Still having some oversteer

ikle

Active Member
I am thinking of swaping out my rear Kirban cargo springs for some Moog 5379 and replacing my rear Bilstein shocks to KYB to help with my oversteer issue. I know the Bilsteins are rated at 360 psi and KYB are rated at 280 psi which should help some. I can't find any info for the spring rating on the Kirban springs so I have know idea if the Moog 5379, with the load rating of 760 is a softer spring. Does anyone know ?
Thanks, Kyle.
 

ikle

Active Member
Can you expand on the "oversteer issue" you are having?

Sent from my SM-G930P using Tapatalk

Yes, when I go around a corner the rear end of the car wants to come around like a drift car, it feels a little unstable going into the corner but feels better if I accelerate mid corner to exit.

For suspension :
Front: Global West " Gplus" tubular uppers with their " Del-A-Lum " bushings in stock lower control arms with stock spindles with slightly taller lower ball joint. Kirban front springs with Hotchkis 1 3/8 hollow swaybar #2201f and Bilstein shocks with poly bushings on top.

Front end alignment:
Right caster +6 3/4 camber -1 1/4 toe in 1/32
Left caster +6 3/4 camber -1 3/8 toe in 1/32

Rear suspension :
Global West tubular upper and lower CA with their spherical bushings using rubber bushings in rear end housing. Kirban cargo springs with poly insulators, Bilstein shocks with DSE 1 1/8 swaybar set at softest setting. Maybe I should have gone with their 1" swaybar.

Body mounts all poly to eliminate the Buick " boaty" feeling

Front tires :
235/60/15 on stock GN rims with 3/16 spacer

Rear tires:
245/60/15 on stock GN rims

Tire pressure :
Front 32lbs
Rear 35.5 lbs

Thanks, Kyle.
 

ikle

Active Member
I don't know if this is possible but the problem started when I added the Poly body mounts to stiffen up the chassis. I also have behind the seat GNX body braces
 

ikle

Active Member
Have you tried lower the rear tires PSI to 32 also?

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No I haven't, I thought with oversteer the correction would be to raise rear tire pressure and/or lower front. I did have both set at 35psi before I lowered the front to 32psi. It seemed to handle slightly better with lower front tire pressure.
 

scot w.

GNSperformance.com
Disconnect the rear sway bar end links once and take it for a drive and see how it acts and let me know..
 

DeltaBravo

Retired U.S. Army/Navy
The problem with the link you provided...

It is geared towards Porsche's....Rear mounted engines....meaning the weight is in the rear, not the front.

I run 36psi in the rears and 30 in the front (which is common in the Porsche community) of my garage queen 1988 Porsche. They are entirely different animals than front engine cars.
 
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UNGN

Can't Re- Member
As people have said, lower The pressure in the rear or run taller tires in the rear (like 255s) to reduce oversteer.

On our 2+2 we increase rear tire pressure/lower front tire pressure to reduce understeer. 35 psi is a lot of tire pressure for handling with a wide tire on a skinny wheel. 28 psi in back should increase the contact patch size and help a lot.
 

1986 Buick GX1

GX1 #001 [The One and Only]
I've always read that the stiffest end of the car slide first.
In your case the rear slides first, meaning the rear is stiffer in relation than the front.
Softer rear springs, smaller rear sway bar or softer tires (less pressure) would help.

On to the other end of the car.
Stiffer front springs, bigger front sway bar or harder tires (more pressure) would achieve the same result.
I think shocks provide a comfort or performance ride, not contributing much to the front and rear balance. Just my thoughts.

If you're looking for a more "sport ride" (with the stiffer sway bars I figure this is your preference) maybe stiffer front springs would suit your tastes.

Springs are generally listed by spring rate (lbs/ in.). I think the load rating is more related to ride height.

Scot at GNS Performance has personal experience with auto X road racing type stuff and as well as other venders carries UMI Performance products, a very reasonably priced parts supplier.

For reference, the searches I've done suggests the stock GN spring rates are 420 lbs/ in. front and 120 lbs/ in. rear.

The informative posts from Scot and others convinced me to get the UMI 1" lowering springs (same height as worn out stock springs) which are rated 600 lbs/ in. front and 130lbs lbs/ in. rear.

I have the springs installed, but with other upgrades and life going on, I haven't had it on the road yet so I cannot comment on the ride.

Best of luck getting things sorted out.
 

UNGN

Can't Re- Member
You could take some negative camber out of the front. -.75 degrees is plenty with street tires and tall balljoints

I don't know how stiff the kirban cargo springs are, but you could swap in a stock pair and see if this cures it. that would be a cheap enough fix. A softer rear spring should help.
 

ikle

Active Member
Disconnect the rear sway bar end links once and take it for a drive and see how it acts and let me know..

Scot I haven't had time yet to disconnect the rear sway bar links, I appreciate your reply and I will report back my findings as soon as I have the time.
I was reading your post on the RideTechs " Street Grip " suspension upgrade, I noticed in the pics how the rear springs were installed, I installed my springs opposite of that in the pics and was wondering if this could cause my oversteer issue. Thanks, Kyle.
 

ikle

Active Member
Disconnect the rear sway bar end links once and take it for a drive and see how it acts and let me know..

Scot, today I disconnected the rear swaybar links and the car handled great, I was able to go though the corners about 5 mph faster than with it connected. The car oversteers ever so slightly that I think upgrading the rear tires from 245/60r15 to 255/60r15 should take care of it.

So what I have done to address my oversteer problem:
1) lowered rear tire pressure to 28lbs and raise front tire pressure to 35 lbs
2) replaced the variable rear springs to a softer consent rate Moog 5379 spring
3) disconnected rear swaybar links
4) thinking about going from 245/60r15 to 255/60r15 in the rear to help with the slight oversteer I am having now

So is this a good problem to have ?
Is using poly body mounts stiffen up the chassis that much that it prevents body roll when cornering ?

I am a little confused, can you explain this to me. Thanks for your help, Kyle.
 
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