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one of the great unwashed
 
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Suspension Upgrades and Camber

I just finished the suspension upgrades on my SC...I ripped it all out and started over. 21/27 bars, Bilstein sports, all new bushings, wheel bearings, turbo tie rods, rebuilt steering rack, etc. I bring it in on Wednesday for alignment and corner balance. I lowered the car to close to Euro height. The roll bars are the stock units, with new bushings.

I have been tweaking the weights and heights just to see the effects on ride and handling, to try and get a sense of cause and effect. Without a Hunter alignment machine and scales, there is only so much experimentation I can do. For example, if I raise the front end enough, I can get it to handle pretty much like the lawn tractor on wet grass.

This is 90% street car, I might take it to DE this year. The question I have is: Is there a practical setting for the camber considering the suspension modifications, or should I just use the factory settings, which I assume are a compromise of sorts anyway?

Thanks!
Pat
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Old 04-09-2005, 06:04 AM
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Alignment specs seem like asking for everyone's favorite Long Island Iced Tea receipe. You get everything from mildly spicy ice tea to instant oblivion.

My feeling is to use a performance-oriented set of specs. Most of our 911s are really weekend cars, not true daily drivers that do 10K miles/yr in all weather, so slightly uneven tire wear or sensitive handling isn't a problem.

FWIW, this is what I ended up with, after discussing w/ S-Car-Go. I told them the car was for AX/street. "Aligned to front -1.25 deg camber, very slightly toed-out (0" plus a smidge), 5-6% caster with a bit more on the right (to resist the crown of the road). Rear -1.5 deg camber, 1/16" toe-in. I asked for more negative camber [in front], but the shop said they couldn't get it without a shock tower strut and some more lowering."
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Old 04-09-2005, 07:06 AM
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cause and effect:

More front negative camber = more understeer/push, heavier steering. More performance?

Cheers,

Joe

Last edited by stlrj; 04-09-2005 at 08:10 AM..
Old 04-09-2005, 08:06 AM
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All else being equal ( big assumption here !)....running more camber in the rear will tend toward getting stabilizing understeer....running equal front/rear camber tends toward more neutral ..or even oversteering tendencies....

Wil
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Old 04-09-2005, 09:24 AM
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I have a similar set up on my SC with the exception of the bigger Carrera sway bars. The car is 2382 with a full tank of gas. I use my car mainly street as well and just had it corner balanced and ailignment. I took Steve at Johnson's Ailig suggestion of .75 in the front with 1.5 on the rear same toe as your talking about and the car has never handled better. It will probably wear tires faster but everything is a sacrafice one way or the other
steve
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Old 04-09-2005, 10:17 AM
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Thanks, all
As the car sits now, the alignment is "way out" of whack, but still roadworthy. However, it does understeer quite a bit. The oddity of this is that the understeer changes back to oversteer quite quickly, if that makes any sense to you. For instance, we've all seen racers "warm up" their tires by left-right-left...wiggling of their car. When I do that motion, the motion becomes amplified to the point of scary. It's hard to describe. It may be a mechanical lag from the sway bars transferring weight. I imagine this motion will dissipate when the car is aligned.
I'm going out to tweak some more with my homemade camber gauge.
By the way, I'll use the car whenever possible, except in the snow and when the salt is on the road. It's more fun to drive than my pickup. The only fair weather vehicle I have is the two wheeler.

Pat
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Old 04-09-2005, 11:56 AM
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Quote:
....running more camber in the rear will tend toward getting stabilizing understeer...
Meaning making the rear end looser to more closely match the looser front end that resulted from the increase in negative camber in front.

Reading between the lines you might notice that you will be increasing the sliding around effect of the rear to match the increased sliding effect of the front.

How's that for a performance increase!

Whatever happend to trying to get more bite out of your tires and suspension? Why are we always trying to turn our cars into surfboards?

Cheers,

Joe

Last edited by stlrj; 04-09-2005 at 12:06 PM..
Old 04-09-2005, 11:59 AM
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stlrj:

- My comment was meant to indicate what equal ( or unequal) front/ rear camber does to the basic understeering / oversteering characterisitcs of the car ...

You seem to imply more negative camber in the rear somehow makes it softer...or more prone to slide...in the rear... to now match the front. Wrong.

More rear camber will make the rear "stick" better in the back during turns ( relative to the less-cambered front)....simply a means to impart understeer. Having both front and rear camber equal...will either make the car neutral..or tend toward oversteer, depending upon the other set up items on the car.

Besides....what ever your "setup" is....it won't act the same for low speed ( high steering angle) turns...as it will for high speed ( small steering angle) turns. Buyer beware ! ....if you set up for neutral under low speed turns...you might end up with high pucker factor oversteer during high speed turns....not a good thing at all !!!

What are you talking about ! ?...... "how's that for a performance increase?". This doesn't necessarily imply wer'e dumbing-down our cars, in terms of performance potential. We're talking about things that can be done to balance the car.

Finally, what's that you say earlier?...running more negative camber in the front imparts more understeer??? Wanna rethink that ?

- Wil
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Last edited by Wil Ferch; 04-09-2005 at 12:54 PM..
Old 04-09-2005, 12:49 PM
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"Why are we always trying to turn our cars into surfboards?"

- because it is FUN!
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Old 04-09-2005, 01:12 PM
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After we get them to slide around so much we have to go auto-X school to learn how to drive them.
Old 04-09-2005, 02:29 PM
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Crap. Now I have to think again. Assuming the object is to maximize tire conact with the ground, which is probably what Porsche was thinking when they wrote the alignment specs, how much do I want to deviate from the specs? Bentley says 0 front, -1 rear. In a turn, the camber goes to relative positive on the outside tire, and relative negative on the inside (someone correct me if I'm wrong, please). With stiffer springs and sport shocks, I guess I'm limiting the travel in the vertical direction due to the bump of the shock, and the stiffer springs. Thus, I am decreasing the camber relative effects.

Cdnone1, I'm guessing your specs you stated are negative numbers? Otherwise, my theory just got shot.
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Old 04-09-2005, 05:38 PM
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Pat-

Here are a few alignment/corner balance threads to check out:

corner balance qestions
Leveling car: sway bars hooked up?
alignment settings
Old 04-09-2005, 06:11 PM
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Thanks, Eric
I guess you've done this before, huh?
Pat
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Old 04-09-2005, 06:38 PM
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Quote:
Originally posted by patkeefe
Crap. Now I have to think again. Assuming the object is to maximize tire conact with the ground, which is probably what Porsche was thinking when they wrote the alignment specs, how much do I want to deviate from the specs? Bentley says 0 front, -1 rear. In a turn, the camber goes to relative positive on the outside tire, and relative negative on the inside (someone correct me if I'm wrong, please). With stiffer springs and sport shocks, I guess I'm limiting the travel in the vertical direction due to the bump of the shock, and the stiffer springs. Thus, I am decreasing the camber relative effects.

Cdnone1, I'm guessing your specs you stated are negative numbers? Otherwise, my theory just got shot.
Couple of observations. Maybe I'm misinterpreting what you're saying, so if all this is obvious, forgive me. If your were building a drag racer, you'd want, at least theoretically, 0 camber. This maximizes the contact patch for straight line acceleration. If you're setting up a car to do AX or track, you want some negative camber. Thought experiment. Which can you corner faster on, a perfectly flat surface or a positively banked one? Negative camber gives you, in effect, artifical positive banking under corning load. As Wil correctly points out, more negative camber in the rear will help promote understeer because ther rear has more "banking" to overcome. So what we are dealing with when adding negative camber is a compromise between maximizing the contact patch during cornering versus (de)acceleration. One other important point to remember is that tires deform. Even if your spring rates were ultra-high and your suspension prevented any lean, which at the rates you're running isn't the case, the tires will flex under weight transfer.

On my 1970 with last seasons 22/32 TBs, custom bilsteins kokeln bars, I was running -1.75 in front, -2.0 in the rear. Pretty much the most I could get. The car took FTD a couple of times (except when that pesky Lotus 7 showed up) One thing that also should be pointed out is that certain tires, particularly Hoosiers, like a good deal of negative camber, generally more than a 911 can deliver without tower mods, or adjustable suspension pieces. If you intend to run them, get as much as you can, I know several non-Porsche AXers that are running -3.00 or there abouts. In my experience, the problem generally is that you can't get enough negative camber with yours and my previous suspension.
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Old 04-09-2005, 07:22 PM
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My understanding was that his intended use was 90% street meaning street tires and very occasional DE which factory alignment specs would be considered more than adequate.

My recommendations are based on my experience on the street/back country twisties with street tires where excessive amounts of negative camber in front and rear can adversly affect cornering capabilities.

I will admit that if I were creating a car more dedicated to DE it would included all the usual mods such as t-bars, braces, racing tires and a good amount of negative camber to be competative.

So for the street you might be better off staying closer to factory spec based on intended use.

Cheers,

Joe Garcia
Redwood PCA since 1976
74 911 3.2 transplant

Last edited by stlrj; 04-10-2005 at 06:33 AM..
Old 04-10-2005, 06:27 AM
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Yeah, 90% street use is indeed correct. I'm leaning towards an extra 1/2 degree negative on the front and rear, and see how that works out. I use it to commute to work, but we have lots of nice backroads here, which, fortunately, have golf courses strategically placed near them.
Pat
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Old 04-10-2005, 08:36 AM
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Pat...that's not a bad plan...factory specs plus another 1/2 degree ( i.e....additonal 30 minutes) camber both front and rear....

That should be a suitable compromise for the kind of use you intend....

Wil
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Old 04-10-2005, 11:31 AM
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