Damn rear gets scary floaty
Thread Starter
Launching!
Joined: Aug 2002
Posts: 264
Likes: 0
From: Milwaukee
Rice Burner, absolutely right on all counts.
The problem is that sometimes, I don't have a choice but to let off the gas or even slam the brakes. Don't misunderstand me, I'm not tearing rubber everywhere I go, Just sometimes I'm in the middle of a turn, something happens and the rear starts dancing a jig. It's very scary at a high rate of speed, but even at a lower rate it is still there.
So my concern is getting this under control.
Samz28, I don't claim to have driven the best sports cars around , but the one before the Trans-Am was a Subaru SVX. Allwheel drive and independant suspension all around. It was more than a night and day difference going from that car to the Trans -Am.
At first I thought something was broken in the rear suspension. The car swayed side to side everytime I changed direction. It felt like the rear was attached by a rubber band, I always had to wait an extra moment for the rear to catch up to the rest of the car. I really think this is an unfortunate characteristic of a solid rear/ panhard set up.
Granted this is just my opinion, but when I got the SLP hard rubber bushings for the panhard,and had a llocal chassis shop box it, alot of the sway went away. Could be that if I go with a larger rear swaybar and harder bushings all around the rest of it will vanish
The problem is that sometimes, I don't have a choice but to let off the gas or even slam the brakes. Don't misunderstand me, I'm not tearing rubber everywhere I go, Just sometimes I'm in the middle of a turn, something happens and the rear starts dancing a jig. It's very scary at a high rate of speed, but even at a lower rate it is still there.
So my concern is getting this under control.
Samz28, I don't claim to have driven the best sports cars around , but the one before the Trans-Am was a Subaru SVX. Allwheel drive and independant suspension all around. It was more than a night and day difference going from that car to the Trans -Am.
At first I thought something was broken in the rear suspension. The car swayed side to side everytime I changed direction. It felt like the rear was attached by a rubber band, I always had to wait an extra moment for the rear to catch up to the rest of the car. I really think this is an unfortunate characteristic of a solid rear/ panhard set up.
Granted this is just my opinion, but when I got the SLP hard rubber bushings for the panhard,and had a llocal chassis shop box it, alot of the sway went away. Could be that if I go with a larger rear swaybar and harder bushings all around the rest of it will vanish
TECH Addict
Joined: Sep 2003
Posts: 2,065
Likes: 0
From: Atlanta, GA
i dunno. im new, im just asking ya guys what you think will help remove this problem? it's annoying. Maybe i'm asking too much from the archaic suspension? i can accept that answer.
(my other car is a suspensioned vw corrado fwd, and 2002 330ci, i used to have an 01 audi a4 quattro). The a4 handled the best, it lived for twisties, i understand this car isn't. But there's gotta be some things that can help.
I noticed the rear end twists alot as well. The bimmer brake stands into a perfect plant squat with no unibody twist nor "axle movement".
I dont expect z28 to behave like a sophisticated multipoint front/rear with independent, but was wondering what HELPED?
sorry to muck your racing thread up. My main concern is the throttle let off, and having to correct. It doesn't feel natural. Perhaps the nitto 555R's in the back?
(my other car is a suspensioned vw corrado fwd, and 2002 330ci, i used to have an 01 audi a4 quattro). The a4 handled the best, it lived for twisties, i understand this car isn't. But there's gotta be some things that can help.
I noticed the rear end twists alot as well. The bimmer brake stands into a perfect plant squat with no unibody twist nor "axle movement".
I dont expect z28 to behave like a sophisticated multipoint front/rear with independent, but was wondering what HELPED?
sorry to muck your racing thread up. My main concern is the throttle let off, and having to correct. It doesn't feel natural. Perhaps the nitto 555R's in the back?
Thread Starter
Launching!
Joined: Aug 2002
Posts: 264
Likes: 0
From: Milwaukee
Oh no! Your not messing anything up. This is exactly the issue I'm trying to resolve. Sorry if I came on strong, didn't mean to.
try a more solid panhard. I'm certain that U-shaped length of steel flexes and twists like a pretzel.
try a more solid panhard. I'm certain that U-shaped length of steel flexes and twists like a pretzel.
TECH Addict
Joined: Sep 2003
Posts: 2,065
Likes: 0
From: Atlanta, GA
okay i got a BMR setup coming hope it helps some out. I read up where they dis BMR's idea of parts, but oh well orders' shipped already.
I got the lower end parts:
LCA's non-adj
panhard non-adj with poly/rubber (should have got both poly?)
and strut bar.
I don't want to lower the car cause i've seen stock ride height cars with Longtubes and i'd rather not rip my exhaust apart all the time. Plus the wifey will be driving. I'm mostly concerned with her safety after the parts (in my sig) get put in the car is likely to be an animal (all parts go on next friday).
I'd like her to be able to safely drive the car. She drives the 2003 330ci coupe which i was talking about, it's f'ing graceful as can be for a RWD. Just don't want her to kill herself on a WOT passing move when the car has nearly 375whp and a stall in it.
I can handle driving it like a boat. But do you think running 28psi (to keep the insides of the nittos) in 245-50-16 might be lending some issue to this matter? When the crappy yoko a-509 (burnout city) were on, the car was a little tighter, so i can attribute something to the tires, but i think i'll stick with the 555R's since the bolt-on's would decimate the a509's and leave my wife in the forest/wrapped up in a pole.
Maybe i'll just have to teach her to drive again.
Do subframes help alot? welded seems to be the only way to go and they aren't that much $$. Maybe i should invest in them? Hows the rub factor on curbs and speed bumps with LT's and SFC's?
Lowering will never be an option, although it would probably help i spose.
do you guys with A4's and 'verters actually road race your cars? Doesn't get too sketchy on the course without at least tiptronic control ?
I got the lower end parts:
LCA's non-adj
panhard non-adj with poly/rubber (should have got both poly?)
and strut bar.
I don't want to lower the car cause i've seen stock ride height cars with Longtubes and i'd rather not rip my exhaust apart all the time. Plus the wifey will be driving. I'm mostly concerned with her safety after the parts (in my sig) get put in the car is likely to be an animal (all parts go on next friday).
I'd like her to be able to safely drive the car. She drives the 2003 330ci coupe which i was talking about, it's f'ing graceful as can be for a RWD. Just don't want her to kill herself on a WOT passing move when the car has nearly 375whp and a stall in it.
I can handle driving it like a boat. But do you think running 28psi (to keep the insides of the nittos) in 245-50-16 might be lending some issue to this matter? When the crappy yoko a-509 (burnout city) were on, the car was a little tighter, so i can attribute something to the tires, but i think i'll stick with the 555R's since the bolt-on's would decimate the a509's and leave my wife in the forest/wrapped up in a pole.
Maybe i'll just have to teach her to drive again.
Do subframes help alot? welded seems to be the only way to go and they aren't that much $$. Maybe i should invest in them? Hows the rub factor on curbs and speed bumps with LT's and SFC's?
Lowering will never be an option, although it would probably help i spose.
do you guys with A4's and 'verters actually road race your cars? Doesn't get too sketchy on the course without at least tiptronic control ?
Originally Posted by samz28
okay i got a BMR setup coming hope it helps some out. I read up where they dis BMR's idea of parts, but oh well orders' shipped already.
I got the lower end parts:
LCA's non-adj
panhard non-adj with poly/rubber (should have got both poly?)
and strut bar.
I got the lower end parts:
LCA's non-adj
panhard non-adj with poly/rubber (should have got both poly?)
and strut bar.
You very well might have traded the "flighty" or "floaty" feel when you unload the chassis. But, in my experience with poly bushings, it will now understeer something terrible, when you get on the gas after braking.
When the car is rolled over, like when cornering, the diff is still flat on the pavement. The LCAs are having to twist in their mounts. However, tube steal is very good at resisting twist. So ALL that force is transfered to the poly mounts. This force jams the poly bushing into the side of the cradle housing the LCA and creates a lot of friction or resistance to movement. This resistance translates into effective spring rate, which is inconsistant and unpredictable. There is no cure.
If the car is set up for good launch then the instant
center is getting biased toward brake hop or at least
lift. Brake or engine braking, same diff. To have both
worlds you would need two torque arms with decoupled
mounts (don't laugh, people do this, at least some crazy
ones). That way the arm that plants you right on accel
doesn't rob traction on decel & vice versa. The mount
is no longer captive but more like a snubber and the
braking arm may end up in a weird place... the pics I
saw were from an older A-body & the braking arm was
up under the axle arch and very short, while the accel
arm was much like ours except for the mount.
Not that this is likely to solve your problem, but food
for thought.
center is getting biased toward brake hop or at least
lift. Brake or engine braking, same diff. To have both
worlds you would need two torque arms with decoupled
mounts (don't laugh, people do this, at least some crazy
ones). That way the arm that plants you right on accel
doesn't rob traction on decel & vice versa. The mount
is no longer captive but more like a snubber and the
braking arm may end up in a weird place... the pics I
saw were from an older A-body & the braking arm was
up under the axle arch and very short, while the accel
arm was much like ours except for the mount.
Not that this is likely to solve your problem, but food
for thought.
Staging Lane
Joined: Nov 2003
Posts: 80
Likes: 0
I changed from Corvette to my current Z28.
At first I also thought that there was something wrong with the car.
The desert roads tha I was accustomed to driving at well over 100 in the Vette were a nightmare in the Z.
Started changing things to find out what the problem was.
As Herr Strano has already pointed out, it's the shocks.
I changed the Decarbons to DA Konis. Huge difference. At first I had to take 3 weeks to adjust them to what would suit my type of driving but once I got them straightened out it was a different car. Unbelievable. The rear end would stay in place, and was a lot more predictable.
Inherently, the only places where an independant rear end is better than a solid, is reacting to bumps in a broken road surface. This is a problem in my camaro that I have accepted and am willing to live with. The rest of sorting the suspension is a matter of physics and geometry.
FWIW, I also went to 275 tires.
At first I also thought that there was something wrong with the car.
The desert roads tha I was accustomed to driving at well over 100 in the Vette were a nightmare in the Z.
Started changing things to find out what the problem was.
As Herr Strano has already pointed out, it's the shocks.
I changed the Decarbons to DA Konis. Huge difference. At first I had to take 3 weeks to adjust them to what would suit my type of driving but once I got them straightened out it was a different car. Unbelievable. The rear end would stay in place, and was a lot more predictable.
Inherently, the only places where an independant rear end is better than a solid, is reacting to bumps in a broken road surface. This is a problem in my camaro that I have accepted and am willing to live with. The rest of sorting the suspension is a matter of physics and geometry.
FWIW, I also went to 275 tires.
I've noticed the same thing when accelerating through a curve and letting off to shift gears; you get a wiggle like the car doesn't know what direction it's going. I thought it was because I haven't installed rear LCA relocation brackets yet. I have Konis, big sway bars, and Pilot Sports on 18's.
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Originally Posted by Cal
I've noticed the same thing when accelerating through a curve and letting off to shift gears; you get a wiggle like the car doesn't know what direction it's going. I thought it was because I haven't installed rear LCA relocation brackets yet. I have Konis, big sway bars, and Pilot Sports on 18's.
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Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
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www.stranoparts.com --814-849-3450
Results matter. Talk is cheap. We are miles beyond the success anyone else has had with the 4th gens, and C5, C6, C7 Corvettes,
10 SCCA Solo National Championships, 2008 Driver of they Year, 2012 Driver of Eminence
13 SCCA Pro Solo Nationals Championships
2023 UMI King of the Mountain Champion
Maybe Sam will agree with me on this one.
Racing/Street driving dynamics 101:
Picture you car balanced on a fulcrum in the middle of the car. as you drive under steady throttle the car stays balanced on the fulcrum. As you accelerate the front picks up, as you brake/decelerate the rear lifts up. Now as you are going through a corner you now also add a "transient" into the picture, side loading the car. As you are going through the corner side loading the car and then lift on the throttle the car now dives on its nose while its side loaded. For the most part you just loaded the outside front tire with all of the work. And you have also taken away from the traction that the rear was providing you. If you were to stab the brakes rather than lift it will magnify this effect 10x's over. This is what makes the rear feel "light" or "dance around".
The best way to cure this is to go through the corner with a proper "set" and stay smooth on the throttle the entire way through. But in the real world this isnt always possible.
So to help reduce the amount of Body roll/brake dive a good set of shocks/springs and a good set of sway bars will HELP, not cure the problem. Even F1 cars still have to "fight" these issues. And one of the best mods you can do for your car is the "driver mod". this alone was the single best mod I have done to my car, all the rest was just icing on the cake. Going to a good driving school will VASTLY improve on your ability to handle a car even in adverse conditions.
Racing/Street driving dynamics 101:
Picture you car balanced on a fulcrum in the middle of the car. as you drive under steady throttle the car stays balanced on the fulcrum. As you accelerate the front picks up, as you brake/decelerate the rear lifts up. Now as you are going through a corner you now also add a "transient" into the picture, side loading the car. As you are going through the corner side loading the car and then lift on the throttle the car now dives on its nose while its side loaded. For the most part you just loaded the outside front tire with all of the work. And you have also taken away from the traction that the rear was providing you. If you were to stab the brakes rather than lift it will magnify this effect 10x's over. This is what makes the rear feel "light" or "dance around".
The best way to cure this is to go through the corner with a proper "set" and stay smooth on the throttle the entire way through. But in the real world this isnt always possible.
So to help reduce the amount of Body roll/brake dive a good set of shocks/springs and a good set of sway bars will HELP, not cure the problem. Even F1 cars still have to "fight" these issues. And one of the best mods you can do for your car is the "driver mod". this alone was the single best mod I have done to my car, all the rest was just icing on the cake. Going to a good driving school will VASTLY improve on your ability to handle a car even in adverse conditions.
Originally Posted by Sam Strano
Where are you shocks set? My guess is relatively soft. The wiggle is the body moving, more rebound will slow that down. That's one of a shock's primary jobs!
I tried that turn again on the way home from work tonight. It's a pretty low speed turn so not that dangerous to test on. This time I noticed that what I have is oversteer when I accelerate hard through the curve in 3rd gear. Then when I let off to shift to 4th, the oversteer suddenly disappears. Is this a normal fbody trait? Anyone else notice this behavior?
