I found the attached chart that shows the stock spring specs.

Can you post http link to that chart? It is interesting and I don't think I've ever seen that.

I'm not fully sure I believe those rates. At 50 lb/in it would take 10 inches of spring pre-load to support the approximately 500lbs of corner weight that a 914 will have. Seems to me they would have to be very long springs to get the pre-load needed to support the vehicle.

I was going to assemble my springs tonight but I'm thinking maybe I need to do a rate measurement just as a rationality check to this chart.

[Brian Fuerbach]

I found the attached chart that shows the stock spring specs.

Can you post http link to that chart? It is interesting and I don't think I've ever seen that.

I'm not fully sure I believe those rates. At 50 lb/in it would take 10 inches of spring pre-load to support the approximately 500lbs of corner weight that a 914 will have. Seems to me they would have to be very long springs to get the pre-load neeed.

I was going to assemble my springs tonight but I'm thinking maybe I need to do a rate measurement just as a rationality check to this chart.

I did a google image search and the chart came up which led me back to 914world. I took a pic with my phone so I dont have the link. PM me your number and I will text the image to you.

Please share your finding on the 914rubber springs. I was thinking of ordering a set.