Hey guys, the understeer in my 91 Trans Am WS6 (with pretty fresh Riken Raptor tires) is just killing me. It's very difficult to break the rear end loose in that car while corning (not on public roads though) so I was thinking of using a beefier rear sway bar. All it does right now is make the front tires scream and make it feel like the front wheels are gonna get torn off, regardless of what's done while driving. Is this how they handled from the factory, or is something possibly wrong with my car? What kind of sway bar would you recommend to give a more neutral feel yet still be safe to drive daily? Thanks!

 

I dealt with the exact same issues... A really good performance oriented alignment will help greatly with your issue. From the factory these cars are supposed to have POSITIVE camber (top of tire leaning outwards) by .5 degrees I found by making the camber negative more than the factory specs they tend to stick the front end to the ground a little better. You want your front tires to contact the ground very very flat while cornering for the best traction. I have a racing wheel alignment book kicking around somewhere... I will see if I can find it.

 

If you already have a WS6 car, it likely has a huge rear bar on it already. I doubt you need larger.

The alignment as mentioned above may make a huge difference. The positive camber & toe in tends to make the car understeer. This is desirable for people that cannot drive.... the front tires squeal, you turn-in more, scrubbing off speed & it eventually turns. Oversteer is not so forgiving to the novice & usually results in a trip to the body shop for quarter panel replacement.

For those that want the car to corner at its limits, you can go much more aggressive on the setup & make it turn. -.5 to -.75 camber on the street will not destroy tire life, but will make a big improvement. Caster will be typically as much as you can get equally on both sides. At least 4 to 4.5deg would be nice. About 1/16" toe in will be tire friendly, whereas toe out will help it turn in, but is rough on tires. There is some compromise if you do not want to eat the tires.



There could be other causes depending on the nature of understeer, meaning does it do this all the way through the turn, on initial turn in, or does it get worse mid way through the corner?

Typically anything the allows the rear inside corner to lift, or the outside front corner to dive will transfer additional weight to the front outside tire, causing it to slide.

Stiffer rear shocks (on extension) will improve turn-in by holding the weight to the rear, but it is all relative to the rest of the suspension setup.

Give us a list of your spring & shock combination, plus tire sizes & pressures to better help understand the problem.

 

My car is all stock with KYB GR-2 front struts (rebuilt front end too but with factory spec Moog parts). The rear shocks might still be the original ones from the factory; I haven't replaced em yet. And the tire size is the standard size that came on the 16" crosslace rims. I had the tires replaced in July and I had the car aligned as well so I'm assuming the shop just did the standard alignment to extend tire life. I'd like to adjust the front end to make it feel better and still save too much wear on the tires, like you guys mentioned.

As for the nature of the understeer, it feels barely ok on the initial turn in but after that it just scrubs through the rest of the turn.

I also heard that a wonderbar might help a little, any thoughts?

 

What tire pressures are you running?

Can you see the scrub on the outer edge of the tires?

Your rear shocks have a lot to do with handling.
Regardless you should get a good set of shocks even if your front end is still at fault.

Do you know which springs you bought, there are quite a few & they may not have given you the WS6 springs? You can measure the wire diameter of them to get an idea of the rates.

 

I think I'm running 35 PSI in the tires but I'll double check that tomorrow.

Yeah I can see the scrub on the outer edges of the front tires. And when I'm cornering on the road, I can hear noise coming from the front outside tire (while cornering to the right I hear the front left tire making a light howl), even when I'm not pulling any serious Gs. I'll try to post up a video of that, assuming I finally put my engine's top end back together and the weather clears up (snapped a thermostat housing bolt today )

I believe my rear shocks are still the same ones the car rolled off of the assembly line with so I'll definitely replace those sooner or later, probably with KYB GR-2s.

And I believe the springs are factory, I never touched em and it doesn't look like any of the previous owners did. I can double check the wire diameter though; what are the WS6 spring specs?

Thanks!

 

You need to slightly up your rear spring rate about 25-50 lbs on both sides.
Either new springs, or if you know someone in racing that will let you borrow a few spring rubbers temporarly to test just how much stiffer you need to go to balance the car at steady state. The more you increase a spring rate the more that individual tire gets weighted and will not grip as well. You have too much weight going over ontot he front outside spring.

Swaybars are a fine tunning tool. You need more than that adjustment if it is plowing as hard as you are describing.

You tire noise can be partial alignment specs and partial tire quality. Generally tire noise is the tire rolling over off the tread footprint from wither low pressure of poor alignment in both camber and toe settings. Generally a tire with too much toe out will make noise- I gauarantee thats not your case though. See what your tire max psi is and experiment trying that- if its 42psi max then run that and try a coirner hard to see how the noise is. If thats the case then you most likely need more negative camber or even a tad more caster to produce canber gain when turning the wheel.

What you are decriibing it nothing strange to a stock suspension car. In other words, nothing is wrong- thaty is typical of a stock car with factory specs. THey are not racecars and are set consevative to plow in an emergency situation so the car takes a hit directly head in rather than *** ending around. Many many things need to be changed to performance levels in order to get a racecar corner feel. Lots of geometry in suspension articulation will change whne dealing with stock componanats that flex both in bushing material and stamped steel levers.

You want performance levels, you will need to start buying and replacing factory stock compoinants. Check Spohn, Umi, Hotchkis, etc. Many many vendors out there.

Dean

 

Fix the shocks. The combination of new front struts and old tired rear shocks is an understeer contribution - the car starts out understeering during the transition from straight ahead to turning. This transition takes a little time; cornering isn't exactly a case of "either you are or you aren't".

Get a performance-oriented alignment. For general driving, I'd use Lonnie's specs, maybe with a tiny bit less toe (think 1/32" or even less, but still "toe in").

Once you get your alignment squared away, tinker with different tire pressures front vs rear. More than door sticker pressure up front, about 3 - 5 or 6 psi less in the rear. The higher pressure up front will make that end more responsive, and having less pressure in the rear will make the rear run at slightly higher slip angles (which is by definition a reduction in understeer effect). 37/33 is probably as good a place as any to start, but feel free to experiment with both pressures either higher or lower than that. If you find that you end up being a couple of psi under the door sticker pressure for the rears, you don't have to be too concerned so long as you don't normally carry a lot of weight in the car other than just the driver and maybe one passenger.

Then - no flame intended - concentrate on not overdriving. There is a limit to how fast you can make tires generate load, and it is possible to crank the steering wheel too fast for the driving conditions at hand. Especially if it's wet, or you enter a corner too hot, or if you're doing any braking at all (you aren't ready for trail-braking just yet; get however much braking is required all done in a straight line first). Once you make the outside front tire operate at too big of a slip angle, it'll plow, (usually) make lots of noise, and the steering will remain rather numb until you've slowed down enough for it to quit scrubbing sideways (or you've straightened out the wheel some if you've got enough road).

Plan on further tinkering with tire pressures as you learn to stay within the tires' limits.


Norm

 

Thanks for the tips guys! I'm looking for new rear shocks now. I'm thinking either KYB GR-2s or the gas-a-just shocks. I heard that the only difference is that the latter are a bit stiffer than the GR-2s. I'm not too concerned about ride quality (I doubt it could get much worse) so I think I might stick with the gas-a-justs. What would WS6-spec struts/shocks be? Were they different than the base model firebird? And considering the advice given, this should also help my understeer problem, right? Thanks!

http://www.summitracing.com/parts/KYB-KG5562/

And I just found the alignment sheet from the place I had my tires done. I'll post that up in a little bit.

And on a slightly different note, my front end (which is pretty new like I mentioned), makes an ugly groaning/creaking noise when I turn the wheel to lock or close to it when moving around slowly in a parking lot. It stopped for a little right after I rebuilt the front end but the noise came back. Everything is greased properly. I already asked this in a separate thread and I was told this was pretty normal but I just thought I'd double check.

 

Here's the alignment sheet:
The current specs are at the bottom, the top is right after I rebuilt it... I guess I was waaaaay off lol.



And the full size :

http://i751.photobucket.com/albums/x...Aalignment.jpg

 

I want to know what you changed in the rear of the car between alignments? If you changed nothing, then why are the #'s different. Looks to me that machine in not accurate.

I would take it to another shop. How in the world does an alignment tech send the car back to you with one of the perameters in the red. Your casters are wrong and your cambers could match in alot closer proximity- the tech was lazy and/or inept. That car has got to be pulling to the right.

What happened to these machines giving an SAI and IA readings? Its getting to be a dummied down world more and more every day.

 

Yeah I was wondering about that too, because I didn't touch the rear end. And these measurements were taken on the same day. I dropped the car off, they saw what the current alignment was (top), then they realigned it and measured again (bottom). I'll go to the shop shortly to show them because quite frankly, I didn't really know what I was looking at when I saw this paper when picking the car up.

And it doesn't pull to the right too much, but I noticed that I keep the wheel slightly turned a couple degrees to the left.

However I thought that caster isn't adjustable? What should the specs for that be?

 

I get a clear feeling that your alignment guy that day doesn't see many cars that he can't just do a "toe-n-go" job on. And when he has to do anything else, he gets sloppy.

He at least got the toes symmetrical, though I am still surprised that the numbers aren't more like +0.04° instead. But that camber is a bit ugly, and will tend to give you understeer. In addition, his cross-camber (side to side difference in cambers) is hardly any better than yours was. If you drive the corners very hard at all, all that positive camber is probably going to have you eating the outside shoulders of the front tires.




Norm

 

I don't doubt it, cause it was on the alignment machine for a while too! And there is visible scrub on the outsides of the tires like you mentioned Norm. I'll try to take a picture of that tomorrow.

So from my understanding, a good idea to help the under steer would be to ask for about -.5 to -.75 degrees camber and about 1/32" to 1/16" toe in? What about caster though? I thought it was non-adjustable. And any thoughts on the KYB gas-a-just shocks I'm thinking of getting?

 

Son of a b**ch! I just searched around about the caster issue and apparently it is adjustable! The jerkoff at the shop told me that he couldn't adjust it! I had a feeling something was up. Now I know.

 

Well I just dropped the car off at the alignment shop and of course I had to argue with them...
I called them to see what the deal was and they told me it was all set. I first asked for the guy there to tell me what the car was aligned to in order to save me a trip if I didn't like it. I didn't like it. Here's the first alignment done today:

http://i751.photobucket.com/albums/x...n/SCAN0003.jpg

After arguing about the caster setting, they took it back in and this is what it came out to be.

I have no idea how the toe has managed to change in between alignments (notice the different between the "current measurements" on the first page and the "before measurements" on the second page.)

http://i751.photobucket.com/albums/x...n/SCAN0002.jpg

The guy kept insisting that the caster was maxed out... he couldn't bring it in any lower (I asked for 4.5*). And despite my request of a little toe in, he said that he kept both wheels at 0* flat was because apparently some tire rod was wobbling when he was turning the clamp to adjust it (or some BS story like that). It was getting late and they told me I had 30 days to bring it back if I didn't like it so I just took the car back.

Well on the highway back home, the car seemed to have felt a little more planted than before at higher speeds. However I won't jump for joy yet because the highway I took was freshly paved and I didn't get a chance to drive on the rougher roads yet.

I stopped by the usual parking lot where I like to mess around with the car and I noticed A LOT less plow and the rear end actually kicked out pretty nicely when I stabbed the gas during a turn. It still felt very solid during an "emergency lane change maneuver," where I would stab the wheel left then back right (or vice versa) very suddenly at speed. That's with both my foot on and off the gas during the little test. It didn't feel like it was gonna spin out on me at all (and it didn't), which is a relief considering that the car is driven often. I still felt some under steer, and occasionally the tires would very briefly make that vibrating that I mentioned before. But it wasn't alarming. I'd like a little less plow, but I'm gonna drive the car some more before I jump to conclusions. I also heard a weird clunking coming from the back when the tail was whipping around. I'm thinking its just my spare tire bouncing around but I'll check that out tomorrow.

And I ordered a pair of KYB gas-a-just shocks yesterday, I wonder how that'll change the dynamics of the car. What do you think?

And I noticed another funny thing. Not sure if this is a coincidence or not but now the car squeals the rear tires when stabbing the gas from a standstill. Even with the rubber warm from me sliding around. It never did that before, which I just blamed on the 2.73 gears in the back. Strange... we'll see if it'll keep doing that tomorrow during the day when the pavement will be a little warmer.

 

ok just an FYI the thrust angle changing from 0.00 to 0.01 isnt that uncommon (some times it changes with front toe adjustments) . i do several alignments a day and i see that alot. those hunter machines are very very sensitive. and to be completely honest with you 0.01 degrees is a very very tiny amount. as for your caster issue.... the tech was lazy and didnt want to do it.... so ya you got screwed there. but dont freak out about the thrust angle thing, you wont notice a difference.



p.s. those alignment machines are so sensitive they can sense the earth moving. if you ever pay attention to the screen with the car sitting still the #'s change....

 

Absolutely.

At 0.01° resolution I'd think that even the effect of air currents in the shop against the targets could cause some scatter in the readings. You're counting on the targets not moving more than about 0.001" at the edges, and that's getting down almost to the level of conventional (non-CNC) machine shop accuracy.


muscle - 0.01° is about what 1/4 of 1/64" of toe amounts to, or what about 1/6 of one degree at the steering wheel will compensate for. You'll never notice. (Edit - I'll have to wait until later to see the photobucket pics to see what's there now.)


Norm

 

Oh I see. Sorry I was just a bit paranoid since I've been taken for a ride by shops a bit too often so I wasn't gonna take any crap from these guys. I honestly didn't think that those machines are THAT precise. Oh and the guys there told me the machine was new too.

The new KYB shocks that I ordered on Sunday night arrived today from Rock Auto. That's with the cheap shipping too!



I actually had some time and was able to install them fairly quickly today, and here are the old ones:



I was actually able to compress both by hand, one sprung back slowly and the other didn't as you can see. The new ones are rock hard in comparison. I'm thinking the old ones might be Gabriels judging by the red paint? I couldn't find a label; they were rusted so bad.

I was only able to take a 2 mile test drive but so far so good. I think I felt some less body roll on turns but it's too early to tell for certain.