Sway bars and rates, Some times I over think things a little Options

[Borderline]

914forme: the rear bar does have an 11" arm, however it acts directly (well almost directly) on the rear wheel. The front AR bar acts on the lower control arm, about 7" from the pivot point. My analysis shows the rear bar to have about 70% the stiffnes as the stock front bar. My analysis is based on how much force it takes to move the wheel 1". The stock 16mm front AR bar takes about 117# to move the front wheel 1" when the body rolls. The stock rear AR bar takes about 80#. this analysis treats the AR bar like a torsion bar half as long as the AR bar. If you assume that the AR bar link on the inside drops the same amount as the link on the outside rises, the centerline of the bar doesn't twist at all.

Sorry: didn't mean to hijack your thread. Always looking for other viewpoints on suspension stuff and trying to learn more!

Andrew: That "moment center" sounds a lot like the "roll center" That I've read a lot about over the years.

[Trekkor]

I've had good results with my Smart 31mm bar.


KT

[KenH]

Do not forget to take in to account the the angle of the drop-link as it is moved along the attachment arm.

Ken

[Downunderman]

1.25" bar adjusted 4.00' out = 4,216 lbs per inch. I suggest you make up some custom hardwood springs for the rear. That probably exceeds the torsional strength of the chassis. Maybe you need a welded in cage.

I'm with JP on softish spring/stiffish AR bar. But I don't do autocross and it looks like a very different discipline to most other forms of motorsport when it comes to setup. I have found F 19mm TB and 20mm AR bar and R 180 and 19mm AR bar to be a fairly good compromise for street/track/rally. Just screw the bars up when you want to go fast.

[914forme]

Howard the number you quote was in inch pounds, not foot puounds! I might need a cage, I don't want to take the hit on weight. But then again, I could loose else where playing with the rules a little. Since I can go 100 pounds less than the Factory specified weight for my chassis, and take 0 points.

A Engmann Log kit will be mine soon also, install this winter, can only help. And I have a few other tricks up my sleeve also.

Do you run slicks or are you just an oversteer maniac? That rear bar is huge compariad to mine, and the front is less than my current setup? Flares and big slicks what gives?????

[J P Stein]

Do you run slicks or are you just an oversteer maniac? That rear bar is huge compariad to mine, and the front is less than my current setup? Flares and big slicks what gives?????

Howard runs road rallies in ....the far SW....way far.
These are rally (really) road races like World Rally.....the guy with the fast time wins.
Near as I can figure, Howard does what he needs to do to his suspenders so's
he go faster than the other guy over the open road.....no small feat considering the trees & other shittage lining these roads. Some of his alignment specs are much wierder than anything that comes from AX.

He wrote once that he runs 3 deg caster.
One assumes that is to negate some of the self centering features of the 6 deg that AXers run. You really don't wanna hear how the self centering of the front suspension can be used to an advantage in dire AX conditions (IMG:style_emoticons/default/biggrin.gif)

Yes, these threads tend to wander thru the subject matter when suspension work comes up. Those of us that pay attention to this stuff can learn all kinds of interesting crap....useful or not. (IMG:style_emoticons/default/laugh.gif)

[Brad Roberts]

Easily one of the best threads I have ever seen posted on this site (IMG:style_emoticons/default/clap56.gif)

If you think Brad is the greatest AXer to come down the pike, go with his thinking.

I'm the first to admit that I suck at AutoX'ing. I can get a car around the track, but I feel the two damn near share nothing in common when it comes to setup (for serious AutoX cars)

One of the main reasons I subscribe to the soft spring theory: I can only get 26mm Tbars into a 914 control arm. Not everyone is running coil overs. Also: I cannot buy springs in 5 or 10lb increments. It requires me to run tender springs and most PCA/POC classes for 914's dont allow tenders.

Ask me about the setup on a Boxster or GT3 and it changes to higher spring rates and smaller bars.

Damn. This is a REALLY good thread.


B

[DNHunt]

I really wish I hadn't read this. After 3 years of reading posts and learning I've gotten to the point i can take care of most of the day to day things and repair stuff I bust. Now I realize there isa whole world of mystery I need to look into. Damn you guys!

Dave

[Brad Roberts]

Dave,

dont take this stuff too seriously. It is not like we are dealing with a new car that has NO devlopment. I promise I can give you a setup that your can drive.

I have found this with pro's: they can drive the wheels off of anything you put them in as long as the setup is SAFE. You can throw all the engineering at it you want.. it still comes down to what the driver is most comfortable with. I know where this starting point is for most narrow body 914's on 205 sticky tires.

Sometimes people spend too much time worrying about the setup when they should be getting seat time on a "marginal" setup.

Trying to teach someone to communicate what the car is doing, I find, is more difficult than the actual setup changes needed to correct something. Is it oversteering or understeering at corner entry? Is the car neutral at the apex? Is it oversteering or understeering at corner exit? Is it power on understeering or oversteering in XX corner? Once you understand the questions.. making the changes becomes easy.


B

[TravisNeff]

You could do the figuring the easy way - check the Smart Racing catalog, they have spring rate ranges (for adjustable bars) for their big anti-sway bars.

[J P Stein]

What Brad says is true. There are times when stuff happens ....the tires go off, the course doesn't suit your car, the moon is full...yada. These are the times when you need to do the best driving you can to over come your real or percieved problems.
It's the time to practice making the car rotate when it doesn't want to. Braking way late into a Chicago box and still making it thru and other such stuff. If you loose it, you've learned something, eh?

Tho I have never driven Dave's car, I have ridden along with his son at the wheel.
Decent handling & power....enuff poop to kick the back end out as required....a good street/AX combo. No glaring faults at the speeds he was going.

The boy hadn't (at the time) gotten to the full time controlled ragged edge needed to take a step up to the fastest of the 205 bunch. That's where the faults are found....both in the car and in ones driving.....trust me on this....Mr Kotzian again demonstrated the difference between the ragged edge as I do it and a controlled ragged edge as he does it....it's about a second & a half (IMG:style_emoticons/default/biggrin.gif)

[Borderline]

Good to have the non-club back up and running! I did the AX at Marina last Sat. I'm still very slow but had a great time. Adding the rear sway bar and going a little stiffer on the rear springs made all the difference in handling. I'm still trying to figure out what it was doing!!! It seemed to turn in pretty well at corner entry and a little oversteer at corner exit. It would call it power oversteer, but I don't have any power to induce it. It really didn't like throttle off in the middle of a corner. I've really got to learn to keep my foot in it and not back off when things get a little lose. It was a little tail happy in the chicane so I stiffened the front shocks some. It was pretty well behaved after that. I think I'm going to leave it alone for the next couple events and see if I can improve my driving. I love to tinker with settings and its going to be hard just to leave it alone.

This is a great thread. I always thought that changing the sway bar diameter was a very large change in stiffness and that adjusting the arm radius was minor tuning. But, by adjusting my 19mm bar in about 1.5", it can be the equivalent of a 22mm bar! I love this stuff! (IMG:style_emoticons/default/boldblue.gif)

[914forme]

This is a great thread. I always thought that changing the sway bar diameter was a very large change in stiffness and that adjusting the arm radius was minor tuning. But, by adjusting my 19mm bar in about 1.5", it can be the equivalent of a 22mm bar! I love this stuff!

Glad to hear you got it balanced or at least closer to balance for your setup/driver. In reality, I can make my new 31mm bar as soft as a stock 15mm, or as hard as I can possibly imagine. I have a felling once I get the front bar setup, I might be looking to do the same with the rear bar. Adjustable rears would make it oh so much easier for me to screw up my cars handling even more. (IMG:style_emoticons/default/biggrin.gif)

Take care, Stephen

[John]

I like this thread. It's the same thing I went through 15-16 years ago when trying to set up the track car. While reading what the car was doing, we felt the need to get heavier springs and sway bars.

I did the same (or at least very similar) sway bar spring rate calculations, as well as the torsion bar spring rates and came up with a setup that was well balanced and took a minimum of tweaking the front sway bar to make for a very neutral handling car that we still push very hard on the track today.

The comments made about seat time and getting to know what the car is telling you is one of the most important steps in "dialing in" the suspension. Without that feedback, you can throw a ton of money into swapping out parts for little or no benefit.

One thing to really keep in mind when going to these MEGA front swaybars is that the swaybar is still transmitting it's force to the body through some relatively thin sheet metal. The inner wheel well can bend and begin to tear with even a small bar if the arms are made short enough. The metal in those areas should be well reinforced (and not just with the backing plate). I have seen the mounts tear out the same size as the backing plate.

just some food for thought.

[914forme]

John, all that is good info I have taken the swaybar backing into consideration from day one with this chassis. but I was using a much smaller bar. So for the new king of sway bars I am taking notes from Nascar boys and building a new setup, different from most if not all 914s out there.

One realization I am making is as I get closer to the ragged edge of auto-x, my car is becoming much less of a street car. I am considering taking it off the street, and towing it to events now. If I do that spring rates can go way up. I do so enjoy driving the car though it is usually only to and from events.

So here are the details of the new mounts, and systems. I am basing my design off the fact I will be using 1.25" end sway bar. I am installing a central tub, into the car, 1.75" ID tub, from side to side, approx. 34.5" long. The sway bars are 37.5" long, the arms are about 1" thick. So that gets me down to 1" of play for bushing collar, and swaybar collar. These will be bolted together at first to finish mock up. Then it will all be welded.

Outside I will add a 16 gauge plate from dimple down spreading out as I go down to rack area. Inside I will be adding a larger plate that goes front to rear, and bends to tie into the front trunk wall. I will also add a box section to tie the support tube and the lowest corner diagonally. It adds a third dimension to the shear points and strength the entire assembly. This assembly should not see any side loading except from the resistance of the bar trying to play in the bushings. This will be taken up by the collars on each end.

Added some simple sketches of the design. Advantages , I can now swap bars all day long. Since the bushings are the same, if I have too much front bar, I can go down a size, or go up. Until I hit the inner tube wall, with clearance.

Again just goes to show, I over think this stuff. (IMG:style_emoticons/default/biggrin.gif)

[groot]

Hmmmm.... kind of like this?

I don't think your support tube is required..... If you use rod ends on your end links you shouldn't have side loads on your bar....so all of the load into the stabilizer bar should be shear to the mounting plane.....

[914forme]

See I over think things.

Kevin,

Where did you get that bearing? And then see I am never a pioneer, that is what is so wonderful about this non-club. Somebody has already invented the wheel 3x over.

Take care, Stephen

[914forme]

Okay on a side note JP was asking if I knew corner weights etc...

The answer is yes, I do know my corner weights. But What I was trying yesterday was to figure out true spring rates as they applied to the tire contact patch.

So out came the jack, a scale, a set of chains, and the dreaded jack stands. I needed to fix an oil cooler leak anyway.

So I put it up on jacks, chained the chassis down to the floor. Placed the scale onto of my jack, with a backer plate. Jacked up just under the tire. My scale only goes to 300 pounds, it is a shippers Digital scale. So I would jack it up, get contact on the tire, I got my tape out and measured a location on the wheel as reference. Zero out the scale, and jack up 1 inch. Took note of the readings, and repeated this 5 times. Added the numbers together and averaged them out.

Now this was with out sway bars added I disconnected each one of them.
Front side I had 196.5 lbs and 193.3 lbs. Rears I had 215.1 lbs, and 217.3 lbs. I am confused by the numbers. Is this the true number via spring rate or does this also include unsprung weight. I was expecting the rates to be less than the calculated rate of the springs. Due to real world variations, I was not expecting it to be more.

So possibilities I see right off the bat with this method.
1. it also took into account my wheel and tire weight plus part of my suspension arms and shocks.

2. the Gas Bilstiens add to the rate.

[Borderline]

Kevin: What am I seeing in that photo? You've obviously got coil-overs and have replaced the lower arm with rods. Is the lower end of the AR bar link attached to one of the rods? You must have used Andy's camera (IMG:style_emoticons/default/poke.gif) You've got a very wide range of adjustment. How many of those holes in the arm have you used?

[groot]

Sorry, I don't remember where I got that bearing.... it was 2 years ago and I ordered it from some industrial bearing supplier off of the web.... It's a pretty cool piece, it has two stamped pieces that allow the bearing to pivot and the bearing is a ball bearing unit that fits around the 1" stablizer bar end and uses set screws to hold it. I'm a big fan of using ball bearings on a stabizer bar, one more way to reduce stiction. McMaster Carr has stuff similar, but not exactly what I wanted. Bar and arms are from Speedway Engineering.

I had the bar set where you see it, but with the new front end I've stiffened the bar 2 more holes this weekend. Still oversteers after about 6 laps. Still working on that problem.

The rods are there because I moved my inner pivot points for better geometry and incorporated a double adjustable strut insert. There are details in my blog and in older threads on the subject.