Figured out where the push is coming from
06-22-2009, 10:01 AM
#1
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Figured out where the push is coming from
When I contacted the previous owner of my GTS he said that DEVEK had done the suspension on the car, Hypercoil springs, Devek blue Front sway bar, rear sway bar, and Externally rebound adjustable Koni Reds.
I have been fighting push, and even more so since going from 225/285 tires to 235/275.
I have been trying everything I can adjust to get rid of push/understeer. Adjusting tire pressures, front swaybar stiffness, front and rear shock rebound.
Description of the understeer...In a steady state turn approaching the limit fronts start making noise and the car looses rotation. On lifting the throttle the noise and loss of rotation does not stop until the speed drops, as opposed to the weight transfer of lifting loosening the rear and rotating the car. If I floor the accelerator the car just understeers more instead of going into power oversteer. The only way I have been able to get the car to rotate is to pop the clutch to get the rear to break loose aka drifter style, which while it does get some rotation, it is not smooth at all, and none to fast neither. And no left foot braking did NOT help a bit. Just touching or tapping the brake pedal would cause even more understeer.
The balance I am looking for with a car with a near 50/50 balance is being able to maintain a slight 4 wheel drift through the corner using throttle to steer. By using the throttle to steer, I mean adding throttle causes a little understeer and the car goes a little straighter or turns less, lifting a little and the car rotates in or turns in more. To me this is driving at the limit of the traction of all four tires around the corner, where with the current understeer I am turning at the limit of just the front tires.
At the last autocross I attended the course had lots more tight twisty bits than usual really spotlighting my understeer, my times were abysmal. I got beat by .2 seconds by a GT3!
Anyway, upon closer inspection it looks like the car has the Devek Blue front sway bar, I don't know if this is the bigger of the two Devek bars or not. AND it has the stock rear sway bar. Too much front bar equals understeer!!!
By hitting the web sites of our 928 parts suppliers I found 928 Motorsports has a bracket that allows stiffening the rear bar by changing the drop link attachment location on the suspension for $75, and 928 Specialist has a stiffer adjustable rear bar for $225.
Just not sure which to go for. If I go for the replacement rear bar I am also considering adding the matching 928 specialist front bar instead of the blue Devek bar. I like the sliding adjustment of the Devek bar, but it does have some signs of the tires rubbing the paint off where it sticks out more than the bars with the 3 hole adjustment.
What do you guys think?
I have been fighting push, and even more so since going from 225/285 tires to 235/275.
I have been trying everything I can adjust to get rid of push/understeer. Adjusting tire pressures, front swaybar stiffness, front and rear shock rebound.
Description of the understeer...In a steady state turn approaching the limit fronts start making noise and the car looses rotation. On lifting the throttle the noise and loss of rotation does not stop until the speed drops, as opposed to the weight transfer of lifting loosening the rear and rotating the car. If I floor the accelerator the car just understeers more instead of going into power oversteer. The only way I have been able to get the car to rotate is to pop the clutch to get the rear to break loose aka drifter style, which while it does get some rotation, it is not smooth at all, and none to fast neither. And no left foot braking did NOT help a bit. Just touching or tapping the brake pedal would cause even more understeer.
The balance I am looking for with a car with a near 50/50 balance is being able to maintain a slight 4 wheel drift through the corner using throttle to steer. By using the throttle to steer, I mean adding throttle causes a little understeer and the car goes a little straighter or turns less, lifting a little and the car rotates in or turns in more. To me this is driving at the limit of the traction of all four tires around the corner, where with the current understeer I am turning at the limit of just the front tires.
At the last autocross I attended the course had lots more tight twisty bits than usual really spotlighting my understeer, my times were abysmal. I got beat by .2 seconds by a GT3!
Anyway, upon closer inspection it looks like the car has the Devek Blue front sway bar, I don't know if this is the bigger of the two Devek bars or not. AND it has the stock rear sway bar. Too much front bar equals understeer!!!
By hitting the web sites of our 928 parts suppliers I found 928 Motorsports has a bracket that allows stiffening the rear bar by changing the drop link attachment location on the suspension for $75, and 928 Specialist has a stiffer adjustable rear bar for $225.
Just not sure which to go for. If I go for the replacement rear bar I am also considering adding the matching 928 specialist front bar instead of the blue Devek bar. I like the sliding adjustment of the Devek bar, but it does have some signs of the tires rubbing the paint off where it sticks out more than the bars with the 3 hole adjustment.
What do you guys think?
06-22-2009, 10:16 AM
#2
Supercharged
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I had a similar situation, just not as sever as yours. I have the 928 Specialists adjustable front swaybar. It really stiffened up the front end, but also cause quite a bit of understeer. The supercharger allowed me to throttle-steer in corners, but was a bit too unpredictable so I decided to upgrade the rear swaybar with the 928 Specialists rear swaybar.
At first I had the rear WAY too stiff (used the middle hole) and the car would oversteer way too much. I decided to backoff the rear to the lower setting and now the car seems to be perfectly balanced. Going to SITM on some of the twisties, I had a few 4-wheel drifts and I could throttle steer if I wanted. The car feels perfect.
Oh, I have the Bilstein/Eibach setup on my car.
At first I had the rear WAY too stiff (used the middle hole) and the car would oversteer way too much. I decided to backoff the rear to the lower setting and now the car seems to be perfectly balanced. Going to SITM on some of the twisties, I had a few 4-wheel drifts and I could throttle steer if I wanted. The car feels perfect.
Oh, I have the Bilstein/Eibach setup on my car.
06-22-2009, 10:46 AM
#3
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Thread Starter
I understand the supercharger oversteer. With Michelin pilot sports I was able to throttle oversteer smooth enough to still get great times. However, when I went to these Dunlop Direnza Sport Z1 Star Spec tires, they have so much more stick throttle just goes forward without any spin unless I do a clutch drop or something really abrupt to break them loose. And like R compounds, once they break loose you got nothing to work with traction wise. Talk about unpredictable 
I'm surprised the these stickier tires are actually slower because of the loss of corner speed due to the unbalance they have brought to light.
Anyone used the 928 motorsports adjustable rear drop link mount with any success?
I'm surprised the these stickier tires are actually slower because of the loss of corner speed due to the unbalance they have brought to light.Anyone used the 928 motorsports adjustable rear drop link mount with any success?
06-22-2009, 11:05 AM
#4
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Roger also sells the Louie Drop Links that will stiffen up the rear.
06-22-2009, 11:06 AM
#5
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Okay, now I have 3 options. Oh yeah! In times past I did the Louie Drop Links on my 90 GT to balance out the Devek front bar. It was the red bar instead of the blue one and the drop links weren't quite enough, it was still a little pushy.
Anyone know the difference between the Devek Blue front sway bar and Red front sway bar besides the color.
Anyone know the difference between the Devek Blue front sway bar and Red front sway bar besides the color.
Last edited by RKD in OKC; 06-22-2009 at 11:22 AM.
06-22-2009, 11:19 AM
#6
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I'm no expert, but stiffening the front swaybar without also stiffening the rear sounds like a recipe for understeer-- you'll be cornering with one paw in the air like a 911. 
I have one data point to offer: We fitted a pair of Louie's rear drop-links to our 90GT Sat AM before the fun drive, and Zhowie!! Turn-in is crisper and the car feels very neutral in a corner, really nice. And it handled pretty great before (Eibach+Bilsteins, stock front/rear bars). Roger is selling Louie's links, there was a recent thread but I am not finding it (search is not my friend this morning).
Louie's links stiffen the rear bar by effectively shortening the upper radius by about 1.25" (starting from 9" IIRC). Carl's shorten the bottom radius, not sure by how much- it's a larger radius to start from.
Ideally you would want adjustable bars front and rear. But changing the rear bar is a nuisance. If the front bar is adjustable then a stiffer-but-fixed rear bar in combination with the adjustable front would be a good compromise, and Louie's links were certainly easy to fit- took about 10 min's.
Cheers,
I have one data point to offer: We fitted a pair of Louie's rear drop-links to our 90GT Sat AM before the fun drive, and Zhowie!! Turn-in is crisper and the car feels very neutral in a corner, really nice. And it handled pretty great before (Eibach+Bilsteins, stock front/rear bars). Roger is selling Louie's links, there was a recent thread but I am not finding it (search is not my friend this morning).
Louie's links stiffen the rear bar by effectively shortening the upper radius by about 1.25" (starting from 9" IIRC). Carl's shorten the bottom radius, not sure by how much- it's a larger radius to start from.
Ideally you would want adjustable bars front and rear. But changing the rear bar is a nuisance. If the front bar is adjustable then a stiffer-but-fixed rear bar in combination with the adjustable front would be a good compromise, and Louie's links were certainly easy to fit- took about 10 min's.
Cheers,
06-22-2009, 12:47 PM
#7
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Richard,
The "red" bar you refer to on our old 90GT was purchased used from David Roberts at 928 Specialists. I had Dumont install it for me.
IIRC, Dave didn't like the blue color that Devek painted their bars, so he repainted it red. Afterward, he had tire rub issues with some wider fronts he was running, so he took it off and sold it to me.
I believe it was Devek's standard bar, not their heavy duty model. This would probably explain why neither one of us tore out the mounts with it, as the HD version had a propensity to do. Maybe Dave will see this and chime in with his recollection.
HTH,
Jarrod
The "red" bar you refer to on our old 90GT was purchased used from David Roberts at 928 Specialists. I had Dumont install it for me.
IIRC, Dave didn't like the blue color that Devek painted their bars, so he repainted it red. Afterward, he had tire rub issues with some wider fronts he was running, so he took it off and sold it to me.
I believe it was Devek's standard bar, not their heavy duty model. This would probably explain why neither one of us tore out the mounts with it, as the HD version had a propensity to do. Maybe Dave will see this and chime in with his recollection.
HTH,
Jarrod
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06-22-2009, 01:49 PM
#8
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Thanks Jarrod, Cool, maybe the drop links will get this thing somewhere near balanced without too much effort. They got the GT pretty close when I added them to it. I was afraid it was the bigger Devek bar and the drop links wouldn't add enough to get the rears within the adjustable range of the front bar.
Jim, the previous owner that had Devek do the suspension told me the rear bar was not stock, but it sure looks stock, is the same diameter as stock (22mm) and is not adjustable like the stiffer rear bars I see available now. I guessing that whatever they are, the drop links will firm them up some and at least that will make some sort of difference.
Since it is looking like even the adjustable rear bars are adjustable in steps, ie., 3 holes, I am kinda liking the sliding adjustment of the Devek front bar for fine tuning. Like I mentioned in my first post, I am not just trying to firm up the handling for the street and twisty roads as much as tuning for a specific balance for optimal cornering at the limits in a slight 4 wheel drift. I would really like to give that Mustang Super Snake and Cobra Daytona replica a run for their money in my luxo 928. With all this push the closest I can get in the last 2 autocrosses is 2.5 seconds.
Jim, the previous owner that had Devek do the suspension told me the rear bar was not stock, but it sure looks stock, is the same diameter as stock (22mm) and is not adjustable like the stiffer rear bars I see available now. I guessing that whatever they are, the drop links will firm them up some and at least that will make some sort of difference.
Since it is looking like even the adjustable rear bars are adjustable in steps, ie., 3 holes, I am kinda liking the sliding adjustment of the Devek front bar for fine tuning. Like I mentioned in my first post, I am not just trying to firm up the handling for the street and twisty roads as much as tuning for a specific balance for optimal cornering at the limits in a slight 4 wheel drift. I would really like to give that Mustang Super Snake and Cobra Daytona replica a run for their money in my luxo 928. With all this push the closest I can get in the last 2 autocrosses is 2.5 seconds.
06-22-2009, 01:59 PM
#9
Nordschleife Master
try the ott drop links first,
Get the 928 motorsports adjustable point. but it is only really good for the tie down point. The andjustment points dont seem to have much of a difference.
if the ott drop links dont give you enough of what you need try to get the specialists bar. But AFAIK they are not availible.
Get the 928 motorsports adjustable point. but it is only really good for the tie down point. The andjustment points dont seem to have much of a difference.
if the ott drop links dont give you enough of what you need try to get the specialists bar. But AFAIK they are not availible.
06-22-2009, 02:12 PM
#11
Nordschleife Master
Do the specialists have the bars (front and rear) availible again????
As well, I wouldnt bother trying to use the website for ordering. I have tried it a couple times and it never works.
As well, I wouldnt bother trying to use the website for ordering. I have tried it a couple times and it never works.
06-22-2009, 02:51 PM
#12
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06-22-2009, 02:53 PM
#13
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Just heard no drop links and no rear sway bars currently available. I got three weeks before my next event. Sure hope I can get something by then!
06-22-2009, 03:12 PM
#14
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try the ott drop links first,
Get the 928 motorsports adjustable point. but it is only really good for the tie down point. The andjustment points dont seem to have much of a difference.
if the ott drop links dont give you enough of what you need try to get the specialists bar. But AFAIK they are not availible.
Get the 928 motorsports adjustable point. but it is only really good for the tie down point. The andjustment points dont seem to have much of a difference.
if the ott drop links dont give you enough of what you need try to get the specialists bar. But AFAIK they are not availible.
Of course they don't ! They don't alter the length of the "lever" therefore no change in force. The Ott's drop links do and they work !!!
Jan
06-22-2009, 08:40 PM
#15
Race Director
RKD
I have the 928motorsports adjustable rear sway bar mount + tie downs on the widow...right now I am running stock sways front and rear with the rear set to the 2nd stiffest setting and I like it.....plenty of turn, but not loose either.....I do think I might find some understeer once I up my pace a bit, mostly due to the 40mm wider rear tires...... Currently I have the stock drop links, but do have a set of adjustable Ott links for the rear too if I need even more stiffness....
I have the 928motorsports adjustable rear sway bar mount + tie downs on the widow...right now I am running stock sways front and rear with the rear set to the 2nd stiffest setting and I like it.....plenty of turn, but not loose either.....I do think I might find some understeer once I up my pace a bit, mostly due to the 40mm wider rear tires...... Currently I have the stock drop links, but do have a set of adjustable Ott links for the rear too if I need even more stiffness....