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Suspension Set-up

Hi All- I'm experiencing a handling problem that is best described as dartyness. The car will literally become difficult (two hands on the wheel) to keep in straight line when a road is crowned or has any imperfections. I don't think it is a mechanical issue, maybe more of a set-up thing. The car just seems unstable. I'm most concerned about the straight line stability, the faster you go the more effort it takes to keep it pointed where you want it to go.
Car: 76 Turbo DE car, 2250 lbs.
Torsion Bars 23 front, 30 rear
Bilstein sports all corners
Turbo tie rods with SRP bump steer, shock tower support bar
SRP rear mono-balls on trailing arms
Weltmeister sways 22mm front & rear
Fikse 9 front, 11 rear, Hoosiers
Last alignment: lf -1.1 camber, 5.0 caster, .15 toe
rf -1.2 5.1 .14
lr -1.6 .12
rr -1.5 .12

Why does this car handle so poorly?
I also own an 86 with a few bolt ons that is far more predictable. Any DE or race guys have any ideas? Thanks-Jeff
Old 01-03-2009, 01:50 PM
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The car is to light for that set up, 2250 lbs and set up as if were 2800 lbs, will act like a stone skipping across water. WE set mine up with a 934 coil over package,19 mm front 22 mm rear,she behaves awsome.
Old 01-03-2009, 03:38 PM
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Have you swapped wheels and tires to see what that does? Poor tires can make it handle like a dog.

What position do you have the sway bars adjusted to? I have mine full stiff up front and full loose in rear, but my car weighs 2950 lbs.

Are those solid or hollow torsion bars? You may need to go to a litlle smaller bar in front.

Last edited by A930Rocket; 01-03-2009 at 06:09 PM..
Old 01-03-2009, 06:07 PM
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Your camber settings are not that extreme, but they will add to the dartiness in light of the stiffness of all the other changes you have made to the suspension.
However, I think the main contributor to dartiness is toe settings.
Now if you have positive toe on the front wheels that will definitely make it handle like you describe. You do not say whether it is a positive toe you mentioned or negative. Likely if it were set up for track duty someone gave you positive toe out.....for better turn in response.
The rear is even more sensitive to toe settings and from what I understand you should never have positive toe on the rear wheels in a 911 especially. This will add to severe oversteering tendencies and instability.
Find out what your toe settings are and you will want to run slightly negative on the front and definitely negative on the rear. You will loose turn in at the track but will make for high speed stability in a straight line.

Fred
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"

Last edited by fredmeister; 01-03-2009 at 06:18 PM..
Old 01-03-2009, 06:16 PM
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Hi Guys- Thanks for the input. To answer a few of the questions asked, I will clarify the info.
Turbo934- The car maybe to stiff. Maybe I should have custom valved the shocks also? It's been an evolution, until this year the car weighed 2550 but still showed similar handling tendencies. I'd love to go coilovers but budget won't allow this winter. Did the rsr coilover setup use both torsion and coilovers?

A930ROCKET- I did try my other set of rims with different tires. Same results. The torsion bars are 23frt and 30 rear solid and my sways are set a bit tighter in front than in the rear.

FREDMEISTER- Those numbers are positive toe settings. Maybe this is part of the problem? I will take the car and get it re-aligned and balanced, just need some settings that are proven. Also if anything part wise needs to be changed better to do this before the alignment as well.

Thanks to all and keep them coming- Jeff
Old 01-03-2009, 08:23 PM
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Hoosiers?

Been down this road, lots of crown on the roads here too. The only thing which worked for me is non 'R' tires which still have tread. It sucks but the car drives normal. Getting the car to and from the track on race compound slicks is a white-knuckled-panic to say the least.
Old 01-03-2009, 08:42 PM
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I am with Fred - if it is toe out, your car will be very darty. And, hoosiers (or R-compound) doesn't help as they tend to make steering more responsive; i.e. will jump / turn quicker.

BTW - also remember that Hoosiers don't have steel belts meaning any small sharp object on the road may easily pinch it...
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Old 01-04-2009, 06:45 AM
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What size tires are you running? Fat front tires will make the car follow the unevenness of the road.

If your running Hoosiers they typically need a lot of neg. camber. I run -1.8 fronts and -2.8 rears using 245's front & either 295 or 315 rears.

A Rocket: if your sway bars are maxed out then your torsion bar or spring rates need to be re-evaluated. The sway bars should be pretty close to the middle, and are used to fine tune the suspension for different tracks and tire wear. They also don't perform well when they are maxed out to the tightest setting.

The torsion bars size seems o.k. There are a couple of different schools of thought on size. Some guys like a very stiff suspension and soft like a softer suspension. Depends on who sets the car up.

Revalved shocks will make a significant improvement in handling over the stock shocks. I swapped out my re-valved rear shocks for adjustable Wevo/Ohlins shocks which improved the handling even more.

Coilovers are a nice up grade but not a necessary unless you can't get the car stiff enough using torsion bars. They make it easier and less expensive for car set up. And easier and less expensive to change the spring rates.

I've seen RSR's set up with torsion bars and coil over helper springs.

I would look for a good race shop in your area and have them look at your entire suspension set up.

I have a used set of rear rsr shocks revalved to SmartRacing F40 if anyone is interested. They can be used with torsion bars or springs.

My n.a. race car weighs 2350 lb. w/o driver. Current set up is coil overs w/400 lb fronts, 500 lb. rears, S/R re-valved f40 front shocks, Wevo/Ohlins rears, S/R 31mm front sway bar, 27mm rear sway bar. 245's front and either 295 or 315 rears.
Old 01-04-2009, 06:49 AM
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Hey Guys- I'm certain it's not a tire/rim issue. I use the Hoosiers on track and have another set of Yokos for anything else. The rim sizes are 9" up front with 245's and 11" rear with 315's. The car will be a dedicated track car once I get this issue sorted. Wondering if I should just bring in the toe and increase neg. camber all the way around? What about the caster? Crazy thing is this alignment was done at a pretty good race shop. I'm wondering if they rushed on it or this is the set-up they feel works for this car. After taking it to Road America I know this set-up is off. But what specifically, I don't know. Thanks-Jeff
Old 01-04-2009, 03:07 PM
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Hey there,
I've got 23/31 t/bars, 22mm frt & rear sways, Bilstein h/d sports all 4 corners, Fikse 8.5 x 17 fronts & 11 x 18 rears, running B.F.G. KDW's, RSR bump steer kit, front tower brace.
The car is slammed 2-3/4" below Euro spec.'s
I have the rear sway at 3/4 stiff & the front sway at 1/4 stiff.

1st. set-up, 1/8" positive toe out....whooa..can you say darty! Hell I thought I was in Irish bar on St. Patrick's day at 2am!!
Drove seven miles that way, then turned around and went right back to the alignment shop. Changed to 1/8" negative toe in. Much better!!

Mark
Old 01-04-2009, 06:39 PM
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Mark, thanks for the info. I think I've been to that Irish bar! It must be the toe thats killing my handling. How much negative camber are you running? Caster? Thanks Again- Jeff
Old 01-04-2009, 07:43 PM
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Hey there Jeff,
I wish I had written down all the spec.'s, but I didn't. It all started with me lowering the car and putting WAY TOO many new parts on ALL at the same time. Before we got to the point of a road test. We had already done several trial & error set-ups. My main problem was getting as much rear camber out of the set-up. With how low I went with the car I was at approx. 2.5 degrees of rear camber. That was way too much for a street car, I would have gotten zero tread life.
So anyway, to make a long story longer, the front spec.'s were the least of my concerns. Sorry for letting you down with the #'s.
Mark
Old 01-05-2009, 11:03 AM
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Hey man, in line with what everyone says, I think it's the toe. If you are going to use the car on the track primarily, try toe out in the front (1/8" to 1/16" inch total), and make sure the rear has toe in. My setup is similar to your's, but with more weight. I run 17x9x11's, on R comps, the car weighs 2800lbs, with 22/30 torsions, Smart Racing antiroll bars (#31F-full soft, #23R adjusted a bit stiffer than midway), Elephant Poli-Bronze/monoball all around, and Elephant ASP/Quick Change in place of the spring plates, and my suspension setup is:

F camber -2.89 (too much based on temps), 1/8" toe out total, and max caster (shock top hats pulled back as far as possible)

R camber -2.25 (less than front 'cause I'm running the Elephant Racing ASP), and 1/16" toe in total.

Handling is very neutral, and there is just a little bit of dartiness in straight line, due to the front toe. This is expected, and not a real issue on my car. I would suggest adjusting your toe settings and see the difference. For custom shock valving, you can't go wrong with Rich at Smart Racing or Chuck at Elephant racing. I have done business with both, and highly recommend.

Good luck,
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Last edited by Garen; 01-06-2009 at 04:27 AM.. Reason: wrong camber info - now fixed
Old 01-05-2009, 11:30 AM
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Originally Posted by kupcar View Post
Hi Guys- Thanks for the input. To answer a few of the questions asked, I will clarify the info.
Turbo934- The car maybe to stiff. Maybe I should have custom valved the shocks also? It's been an evolution, until this year the car weighed 2550 but still showed similar handling tendencies. I'd love to go coilovers but budget won't allow this winter. Did the rsr coilover setup use both torsion and coilovers?

A930ROCKET- I did try my other set of rims with different tires. Same results. The torsion bars are 23frt and 30 rear solid and my sways are set a bit tighter in front than in the rear.

FREDMEISTER- Those numbers are positive toe settings. Maybe this is part of the problem? I will take the car and get it re-aligned and balanced, just need some settings that are proven. Also if anything part wise needs to be changed better to do this before the alignment as well.

Thanks to all and keep them coming- Jeff
My 1976 930 weighs 2450 with the gas topped off, how much gas did you have when you got the 2250 reading?

I do not think weight has anything at all to do with the issue because you had the problem before and after.

My car handles ultra stable in a straight line and I was tearing it up over some bad country roads the other day.

The way I had my alignment and camber and toe-in set up was EXACTLY according to stock Porsche factory specs for the 930.

Trust me, Porsche road settings work well in the real world.

I would set everything back to dead stock and then tweak it from there if you aren't happy.

Bisteins are not going to make your car's front end hunt, they just make the ride harsh over potholes generally, and they might not rebound quick enough for a lightweight car which would also not cause the car to hunt directly. Smart Racing Products is having a sale on their unbelievable Fox Shocks right now. Those shocks blow away re-vavled Bilsteins. But not the problem, IMO.

One thing to realize is that the car just plain might be too stiff with 22mm sways and big tires and the track settings for bad roads. But you won't know that until you sort out the dartiness...
Old 01-05-2009, 02:34 PM
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Going back to your original question:
I would try 1/16 inch toe in per wheel at first and maximum caster.
The camber should be as much as possible too and will probably land about neg 1.5-2 degrees on the front. This is aggressive for street but is needed for track day work.
Try to set the rear neg 0,5 degree more than the fronts....but get what you can out of it.
The rear should have 1/16 inch toe in regardless....never toe out.
This should get you in the ballpark and then tune in handling with the sway bars and tire pyrometer.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
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Old 01-05-2009, 02:58 PM
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Temporarily went from 275 to 255 up front - went from semi-darty to extremely slow turn in....
Little things make a BIG difference.

99% track car here -
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Old 01-05-2009, 03:25 PM
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Temporarily went from 275 to 255 up front - went from semi-darty to extremely slow turn in....
Little things make a BIG difference.
What width of wheels are you using? Did you go from 275/40/17 to 255/40/17? Both the same make and model of tire? The narrower tire shouldn't hurt turn in but perhaps overall grip
Old 01-05-2009, 06:05 PM
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Makes sense - with beaucoup negative camber, the overall contact area + the offset contact area relative to hub centerline has changed - and thus the way it behaves upon turn in.
~~~~~~~~
Kupcar, I'd almost say your experience is normal. Yes, normal.
My car is pretty stable ~~on the race track~~ in a straight line - with nice turn-in.

I'd also say it behaves pretty much the exact same way yours does - it is a HANDFUL on city streets:
Heavy, heavy steering.
Wicked rip--it-outta-your-hands steering from crowns, ruts, or pretty much anything unusual.
Went to change a lane........ZAP, 2 lanes over - scared the crap outta me

Mainly a function of wide tires and huge negative camber.

Sounds like your car is a track beast, similar to mine, and the behavior is just part of the price for this on-track performance
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Last edited by Craig 930 RS; 01-05-2009 at 07:21 PM..
Old 01-05-2009, 07:08 PM
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Thanks everyone for their input. It looks like the consensus is to bring the toe in and give it more negative camber across the board. This car is no longer a street car so tire wear around town is not an issue. It's been difficult wringing this thing out because of multiple changes done at the same time but I think we're on the right track. For now I'm going to leave the Bilstein Sports alone and just change the alignment settings. Once I get more seat time then maybe go to coil-overs. At this point I think it will be better to actually drive the car and gradually let it evolve. Last year at Road America (first time out there in 3 years with this car) I was afraid of the car and was not sure of its capabilities. I knew I was holding people up in the corners then hit the straights and they all disappeared. Poor BMW's. Just need to know the car and what it car do. Jeff
Old 01-06-2009, 08:20 AM
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Quote:
Originally Posted by kupcar View Post
Thanks everyone for their input. It looks like the consensus is to bring the toe in and give it more negative camber across the board. This car is no longer a street car so tire wear around town is not an issue. It's been difficult wringing this thing out because of multiple changes done at the same time but I think we're on the right track. For now I'm going to leave the Bilstein Sports alone and just change the alignment settings. Once I get more seat time then maybe go to coil-overs. At this point I think it will be better to actually drive the car and gradually let it evolve. Last year at Road America (first time out there in 3 years with this car) I was afraid of the car and was not sure of its capabilities. I knew I was holding people up in the corners then hit the straights and they all disappeared. Poor BMW's. Just need to know the car and what it car do. Jeff
What dates were you at RA since I go every year with the Chicago region either Labor Day or Memorial day weekend?
I had my silver 79 930 there over Labor Day and thought the track was wierd with all the over passes and bridges removed after Canada corner.
That region runs a great event......maybe see you there this summer.
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1979 930 Turbo....3.4L, 7.5to1 comp, SC cams, B&B intercooler, Snow Perf water/meth injection, Rarlyl8 headers, Garret GTX turbo, 36mm ported intakes, Innovate Auxbox/LM-1, custom Manually Adjustable wastegate housing (0.8-1.1bar),--running 0.7bar max
---"When you're racing it's life! Anything else either before or after, is just waiting"
Old 01-06-2009, 12:13 PM
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