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Way too understear on track

Had my car on track a couple of weeks ago, and felt it was too understear.
Front was just pushing too much out.

Previous owner has installed 24mm torsion bar front and 29mm rear. There is also coilovers with "helper springs"

According to this table 24/29 would result in really understear.



Is is possible to adjust the helper spings to make it stiffer in the rear to get less understear?
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 08-24-2011, 01:28 PM
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YES more spring / swaybar in the rear will make less understeer.

I run 22/31 bars on my car and its about neutral with this, but I have a tarrett adjustable sway in the rear so I can adjust it to slightly over/under steer.

I would try to bump up the springrate in the rear to start with for sure.

Last edited by zeb930; 08-24-2011 at 02:05 PM..
Old 08-24-2011, 01:46 PM
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BUT i think that because you got the biggest bars possible in the front the helper springs will probably be so stiff that reinforcement of the rear shocktowers will be preferable.

If you dont want to mess with the body it will be better to run smaller front torsionbars maybe 21-22..
Old 08-24-2011, 01:53 PM
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If there's room to move the camber plates and tops of the struts inward toward each other it will give you a little more negative camber on the front wheels and that will also help reduce understeeer.

The one time I had mine on a track it was at night in february and it was around 50 degrees out.
Fantastic for turbo boost and intercoolers but during the first lap on cold tires there was alot of understeer and by the second lap there was more lateral grip from the front tires as some heat got into them.
Old 08-24-2011, 02:56 PM
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What size tires? Tire pressures? Alignment?

But first glance is that the front TB are way too big. How heavy is the car?
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Old 08-24-2011, 03:00 PM
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With out proper alignment specs and or tire temperatures, I can only offer speculation.

Too many variables, tire pressure, sway bars (adjustable), ride height, corner weight, camber, toe and the list goes on.
Old 08-24-2011, 05:21 PM
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According to the table the fronts are 189% stiffer than stock and the rear 55% stiffer+helpers so however you look at it the front is MUCH stiffer.

Are you comfortable with the front stiffness? Then stiffen up the rear and vice versa.

I see 3 solutions to get a decently balanced car to work with(camber,tires,alignment etc)

1. Keep 24 bars and add 33 rear+helpers (last example in the table) (About 190% stiffer all round against stock/ If your helpers add around 30%?)

2. Keep 24 bars and 29 rear and add 135% trough heavy helpers to get same balance as above (will strain the shocktowers but may be ok, safer to reinforce)

3. Add 21-22 front bar and run 29+helpers (This will give a car thats about 70-100% stiffer than stock)

Or you run as is and have a super stable highway missile..
Old 08-24-2011, 05:58 PM
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My plan is to stiffen the rear towers during winter.
I think I was running tire pressure at 24 psi on Goodyear Eagle F1 GS-D3 tires

Will probably change for 21-22 in front.

Going to track next weekend, and will try the Khumo track tires.

What tire pressure are you running on track?
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1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 08-25-2011, 12:33 AM
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You can add more tire pressure to the rear. You can also try to change how you drive. Take more speed out before the turns and shoot for max speed in the straights or maybe even trail brake in to the turn to help the car rotate but there is the risk of getting the hammer efect and spinning in trail braking.
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Old 08-25-2011, 01:15 AM
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Tire pressure, really depends on how the car is set up. Do you have a pyrometer?

They are cheap, but give you a wealth of information on what the car is doing.
Rebco 290-8730 - Rebco Single Display Tire Pyrometers - Overview - SummitRacing.com

Also a good tire sheet will help.




Changing spring rates and sway bars without getting tire temps is a guessing game without knowing alignment specs. You could have a toe out issue, too much positive or negative camber in the front end, mis-adjusted swaybar in the front or rear. Or it could be your driving style.
Old 08-25-2011, 01:55 AM
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I would find a good P shop and have them do a suspension setup based on your car usage, street with some track, street/track, track/but streetable, etc. They're all trade offs. Then use that as a starting point for further mods.
I use to run the GS/D3's on our race car at track days when the track was wet. They are a great dry track day tire, and surprising good in the wet.
Going to a track tire just means you'll get into trouble at a higher speed.
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Old 08-25-2011, 07:05 AM
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Thanks guys.

Will going to have a wheel adjustment/setup at local Porsche shop, but will not make it before next Porsche track day.
Is there a way to adjust sway bars for less understear?

I have a TRG 22mm adjustable front sway bar and Weltmeister rear adjustable 24mm sway bar
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Trond R.
1979 930: Garret GT35r turbo, EFI, carerra intake, Link EMS, custom GT2 cams, 98mm JE P/C, 964 crank (stroker), custom valves & ported (XtremeCylinderHeads) etc..etc..
1972 914-6 GT replica project
1986 944 Turbo
Old 08-25-2011, 08:04 AM
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My .02. Stay with the GS/D3. Do a search and see what tire pressure folks are running with these tires. You say 24 lbs, is that hot or cold. Check the tire pressure as soon as you come off the track. Once you have the proper tire pressure, adjusting the pressure is the same as small sway bar adjustments. I would set both sway bars in the middle as a start point, then adjust from there. According to the Smart Racing sway bar instructions adjusting the front or rear bar is based on whether the car is under/over steering going into or coming out of a corner, don't remember which.
Your car may be so far out of adjustment that none of the stuff mentioned above does much, if anything.
If you want to take things further invest in a digital protractor to check camber, and either make or buy a set of Smart Strings to check toe and squareness. Check and record the suspension set up when you get it back from the shop as a future reference, also to check their work. I've had the unfortunate experience of having a couple different shops botch my suspension set up, so I started doing it my self.
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Old 08-25-2011, 08:37 AM
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If your spring rates are too far out no tuning of the sway bars is gonna correct your problem.
You need to decrease that front torsion bar diameter to get the spring rate down to what others have already suggested. You want to increase the factory rates approximately equally so figure out how track oriented you want to make things and get a value over stock first. For example I went about 80% stiffer as a target than original t-bars because I still drive on the street. So I ordered both new t-bars springs that got as close to that value as possible.
I run 22 frt 31 rear hollow bars on my 79 930 turbo and it is very neutral or slightly towards understeer. I can fine tune with the sways and at low speeds it still understeers which in large part the LSD diff causes as well.
After your all done lower the car to get the CG down and corner balance it. Alignment is another ball of wax, but in my opinion run as much neg front camber as possible for track days.
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Last edited by fredmeister; 08-25-2011 at 08:54 AM..
Old 08-25-2011, 08:51 AM
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Set the front one softer - longer arm; and the rear one stiffer - short arm - do some "testing" and start from there, shortening the front ones 1/2" at a time until you get the setting you're looking for. Then, do the same for the rear, from stiff to soft... there'll be a "better feel" you'll see.
Old 08-25-2011, 05:23 PM
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Quote:
Originally Posted by totle View Post
My plan is to stiffen the rear towers during winter.
I think I was running tire pressure at 24 psi on Goodyear Eagle F1 GS-D3 tires

Will probably change for 21-22 in front.

Going to track next weekend, and will try the Khumo track tires.

What tire pressure are you running on track?
If you run 21-22 in the front with 29 rear+helpers i think you will manage without reinforcing the towers (but it wont hurt to do it and you will be able to run the 24s with heavy rear helpers to match the front, if you want a stiffer set-up later on)

I run 30-32 psi front and 34-36 rear hot pressure with Toyo R888 235/295.
Old 08-25-2011, 06:43 PM
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