Pablo

iTrader: (1)

I didn't know that was a possible combination James, thanks for the info.

SlickTrackGod

I was going to ask if that wobble felt like the nose of the car- you already answered that.

It is you SAI is way out of wack and the car is fighting coming off it and centering itself on the road. now that the rear is planted, the diagonal transition from the inside rear is putting more of a push pressure on the outside front tire straining the load on it and making the car bobble as you apply throttle. Best way I can discribe it is it is like a bad wheel on a shpping cart that has the caster out of wack, the wheel bobbles about and does not track straight at certain angles of movement. This is a tough one to explain, I could show you in person with hands and words much easier.

SAI will also cause a car to pull one side or the other under braking if the sides are not equal- you feel the steering wheel fighting you.

hellz_wings

iTrader: (2)

I actually think I understand what you mean by that, and it's my gf that usually does the groceries lol.

But yes, SAI is messed up and the strut bolts will need to be turned to the outside , pushing the spindle away as much as possible, and then I'll bring the strut mounts back in, bringing the alignment back to negative around -1*. I'll also aim to get this equal so that it does not pull when braking at speed or will pull less in ruts or uneven roads. Mix high speed breaking, bumps, and/or uneven road together and I find myself getting a shoulder workout. On smooth pavement it's almost non-existent.

Just ordered a replacement outer tie rod adjuster from Spohn to replace the bent one. It was 18$ plus shipping. Phew that wasn't too bad lol.

SlickTrackGod

The pivot point #1 and the weight point #2 on the outside front tire are different. As you apply throttle and the wheel is turned still, the outer edge of the tire is catching grip and then releasing- think of it like a rear locker with the inside wheel skipping so to speak- yet when on the front and pushed agaist it will bobble rather than skip. It ideally is skipping on the tire slip angle.

You have to get the pivot point more closer to center of the tire tread laterally. Caster puts the lead in it so it tracks, SAI is kind the same for centering the side to side where as Caster at 0* centers the for and aft. Now you put the dimension of Camber into it and the wil not lift the inside front as much making the inside rear to transmit crossweight diagonally to the outside front on a turn weighting the faulty pivot. (In other words, you pushing on a bad shopping cart wheel with alot of weight on it)

Your SAI depends on your tire centerline- but keep in mind you need to keep within track width design of the steering geometry (ie ackerman). You start putting really wide track onto the car (like Pablos car for instance) and then you change the SAI to meet the wider track width centerline, your Ackerman now slows on tighter corners- you thus have to Toe out even more for race track alignment specs to get the car to turn in better on tight courses, but would really suffer in high speed straight line driving. Sometimes keeping the SAI low on wide, low slip angle race tires is better so the inside tire drags a bit more helping the car to rotate (like Pablos car again). This would ultimately hurt though on long duration races with lots more tire wear.

A little more SAI is good, too much starts to get bad again. A little more helps promote positive camber on the inside front wheel- but too much as stated with really wider tires will need a proAckerman adjustment so you are tracking or even dragging the inside tire and promoting a greater slip angle like the outside tire does. Most race chassis are purposely built without any Ackerman at all knowing the cars generally run wide race tires at speed which dynamically build Ackerman through slip angles or the tire- but suffer slow speed cornering especially if a grocery getter in a parking lot


These settings are really build specific with an intended type of tire. Testing can only be done on a skidpad with a pyro reading tire temps only after cornering at different constant speed tests and comparing temps accross the width of the tire to see how it is gripping. I own a pyro and did this to my car with the GSd3's on it. You also have to taylor the rear slip angles via roll overster/roll understeer settings of the LCA angles both static and dynamic....- yes it gets very very complex and will make your head hurt. I was able to get alot of heat in my inside radius tires compared to my outside tires. A stiff chassis is required, the more grippy the tire- the stiffer the chassis is needed.

edit: I will also add that keep in mind the SAI settings are not very sensitive to feel when smae adjustments are made. You will probably not even notice. This is more of a aid to inside tire grip whichis the minimal of the two (meaning the 2 sides of the car- outside and inside radius') As we all know without any education, the outside ties will always take the major blunt of conering loads. What we are tring to do is get a little bit of that shifted to the inside tires. It would probably translate into tens of a second in laptimes where as so many other settings are ALOT more noticable. the old saying, every bit counts and all the tenths add up.

edit#2- getting heat into the inside rear involves yawing the roll axis- thats a whole other novel and partially why I ran progressive rate rear springs on a solid axle car.

83 Crossfire TA

iTrader: (2)

I'm stumped what's SAI?

SCCAjunkie

Steering angle inclination. Draw an imaginary line through the top of the strut and down through the ball joint (in strut cars- go through both ball joints in double A-arm cars). It's the angle of that imaginary pivot line.

Where that imaginary line intersects the ground, compared to an imaginary vertical line through the centerline of the wheel/tire, is what determines scrub radius (or kingpin offset for the old-timers...). This is one of the major factors, along with caster, that determine steering "feel".

hellz_wings

iTrader: (2)

Update: Tried to do a some doughnuts in a parking lot and i couldn't break the rear loose even at full throttle! It just had eternal grip lol... I have a feeling there might be more understeer bias in the car at this point.. Still going to continue testing!

83 Crossfire TA

iTrader: (2)

Oh, why didn't you say so?


Actually I would have been OK with it if it was spelled out (as I've mentioned in a few places here, my wife just had twins, they're exactly a month old right now. I haven't slept for, well a month...)

I've always wondered about it on our cars and have never seen a good discussion of it. I wish I was able to tinker with it but haven't, but have always felt that with a larger, wider front tire and wider front track that more would be better (push the top bolt on the spindle out as far as it will go, bottom as far in, within the limits of the slop in the holes), but don't know for sure.

hellz_wings

iTrader: (2)

I have adjustable bolts on both holes of the spindle/strut assembly. I would assume that turning both bolts so that the tabs face outwards will push the spindle outwards (increasing positive camber and increasing IA). Then by adjusting the strut mounts, I would bring the camber back negatively (say, to -1*) which in increase SAI, and decrease positive scrub radius. I'm just hoping I'll have enough adjustment up top with the J&M (hotpart) camber plates to bring the camber back to negative -1*.. I would settle from anywhere between -0.75* to -1*).

SCCAjunkie

Sorry, I'm a teacher, so I have a habit of going into more detailed explanations than is necessary. I work part-time at a tire shop, right next to the alignment rack, and the alignment tech hates when I start talking to customers about alignments and specs. That's ok though, because he just throws wrenches at me when no one else is around. You could do the same...

I'm actually going to start a new thread to discuss SAI, kingpin offset, and scrub radius, so that we don't take this thread further off than we already have. I'm hoping you guys can give me some f-body specific info, and we can discuss the effects of those settings.

hellz_wings

iTrader: (2)

And that thread can be found here: https://www.thirdgen.org/forums/susp...rub-other.html

Moving back to topic: Braking. From my testing, I've found that trying to slam on the brakes when at high speed results in a smooth slowdown, but an inability to lock-up the front brakes.. Dean, I know you spoke about how your car's braking was affected, do you know what the reason for this is?

Pablo

iTrader: (1)

Did you properly bed your brake pads and is your system properly bled?

I have no problem locking up my brakes and I have a very low phb + huge sticky tires + stock brakes with a adj. prop valve.

Without properly bedding the pads you will have problems.
I don't see how the PHB height can affect braking except perhaps slightly under trail braking. And then I would say you could theoretically dial in more rear bias to compensate.

SlickTrackGod

I never had a problen loosing front brake pressure- that was not the purpose of my comment.

The brake benefit deals with the rear brakes being able to use more bias due to the car not cantelevering over onto the outside front tire and lifting the inside rear as much into and trough steady stat of cornering as well as just the simple striaght line articulation leverage gain of the rear swaybar to keep both tires following the road

hellz_wings

iTrader: (2)

Maybe that's why I felt as if it braked less? I have rear aluminum drum brakes in the rear and LS1 brakes in the front. Moving the bias to the rear would mean it's "using" the rear brakes more somewhat? Obviously the front LS1's are a million times better than the rear brakes and this is what caused the fronts not to lock up at speed.. Maybe it's time for LS1 rear discs and an adjustable proportioning valve lol..

Atilla the Fun

I can't see how towering the panhard is going to help, unless the car gets lowered the same amount. As for the 24 mm rear bar, I just went out and measured my '84 WS6 Trans Am, got 23.52 mm. I expect the '84 Z24 should have the 24 mm rear bar also.

Pablo

iTrader: (1)

Well you haven't done much research. Hit up google.

Atilla the Fun

It's not that I don't understand it. I do great with geometry, spatial relations, instant centers, et cetera. It's that it's not really changing the rear roll center height, it's merely getting the rear center of gravity slightly lower. If you want to change the roll center, you need to convert to a fully-adjustable Watt's-link setup. And even with my Dana 60, I see enough space to make it happen.

hellz_wings

iTrader: (2)

It doesn't lower the center of gravity at all, it lowers the rear roll center. The center of gravity stays the same but the roll center moves lower causing all sorts of cool things to happen lol. (more rear grip, more rear brake bias etc.)

Actually, if you count the PHB's weight, that sits now 2" lower (for me, atleast) then yes the rear CG is probably a fraction of an inch lower, although negligible.. But this is the only reason I can think of that would make this lower the CG in the rear..?

Pablo

iTrader: (1)

Hate to be the bad guy, but this is incorrect. It is really changing the RC height not the center of gravity. A watts is not going to get your RC as low as panhard bar.

Google it.

Atilla the Fun

In the drivetrain related threads, especially SBC related, I respond quickly. Here, I not only took time to think it through, but I built a couple of scale models. After that, I have this to say: Were you to believe your stock roll center was wherever the panhard intersected the centerline of the car ( which doesn't hold ) then this whole thread makes perfect sense, except for me. But once again playing Galileo, questioning the common assumptions, I found we really don't get such a fixed roll center. But it seems a lower roll center is the subject under discussion, and how to get it. This assumes you have a good reason why you want it lower, beyond someone telling you lower is better. I'm not really seeing good reason to move it at all, unless you're doing an awful lot of on-track testing for very specific racing. On the public roads, there's no advantage you can use without going to Jail when a cop eventually sees you. So if you think you see a value under legal driving conditions, that would interest me and possibly many others, I expect.

hellz_wings

iTrader: (2)

Well there is value. It has helped keep my rear planted in the turns. It changed the feeling of a turn big time, there's barely any oversteer anymore even when I floor it (I did floor it today for the heck of it and got MILD oversteer.. This is a good thing).

As for cops arresting you, well turning a corner quickly won't put you in jail where I live.. But oversteering/drifting around a corner, creating a large cloud of tire smoke will attract a cop's attention and perhaps get me a ticket for "reckless driving". Lower the rear roll center actually reduces the chances of this happening because it increases rear body roll which gives our cars a more neutral handling feel as a pose to massive oversteer.

Pablo

iTrader: (1)

No one said the roll center was fixed. It does migrate slightly with suspension travel. You are changing the height from which all these small migrations take place though, and thus, changing the effective roll center height. If you lower it 4 inches that is very significant.
You may not see a good reason to move it because as you have alluded to, you only drive safely and legally on public roads. So for you, I actually don't see any reason to modify your car in any way. Different strokes for different folks.

Others, such as myself, are chasing tenths of a second on the track, or we aren't as worried about yet another law we might be breaking (there are enough laws to criminalize almost every human activity in some way now), so this kind of adjustment is important. On the track I can feel the difference from moving the bar 1 inch.
When you change the roll axis inclination you change how weight is transferred fore and aft with body roll. Inclination to the front causes weight to transfer away from the inside rear tire to the outside front tire which increases the load on the already heavier end of the car.
Now you might think, why don't we have a flat line for a roll axis? Well in order to do that you would need to increase the spring rate in the back significantly relative to the front to maintain the same handling balance. Unfortunately the car is not balanced the same front to back weight wise neither are the sprung to unsprung mass ratios. This would lead to a very harsh rear end also harming braking and performance over rough pavement.

By the way, I also built a scale model of this. Full scale.

83RDRACR

Here are some pics of homemade phb mounts on a ZR2 8.6 axle. Adjustment is from stock to 7" below stock. The brackets and and aluminum phb and brace are stock car items from Allstar Performance and the rod ends are 3/4" QA1 items. I will probably not use the lowest holes but will try them out when the car is finished and dial in the car. The side loads on the axle and body brackets can easily be in the 5,000 to 6,000 lb range under hard cornering so bracing for lateral loads is important.

The full 3 link install is on Fab forum under "home brew road racer".

SCCAjunkie

Pablo,

I have a friend who is really considering the Watts Link from Strano. Most of this is because he is concerned about the slight lateral movement of the axle as the panhard travels through its arc. With his current setup, he has issues with tire rub. He says his panhard is level at ride height and roughly level with the axle centerline. I was talking to him about trying the Panhard relocation, and he's really thinking things over, but still likes the Watts Link a lot.

From my understanding, RC should be at the center pivot of the link, correct?

Also, Strano claims to be able to adjust RC 3.5" lower than stock. Does that make sense from what you can see on the page I linked above? How does that compare with the RC of a lowered Panhard?

Also, right now, I'm not even sure exactly where his front RC is at. Admittedly, I'm only learning about this stuff at this point, but I tend to pick things up quickly when I have good info. I only got into this discussion with him because he asked my opinion on the Watts Link idea.

Once again, the amount of quality info on here is amazing. While I always thought I knew quite a bit about suspension setups, I've found that I work very well within stock adjustability and doing test-and-tune type tasks, but when it comes to re-engineering things, I've still got quite a bit to learn. It's always amazing how as you learn more, you find out how much more you never knew...

Pablo

iTrader: (1)

That is a very cool build you have there. I also did aluminum PHB (and LCAs) using parts from coleman racing and I also used the QA1 Rod ends.
I will have to go through the thread and see all you have done

Pablo

iTrader: (1)

Well if that's what Strano is claiming who am I to say otherwise. In the picture it is really hard to tell how far the pivot can go down.

There is a bit of misinformation on his page though, his watts is a reverse watts and it does in fact make the axle move in an arc. The radius of that arc is the distance from the pivot to the centerline of the axle.

So the lower you move the pivot on his setup, the more the axle will move laterally. Not a good thing IMO

Obviously this guy is multiple time nat. champ in esp and stock (possibly others?) so it can work.
I personally don't see the advantage to it but what do I know, I have a much shorter resume. What I can tell you is that thing is freaking expensive. I spent only a little bit more than that for a whole dana 44 rear end.

I think what it comes down to is that there are many ways to skin a cat. Like I always repeat "Excellence is more about execution than type". As an example, my three series BMW has IRS yet my Camaro would utterly annihilate it in any sort of handling competition. Doesn't mean IRS is bad at all, just that there are many more things to consider.


I think you'd be money ahead to focus on eliminating brake hop and then maybe a way to put toe and camber into the rear axle.

SlickTrackGod

83RdRacer- Nice job on the 3 link and coilovers.

Now a general note for all-

What is important to remeber in roll centers is the "Roll Axis" and the CG (cneter of gravity) of the car pertaining to height off the ground. They need to be close to eachother witht he roll axis in the level you desire for balance (based on spring rates and driving style feel- lots of correct combo's based on taste)

The lower the roll axis is from the cg? the more positive roll of the chassis occurs- THUS- the need for large swaybars to resist body roll. The byproduct of this is loss of mechanical grip due to the larger swaybars locking up any independant wheel movement side to side. Food for thought.

conclusion? Who needs 3.5" rear RC adjustment unless you have stripped the car of upper roll weight bigtime and lowered the overall cg height. VERY FEW.

SCCAjunkie

Dean,

I don't think it's the range of adjustment that's the big draw. I was simply questioning Pablo's statement that you couldn't get the RC as low as with a lowered PHB.

Pablo,

I'm not sure I see how this Watts link would result in lateral displacement if you set the pivot so that the axle height would not pass the upper pivot at full bump. Am I thinking incorrectly? Keep in mind, I'm making the arguement to stay with the Panhard, so I'm not sold on the Watt's Link either, especially at that price.

hellz_wings

iTrader: (2)

Hey Dean,

I thought the affects of the roll center were solely related to it's height in relation to the height of the CG? I did not know that its height related the ground had an effect as well.

I agree with you on "lots of correct combos". I for one, with 24mm rear sway bar and slightly stiffer rear MOOG 5665 springs (they were cut 3/4 of a coil), find that using UE's PHB relo bracket in the lowest (and only) hole resulted in much better street friendly handling (much more rear grip as opposed to oversteering). It appear grip is nearly endless and you can hear/feel the car starting to lose grip from the tires EVENLY during mid-turn, and coming out of the turn it has excellent grip. Going into the turn there is very slightly oversteer but I can deal with this since at that lower speed it is easily controllable. I've never lost grip mid turn yet but I've yet to test on track, just tested on brand new twisty street roads with very large roundabouts (sort of like a giant skidpad lol)

FWIW, I have done massive weight reduction/relocation on the car and have lowered CG properly (extended ball joints, not lowering springs). The car sits at about 3350lbs with a full tank of gas so for a V8 this is decent IMO. More weight reduction in the right places to come (snatched up an excellent condition 1Le aluminum front bumper support that will go on after car is painted over the winter) and will be installing 383 with aluminum heads (bumper is front polar weight and the alum. heads is over front wheels but is higher than the CG, this should lower the front CG slightly).. this should also help with rear traction and FR weight balance and put less weight over the outside front tire during cornering which means the FR outside tire should not lose grip as quick as before the weight reduction.

SlickTrackGod

You are correct- it is the height of the Roll Axis to the height of the CG- I said that but was unclear in my statement- let me clearify....I was speaking in terms of the "cg" when I said height from the ground, Rather than, the CG of the car side to side or front to rear. All of them matter- but for discriptive purposes I was simply refring to the imaginary CG point of the car in vertical level as opposed to the roll axis height in vertical level when I stated the "ground" reference. I should have just said "vertical CG".

Sorry for the confusion.

hellz_wings

iTrader: (2)

Question: Instead of getting stiffer rear springs to control body roll, what about stiffening the rebound dampening on the KONI rear shocks? Wouldn't that reduce rear body roll slightly enough without increasing ride harshness of stiffer rear springs?

SlickTrackGod

Rebound is in fact what controls body roll in dampering- so yes. Too much rebound will cause the car to skip the tires over bumps. Yolu will feel the car start to ride "hard" in the tailbone when the rebound get upward. you will start loosing a tad bit of mechanical grip when this happens -there are plus and minus+ plus is reduced roll, minus is loss of mechanical grip and loss of brake traction if rebound is set too high for the chassis setup.

Larger rate springs will obviously make a rebound setting return faster, and visa versa.

Keweping the roll axis in check (more balanced reducing vehicle roll canter) will keep the inside rear tire more weighted and not lift the chassis here under hard braking corner entrance- thus the lesser need of larger front swaybar, the lesser need of higher rebound on the rear dampers, the lesser that you'll need to reduce the rear swaybar size to reduce wheel lifting...and thus you will have more rear brakes to apply.

All you can do is try the adjustment settings one click up at a time and test drive it in the same enviroment to get a feel of the car. The car will become more predictable, but often too much "more predictable" is just a controlled drift with loss of rear traction.

hellz_wings

iTrader: (2)

From what I gather, setting the clicks upward one click at a time will make the rear more predictable, but to a point in which case it will then lose mechanical grip, in which case there is too much rebound dampening? Interesting, I always thought since the car is leaning on one side, that the increased spring rate will make the car compress less on the outside, but what I forgot was that by increasing rebound dampening it seems that you are transferring less weight over the outside tires and keeping it over the inside tires.. Does that sound right?

SlickTrackGod

Actually no, that is not correct. Let me give you an analogy that will explain dampering better.

Think of a car sitting still on a line and you pushing it 5 feet forward.

Now, think of a car rolling at you and you need to slow and stop its momentum, and then get it moving in the opposite direction to that 5 foot mark from that line you first made contact with it.


Now lets try and apply this to the rebound priciple-

The car will roll into the corner and compress the springs the same static compression at steady state regardless of dampering-THUS- the tires will weight the same when settled in steady state (mid corner) regardless of the shock settings.
OK, then what changes? The time interval it takes for that motion to settle into static compression from stagnant position into the corner....and then the recoil back to stagnat position coming off the corner. The rebound simply slows the MOMENTUM of the movement so it is not cycling as hard in frequency- just as the motion of the car rolling towards you comes past the line in a negative measurement prior to pushing it positive.

The by product? is too much rebound will slow the motion too much where it starts to lift the tire up off the ground as the body rolls- this is called rebound skipping and is what causes a momentary loss of mechanical grip until the chassis sets into the static compression at mid corner (assuming the ground is prefectly flat with no bumps or dips).

New2Chevy

iTrader: (11)

Does that "pipe" come with the kit, or are you just adding it in?

New2Chevy

iTrader: (11)

Wow lots of info here.

So, what's the benefit of making the PHB level?

Better rear stability?

hellz_wings

iTrader: (2)

Hey,

The pipe comes with UE's kit, yes. It's the needed re-inforcement bracket to support the lowered PHB axle mount. This piece would probably break off if you didn't have that if you road race the car.

Leveling the PHB reduces the "rear jacking effect" that happens when you turn in one direction vs the other on a car with a PHB. This is inherent in the design and can be reduced by making the PHB as level as possible (it's better to set the car's final height, then use the brackets to level the bar. The axle side should be SLIGHTLY lower than the body side, like half of an inch to one inch MAX. Because as the body rolls in a turn, the body side mount lowers itself towards being level with the axle mount. As you can imagine, stiffer springs would also reduce this effect). Lowering and leveling are two different things. JEGS sells just the axle side if you want to only lower that side so that you can level the bar when you lower the car alot.

If you want to lower BOTH sides of the PHB mount, then what you are doing is lowering the rear roll center (making the rear roll more in the turns, this also has other effects like reduces front nose dive during braking.) If your car oversteers alot, then you can either:

1) lower spring rate springs in the rear
2) install a smaller sized rear sway bar
3) lower the rear roll center by lowering the PHB

I opted to lower the PHB and it works well although my only gripe is that when transitioning from a quick right to a quick left while on full throttle, the rear doesn't react as fast as the front so I lost some transitional speed/feel in the rear which sucks and I might either increase the spring stiffness or install a bigger rear sway bar. Haven't decided yet..

New2Chevy

iTrader: (11)

Hey cool. Thanks for your reply!

I'm in the middle of swapping in new SLP Bilsteins and Strano springs, in my 95 Bird. I also did the LCA relocation brackets and adjustable PHB.

I'm also thinking of going with Strano's hollow sway bar kit. Sam Strano uses this sway bar setup and wins a lot of races with it. Of course, he also uses Koni shocks.

I'll see how she handles with these mods, before I level the PHB. At least, she won't feel like a boat on the lake anymore, since I am getting rid of the 18 year old DeCarbon shocks and stock springs.

I am thinking about going with the UE de-coupled tunnel mounted torque arm. I've read a lot about the other torque arms, and they seem to have clunking issues and other issues.

I appreciate your thread here!