993 Alignment question
#16
Addict
Rennlist Member
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I learned a ton from Chris back when I was building and racing 993s. He was not my only mentor but he is a great driver, engineer and mechanic and really knew the 993 platform. I do hope it helps some folks. When these cars are set up right, they are truly a joy to drive.
Hank
Hank
#17
Three Wheelin'
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Thanks for posting that Hank, I did look up the original thread and it has a ton of info. The information that Chris posted about the sway bars, answers a question that I have had for a few years now. Thanks again.
#19
Nordschleife Master
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Sorry when I say quite lower offset I mean 16 in the rear. I' have very wide arches and using 930 Fuchs wheels.
Stealth, coincidentally my car is a 993 C4 with RS suspension specs. I copied RS geometry specs but car always understeer a lot, I trailbraking quite good but impossible to make it rotate quickly and I don't want to stiff the rear anti-roll bar which produces much of the effects that you described!.
Thanks guys for your quick and help.
David
Stealth, coincidentally my car is a 993 C4 with RS suspension specs. I copied RS geometry specs but car always understeer a lot, I trailbraking quite good but impossible to make it rotate quickly and I don't want to stiff the rear anti-roll bar which produces much of the effects that you described!.
Thanks guys for your quick and help.
David
Rs is a good start, try running less toe, run higher rear tire pressure, get a lot of front camber. My car (95 C4) is my Auto-X car, & this year I'm undefeated, routinely beat Gt3's. I have almost no understeer, & can have the back end come out when I want. I do have a little low speed tight turning understeer, dabbing the brakes helps as you turn.
What I found with the C4, go into a turn hard, & fast, brake heavy as you turn in, as soon as the suspension sets, roll onto the gas & stay on it as you exit. I'm usually WOT right before the apex.
My specs..
Factory M030 car with LSD, ROW M030 shocks/springs, US M030 bars, RS strut brace, Walrod bushings, 18in TT wheels 225/265 Yoko AD08 rubber.
ROW ride height, 1.25 all round camber, 0 toe F/R, lots of caster, 34 psi front pressure, 38psi rear pressure.
From my last auto-X, came in 1st in class, by over 1.5 sec.
#23
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Sorry when I say quite lower offset I mean 16 in the rear. I' have very wide arches and using 930 Fuchs wheels.
Stealth, coincidentally my car is a 993 C4 with RS suspension specs. I copied RS geometry specs but car always understeer a lot, I trailbraking quite good but impossible to make it rotate quickly and I don't want to stiff the rear anti-roll bar which produces much of the effects that you described!.
Thanks guys for your quick and help.
David
Stealth, coincidentally my car is a 993 C4 with RS suspension specs. I copied RS geometry specs but car always understeer a lot, I trailbraking quite good but impossible to make it rotate quickly and I don't want to stiff the rear anti-roll bar which produces much of the effects that you described!.
Thanks guys for your quick and help.
David
if you are using really low ET front wheels you have dramatically changed the geometry of the steering, your instant centers and scrub radius are nowhere near where they would need to be for best handling.
The GT2 EVOs use the outer holes for the side members to maintain reasonable scrub radius and instant center positioning. Then they use 10x18 ET32 245/645 tires & 11x18 ET14 325/680 tires to fill the wheel wells
alignment depends on the tire, for Pirelli
front
ground clearance 96mm
toe -5' total
camber -4* 10' each side
caster 4*30' max same both sides
rear
ground clearance 93mm
toe -35' total
camber -3* 45' each side
caster 3.5* max same both sides
camber
#25
Racer
Thread Starter
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I compare Caster to the angle of the head-set on the front of a bicycle: More angle means more stability and resistance to turning the front wheel.
Touring bike: Pronounced angle and long wheel base.
Racing bike: Less angle and short wheel base, criteria frame.
My 911 without power steering shows Caster as 6*5' in the manual for good self-centering and when Caster is reduced, steering is more responsive but also slower self-centering.
How is it that the Caster for 993 with power steering is less than for the older 911 without power steering?
#26
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generally speaking for most users most of the time, yes
correct
caster doesn't not exist in a vacuum, the entire front end of the 964 was redesigned from the 911, for instance scrub radius was changed from (+) to (-) caster and camber were both reduced and p/s added. The design goal for the 993 was to enhance the sporting feel so steering was quickened over 964, scrub radius increased to -10mm, caster increased to 5*20', track widened by 25mm, camber increased to -20', stiffer steering arm bushes, less toe, quicker steering rack. All these changes add up to fulfill the design goal of sportier handling but still w/ the stability expected at speed. The RS received a slower steering rack to enhance it perceived higher top speed steadiness though I've never had issues even on extremely long straights such as at Monticello.
My 911 without power steering shows Caster as 6*5' in the manual for good self-centering and when Caster is reduced, steering is more responsive but also slower self-centering.
How is it that the Caster for 993 with power steering is less than for the older 911 without power steering?
How is it that the Caster for 993 with power steering is less than for the older 911 without power steering?