Setting up for autocross - suspension (extreme tripod action shots here!)

[daniel911T]

I did my first autocross a couple of weeks ago and my car was the slowest and most entertaining at the race I'm running a bone stock - comfort group - suspension with stock euro ride height and toe/camber/caster settings.

Here's what it looked like:











I have my hands on a full set of torsion bars from an 88 930 - 26mm rears and the 18.8 fronts. I also have the Koni front strut inserts from the same 930. I will be installing the rears, but I'm not sure about the fronts - is there a benefit to installing the same size bars that are 20 years newer?

Does anybody know if the valving is significantly different between the stock Koni shocks for an early 911 and the 930 shocks? Is there a benefit to using them?

The car does not have a rear sway bar installed, and the local PCA racers tell me that it isn't really needed on my car... comments? There is a front through body sway bar - it's got three adjustments and is presently on the middle setting. Would it help to make it stiffer or softer?

Finally, I'm planning on lowering the car - local recommendation was 30mm. Any other thoughts?

Thanks!
-Dan

[cgarr]

Really no rear sway?? That was one of the first things I put on my 69 right after the larger torsion bars. Yours looks like mine when stock. Tie those strut towers together too!

Before:


After:

[cgarr]

I have 28mm rear and 21mm fronts now mine is a 912 so it's lighter in the back, the 28's are perfect for my weight.

[daniel911T]

[QUOTE=cgarr;8002481]Really no rear sway?? That was one of the first things I put on my 69 right after the larger torsion bars. Yours looks like mine when stock. Tie those strut towers together too!

Before:


Weeee!

Your "after" shot is sorta what I'm looking for...

[cgarr]

Get some swayaway spring plates make adjusting at the track easy and your going to want to play with the height. I like spending other peoples money!

Swap out the track tires and your ready for the road again!!

[Trackrash]

It's down the slippery slope for you.

I have some suggestions before you start throwing random modifications at your car.

1. Take the performance driving school. Or what ever PCA zone 7 calls it. (autocross school?) PCASDR has an awesome school two times a year.

2. Then determine what level you want to compete at. Talk to the drivers of cars that are similar to yours in vintage and modifications. Ask what they have done as far as modifications. LOOK AT THEIR TIRES.

3. After a season of autocrossing decide what tires and wheels you want to use. This will determine what suspension mods (and how far to take them) you will need. Otherwise you could make the same mistakes I and others have made. I wouldn't have had to completely re-vamp my suspension three times if I had done that.

4. In the mean time, make sure your suspension's bushings, shocks, ball joints, tierods, and bearings are perfect. Then, set your ride height, corner ballance and alignment. You might also want to upgrade your swaybars.

Have fun like we did at Redwood this weekend. https://www.flickr.com/photos/mutantsurfing/sets/72157642767561444/

[mattipuh]

+1

[daniel911T]

The suspension has been thoroughly gone through, and the car has had a proper alignment and corner balance. I caught an amazing sale at Koni's official website - new shocks for my car were less than half the price our sponsor charges. They'll arrive somewhere around the end of the month.

The bushings have all been done, the wheel bearings have all been done, ball joints done, turbo tie rods installed: basically all maintenance done.

I have a vision - I want to make it be as good at autocross as possible while using Porsche parts, street tires, and staying on my 14" rims. The car is my daily driver, so I need to keep it tolerable.

[safe]

Originally Posted by daniel911T

I did my first autocross a couple of weeks ago and my car was the slowest and most entertaining at the race I'm running a bone stock - comfort group - suspension with stock euro ride height and toe/camber/caster settings.

Here's what it looked like:



-Dan

Wow! That looks scary, That is almost a "dual-pod"

A rear anti roll bar, 26mm rear t-bars and fresh shocks is a good start for an early car. After that the slope becomes steep...

[Trackrash]

14" wheels may be a challenge when buying tires. A second set of tires and wheels may be something to consider.

I would recommend adjustable sway bars, as long as you aren't worried about that bumping you in a higher class. Getting a good balance is important.

What Konis did you get, Reds (classic)?

When you had the car aligned, did you mention you were going to autocross?

[Driven97]

Holy cow.

[theclaw]

What he said, "Holy Cow!" Those are some wild shots.

[daniel911T]

Originally Posted by Trackrash

14" wheels may be a challenge when buying tires. A second set of tires and wheels may be something to consider.

I would recommend adjustable sway bars, as long as you aren't worried about that bumping you in a higher class. Getting a good balance is important.

What Konis did you get, Reds (classic)?

When you had the car aligned, did you mention you were going to autocross?

Yes - reds. They are single adjustable while of the car. The current fronts are of unknown age, the rears are also of unknown age, but they were high quality used when installed 3 years ago.

Strange thing - when I removed the old rear shocks, I wasn't sure they really needed to go because the car didn't bounce at all. When I took them out, the rods just fell all the way in without any resistance at all. They were completely dead. Again - the car did not bounce at all. I'm wondering if my fronts aren't in the same shape.

The alignment was done by a pretty amazing shop in Washington State, but I specifically requested a stock job. I had the car put right at the Euro factory settings in preparation for daily driving.

[daniel911T]

Specific question to the group:
I have a set of front torsion bars from an 88 930. They're the same size as the '69 stock.(although there is a lot of '68 stuff on my car - I should check for 18mm bars up front)

Is there a benefit to putting in a set of bars that are the same size, but 20 years newer?

[daniel911T]

Originally Posted by safe

Wow! That looks scary, That is almost a "dual-pod"

A rear anti roll bar, 26mm rear t-bars and fresh shocks is a good start for an early car. After that the slope becomes steep...

Believe it or not - that was not an out of control situation. I was hard on the throttle,which is why both back wheels are on the ground, and understeering while running for the finish line. They had the course set up so that there was a long fast right then a very quick left and straight on to the finish. That's why you see the "up" wheels switching.

It was fun, but pretty slow.

[Trackrash]

Originally Posted by daniel911T

Specific question to the group:
I have a set of front torsion bars from an 88 930. They're the same size as the '69 stock.(although there is a lot of '68 stuff on my car - I should check for 18mm bars up front)

Is there a benefit to putting in a set of bars that are the same size, but 20 years newer?

Not unless your current torsion bars are worn or rusted. When the front rubber bushings get old there is a tendency for the torsion bars to rub and cause wear.

[Driven97]

Took a few minutes to think about this, and I'm going to take a crack at what I think is going on.

DISCLAIMER: I'm early on my quest to understand suspension, so any percentage up to and including 100% of what is about to spew from my fingers may be incorrect. There are at least 3 people on this board who actually know this stuff, so hopefully they will chime in.

I think what we are looking at is a phenomenon called jacking. A suspension of a car has a roll center. It's like a pivot point that a call rolls around under lateral load. A car also has a CG, which is a way to simplify where the mass of the car acts. What you end up with is a lever with the mass trying to lean the car roll center. I believe this is called the roll couple.

Normally, suspensions are designed with a roll center around ground level or slightly above. I think I read this gives the driver good natural feedback as the car leans.

Problem is, while the CG stays the same, the roll center is dynamic - it changes with suspension deflection. Also the rear has it's own roll center, and a line between the f&r creates your roll axis. I don't know how the rear trailing arm roll center is calculated. But with the MacStrut front, the roll center lowers as the suspension compresses, and raises as the car raises.

Now you may be thinking, cool. If you raise the roll center to CG height the car will not roll at all, and that will be awesome. Problem is, when the roll center gets too close to the CG, the car exhibits jacking where it lifts the whole car. Old swing axle Triumphs were famous for this:


I think your front end is jacking. I think your aftermarket front swaybar is too stiff. I think it's not allowing your front end to compress, keeping your front roll center too high. I think the front of the car is just sort of tilting over, rather than rolling over and biting in.



I have the same suspension design and geometry as you, and bet I'm putting a fair amount more lateral load on the car. I have a lot of roll going on, but the car is hunkered down on those outside tires pretty good.

tl;dr if I'm right, there is more than one solution to try:

Easiest and cheapest is to soften that front swaybar. May seem counter intuitive when it seems like you have enough roll already, but as soon as that inside front is up it can't transfer any more load than it already is. I bet if you soften the front (move to the outer most holes) the front will compress and bite better.

Another option would be to lower the car a bit. I'm no expert, but it looks a little on the high side for performance purposes. If you have room on the front adjusters, you can give them a quick turn or two down the morning of an event. If you count your rotations, you can put it right back to where it was after the event and go back to your original alignment.

Next plan of attack would be to reduce the total roll. You'd have to go after the rear, as the front is apparently giving beyond all it can. That means more rear spring and/or adding a rear swaybar.

[stlrj]

Originally Posted by daniel911T

The car does not have a rear sway bar installed, and the local PCA racers tell me that it isn't really needed on my car... comments?

I would think that the addition of a rear sway bar would have been all that was needed to minimize the tripod action. That's what I would do first before trying anything else.

I really do not think that allowing the front to compress further would do anything to reduce the body roll, but a rear sway would do wonders. I am even considering a heavier rear sway for my 87 Carrera to reduce body roll to reduce the inside front lift as seen in the above photo. I wonder if they even make a heavier rear sway bar for an 87?


Cheers,

Joe

[Driven97]

Originally Posted by stlrj

I wonder if they even make a heavier rear sway bar for an 87?

According to our host the OE 21mm rear sway on your 87 is the largest factory bar. If you want to go bigger, you have to go aftermarket.

:Rant mode:

I think there is a big propensity in the enthusiast car world that the solution to every problem is to throw money at it. Buy buy buy. If you spend enough, then the problem will go away. Nobody takes the time to learn and understand what is really happening and why. These cars were blessed with a fair amount of adjustability straight from the factory. If you put in the time to learn, adjust, test, take notes, & repeat, you'd be surprised how capable you can make the car. But that's too much work, so fire up the Visa.

People buy adjustable shocks when you have no idea how to adjust them. Pick spring rates at random, choose your alignment specs from some random internet poster, never bother to see how something as simple as tire pressure changes affects the dynamics of the car. They listen to someone who says you need to buy this thousand dollar super adjustable widget because so & so has it on some race car.

I say, take advantage of all the options you have available to you for free first. Learn what everything you already have does, how it works, and why it was made adjustable in the first place. Yeah, it's a lot of effort. Hard work, even. But it's really fun work. When you exhaust all of your options, you'll have a deep understanding of what real problem you have. Then you'll know what part you actually do need to buy to progress instead of just throwing money and hoping it sticks.

:Rant off:

[javadog]

If you use the 930 rear torsion bars, use a larger than stock front bar. Add a rear swaybar. Consider using new Bilsteins instead of the Konis.

JR