vsixtoy

For lesson #1 on drag launch geometry- please resort to this thread from others- Good examples here. https://www.thirdgen.org/techbb2/sho...hreadid=235762

Lets take this another direction (if not well rested and clear headed, then might I suggest taking a nap first )

Below is a "hillbilly sketch" of how LCA angle can adversely affect the way your car corners. This graph will show how the back tires can utilize rear wheel steer and small slip angles to help hold a corner, or the opposite- make the *** end steer out from under you.
*PLEASE NOTE THAT THESE SCKETCH ANGLES ARE EXAGGERATED FOR EASE OF UNDERSTANDING.*

Ex1 a&b- show a car that is lowered with LCA's set parallel to the ground at stagnant height. (Longest geometry point) Then to the right it shows how the outside(of the corner) LCA will shorten and thus turn the axle the same as the front tires turn when the car leans.

EX2 a&b- show a car with LCA's set with the rear mount points lower (for frontline traction, and "maximum" wheelhop elimination)
Then to the right it shows how the outside(of the corner) LCA will move towards parallel and lengthen in geometry- thus turning the rear axle outward away from the direction of travel.

These examples show why it is important to set LCA angle as paralell to the ground as possible WITHOUT the occurance of "severe" wheelhop. Sometimes a slight "off the line" wheelhop is an O.K. compromise for greater handling carateristics.

This is another "tool" for tuning an balanced suspension setup

Mavrick

so you are saying for an autox or roadrace setup, you do not want to use relocation brackets? That having the increased angle will actually hurt my cornering abilities.
I'm actually building my car for more of a autox use, as opposed to drag, and am relatively inexperienced when it comes to setting the car up. But post like these and your SFC ones help a lot. Thanks for al the time you put into these exlpanations.

vsixtoy

Mavrick, I have LCA relocators on my car. It is lowered and used for handling purposes like autox and roadrace type setup.

What I am saying with this post is that one should not always assume the lowest mount point of the relocation bracket is the best setting, its generally not unless you have extreme traction (Slicks, or just very good tires) and/or the car is extremely lowered, and/or very low rate springs with lots of suspension travel.

If the car pushes through the corner- try lowering the rear setting

If the car is loose(*** end hangs out)- try raising the rear mount point.

Picture of my rear LCA setting- note its in the middle position. And my car is lowered more than most- but less power also. (wheel is off the ground in that picture, so the suspension is unloaded)

Mavrick

Ok, lets see if i understand this. So with a level LCA, when you go through the corner the body rolls outward causing that side of the car to push down. This pushes the LCA connection at the body down, which in turn shortens the horitontal component of the LCA length. This, in turn, pulls that side of the axle in which will help with and oversteer situations. Is that correct?
Now if that is the case, wouldnt the inside LCA be doing basically the same thing, only the LCA will be pulled up as opposed to pushed down? As the body rolls outward, it pulls the inside up, which in turn pulls the LCA mounting point on the body up. So in this case, the LCA's horizontal length shortens and the inside axle gets pulled in as well. So in the end, both sides of the rear end are being pulled inward, and there would be no net effect?
Now, I am probably completely wrong in my assumption, as I know you know what you are talking about. So what in my thinking is wrong?

vsixtoy

You are actually very correct on right on track. The example you gave above would have the rear set at a "neutral rollsteer" setting. Now for sake of arguement, that is hard to set exact based on ride height, adjustment provisions, rear roll center, springrates, and swaybar setting/size.

You will generally be above or below the neutral steer point, but not right on it. Each setting will give a different feel to the rear of the car- but everycar is different based on the variants I listed above. So its up to each of you to test your own setting by moving the positions to optimum balance levels.

Some cars may only produce roll oversteer, and without being lowered +adding relocators, the roll oversteer can only be increased or decreased- but never be able to adjust into roll understeer settings.

It depends on ride height, angle of LCA, and amout of travel(swing) the lca's do.

(This may get confusing for some, its starting to get a little advanced)With a lower rear roll center, the inner LCA will unload less on the roll axis than the same setup with a higher rear roll center. Rear Roll center is determined by panhard rod relocators- this also affects weight transfer front to rear. Jerrywho has a great fabb job on a custom homemade setup- https://www.thirdgen.org/techbb2/sho...hreadid=213390

Adjustments like this often require change in swaybar size and spring rates because of leverage increase/decrease on the rear suspension.

Mavrick

Well at least my intuition is correct, even if I dont know exactly how to adjust everything. I just finished up my suspension (see here for list of what i've done). I havent had a chance to really try it all out yet as i've been busy with finals and getting ready to move. Hopefully over the summer I will get a chance to do some auotx races and learn what and how to adjust my suspension.
That relocation bracket for the panhard bar is interesting. By lowering the bar, you are increasing the angle of the bar. Now depending on which way you turn, the bar will rotate accordingly. Like if you make a left hand turn, the angle will decrease, while if you make a right hand turn the angle will increase. how exactly does this affect whats going on in the rear. It seems you would be having 2 different situations depending on how you are turning. Right hand turn, the panhard bar/body mounting point rises pulling the rear end in. left hand turn, the mounting point drops, pushing the rear end out. Am i understanding this correctly? if so, what exactly does all this mean

vsixtoy

If the bar is angled enough then yes you are correct and you will have more weight transfer to the right turn, and less rear to front weight transfer to the left turn because your instant rear roll center will be moving up and down more than usual (always moves slightly at the very least).

At stock ride height, the bar is mostly paralell. Lowered the bar will invert. Invertion is not bad like the opposite (angles upward) because forces will squat one side slightly, and basically about neutral the other- but still not best- closest to paralell is best entering the corner. This can still always change based on brake dive or moderate acceleration. There is no perfect world, just a happy medium(why setups vary based on track style).

The advantage we have with these cars is the length of the panhard rods. They are very long and suffer very little if at all from geometry change. Shock dampen forces can and do overpower panhard geometry travel (with good roadrace shocks)- so small incline/decline angles are not nearly as crucial as a shorter panhard rod.

Most performance racing suspensions on 3rd gens are lowered, thus inverting the panhard rod angle (like mine) currently I stand at (from ground height) 12" to center bolt on axle side, and 10" to center bolt on chassis mount side. My car could really benefit from an adjustable axle side bracket like Jerry fabbed. My rear swaybar is just slightly too stiff and lowering the axle side mount 2" would 1)lower my rear roll center 1", and 2 & 3) produce more leverage on my rear swaybar(making it softer), thus creating in essence more squat in the rear(less rear to front weight transfer, creats slightly more push), and more roll on the rear axle (keeping the inside more planted, and creating even slightly more roll understeer)

All in all, this simple little adjustment compounds many things- but in my senerio would greatly benefit me because I have a very radiacl turn-in response that can be a bit touchy at very high speed(100+) Car won't get loose, but it will wander just a bit on unsettled surfaces- enough to jiggle the wheel a 1/4"-1/2" otherwise it can always be driven with 2 fingers (Its either that , or put a bigger rear spoiler onto it to control the air and plant the rear more at speed ). The *** end also wants to creap out on the tail end of sweepers just coming onto full throttle(I'm slightly lifted pressure on the inside rear wheel on exit). I'll get to copying Jerrys design someday soon- just have many other priorities in life like installing windows on my house right now.

Mavrick

I did not know the panhard bar sits that way. I always thoguht it was highest at body side, and angled down towards the axle. I have the tokico springs, and supposedly they lower the car about 1"-1.5", i know that not much, but it stil lowered.
So like with the LCA, you want the panhard bar to be parallel in a nuetral setting? and on your car, the bar is actually angling up towards the axle? Interesting. I need to get out and measure mine and see what it is like.
I'm curious, have you done any of your own special mods to your suspension that you wont find elsewhere? also, where exactly are you racing that you get to race 100+ mph turns? Obviously that isnt autox. I would love to go for a ride in your car through one of those turns

vsixtoy

"So like with the LCA, you want the panhard bar to be parallel in a nuetral setting?and on your car, the bar is actually angling up towards the axle?"

Yes, and Yes.
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"I'm curious, have you done any of your own special mods to your suspension that you wont find elsewhere?"

You'll see a couple of aluminium shft rodend chassis braces-One on 1, the other on page 2:
http://www.cardomain.com/memberpage/518752/1


------------------------
I had it on Calif Speedway clocked at 123.3mph through bank turn 1 with my handheld GPS (I wasn't suppose to be over 85mph though). Given the chance, AND THE POWER(which I don't have) the car could have handled another 40mph faster through that bank on the street tires(160mph)- but without my 270# passenger aiding with banked spring compression. Here's a few shots I've posted before: http://www.cardomain.com/memberpage/518752/4

I had been through that corner two years back in our Vette at 150 but it was pushing up towards the wall. The camaro is lighter and handles better.

vsixtoy

A teaser for everyone-

Pictures of a Custom 6-piston 13" 2-pc rotor brake setup with aluminium hubs that will fit under an 16" Iroc rim coming very soon! Parts are ordered and coming tomorrow- then the fab work begins.

Mavrick

good g*d...6 pistons? I can only imagine how much something like that cost. I'm looking forward to just getting some 2 pistons from baer to replace my stock brakes. Someday, I will have a setup like you though, and I cant wait

I wanna thank you again for all the time you are taking here. Its so nice to come to this board and actually read informative topics like this, as opposed to the usual topics rehashed over and over.

JPrevost

So who's going to be the first to run under their car and measure up all the suspension points so I can model it in A.D.A.M.S. Car? Any takers?
Here's a little something I through together last night in Solidworks. I can import the origin points into Adams but it's a lot easier to measure and visualize with solidworks than it is in Adams. From this I'd like to figure out exactly what is truely going on with vehicle roll and pitch. How the whole car's suspension works . We have a few guys on our formula team that need to get good with Adams so I figure this is a good start. On a side note, I modeled my engine in Virtual 4-stroke so that I could get used to the software.... always helpful don't you think?
I'd really like to figure out what can and should be tweaked on our cars for the drag strip, autocross, road course, and road noise (daily driver). Adams will definatly help figure out some flaws or area's for improvement.... especially on lowered cars! All I know for fact is that after I lowered my car I was getting crazy wheel hop. 2.2 was my best 60' and on the street I had only 2 options, one was to spin them off, the other was to wheel hop. Needless to say the LCA relocation brackets solved my issues. One thing else that I noticed is that beefy (Hotchkis square) LCAs will lower the frequency of wheel hop into something more predictable and manigable. Light weight LCAs and lots of power plus wheel hop = no fun.
So... who's going to measure all of the suspension points .
Oh, and vsixtoy, what calipers and rotors/hats are you using? I've got Wilwood 4 piston Billet superlites that I'm going to be installing with either corvette or LS1 rotors. The c5 vette rotors are $23 a pop at Napa so I'm hoping they'll fit. The other option is like you, 2-piece... I just want to save as MUCH money as possible when upgrading. Which reminds me, I need to hit up the local j-yard for spindles and misc other parts.

MrDude_1

your model is backwards.. the panhard rod connects on the drivers side and mounts to the chassis on the passenger side.

i do want to point out, that while what he posted is 100% true and will make a large diff in autoX and other tight turns, if the turning you do does not induce alot of body roll (like fast sweeping ones on the hwy for example) then the effect is minimal.

not puting down what vsixtoy said.. hes 100% correct... but just putting in into perspective.
inotherwords, if you were to race on a open roadcourse, you might want them lower (like my drag race thread linked above) so that you hook harder coming out of the corner under power.
however if you were to play around tight turns, like autoX, his setup would be better.

i guess what im saying is, they're adjustments. we arnt telling you how to setup your car, just what they do. its up to you to decide how you use the car and want it setup.

once you have a grasp of what they do, i reccomend playing with all the adjustments just so you can feel how they react.

Dewey316

my car rolls in highspeed turns too.

well forward traction is great, i reality when your exit speed is 60+mph you have to have ALOT of power to really have to worry about 'forward traction' you are ALWAYS going to be best off with a well balanced suspension, too much anti-squat can hurt as much as too much.

RB83L69

Putting it into perspective is the most important thing.

The overall magnitude of the effect of this is so tiny as to be unnoticeable on the huge najority of cars. The improvement in the car's ability to plant the rear under power, results in such a huge improvement in traction, that for most cars (street cars especially) the other thing is a virtually unnoticeable fine-tuning effect.

Seems like we've had this discussion before..... when this individual was using some other user name, and subsequently got himself banned, and had to re-register.

According to the calculator, assuming that the LCA is 19" long (I don't know the exact length, but it's somewhere close to there; if anybody has the measurement I'd be happy to use the exact number and modify the calculations accordingly) then a suspension deflection of 1.5" (pretty severe for most of use on the street) away from the point where the LCA is exactly horizontal results in the LCA moving to an angle of just over 4.5°. This results in a change in the cars wheelbase of approximately .118" (pretty tiny). To put it in perspective, stock rubber bushings deflect more than that just from the car's weight; and your frame deflects several times that amount when you go over a driveway or something. I'd suspect that even with SFCs, your frame will bend more than that under sufficiently sharp cornering conditions to produce that amount of suspension delfection.

Also keep in mind that as you go into a corner, then after the shocks have allowed the suspension deflection to reach its equilibrium, the 2 sides of the car will be delfected equally in opposite directions. At that point the 2 ends of the rear end will both be moved equally toward the front of the car; and there will be no roll steering effect at all from any of this, except for the Panhard bar moving the rear to one side or the other. The car's wheel base simply will get a little shorter.

Therefore one can conclude that if your LCAs have any sort of bushings other than new tight rod ends, this effect is negligible for real-world handling. It is strictly a fine-tuning adjustment for a properly prepped race car, after most other coarser adjustments have already been optimized. It is certainly not a reason to avoid LCA RLBs; or, for that matter, a reason to put them on.

MrDude_1

yup.

and i should have "ALOT "of power.

but mines a fun car, not a race car. its not setup perfect for drag racing, and its not setup perfect for autoX.. its just a nice balance that works well for me.

Dewey316

there is nothing wrong with balance, but there are alot of factors. relocatin the suspension points can go to far, even in drag racing if you get to extreme, you get a ton of inital bite, then unload 10ft into your run. same as in cornering.

RB-- yes we have all gone into the roll steer thing many times, i still remeber the the last time this was discussed. you have to put it in persective. those of us who do worry about roll steer, can tell when we drive on the streets, if we are a couple of PSI off in 1 tire. roll steer steer does happen, you down play it, dean may make it more of a deal than it is, but please don't try to say that it is not noticable, it is if you know what you are feeling. but with so many diffrent feelings while driving, it is hard to say, that is too much rear spring rate, that is too much rear sway bar, that is not enough dampening, that is roll steer, ect. but i can tell you from experiance that i know where my car likes the LCA's set up, and where it doesn't. if i lower my LCA's to the lowest setting I CAN FEEL THE ROLL STEER.

MrDude_1

hehe, if im paying attention, i can feel tire pressure, the wheels bite, ect... but the most noticable one on a 3rdgen is the stupid panhard bar arc.

Dewey316

the panhard thing isn't as huge of a deal to me, with such a long PHB, for a couple of inches of susp. travel, there is a VERY small amount of of lateral movement (IIRC we figured 3/16" for 3" of travel) (don't quote those figures, it has been a while and i am too lazy to do any math now) since the LCAs are shorter, for the same amount of suspension travel, the move the mounting point considerably more.

vsixtoy

RB, take note in the picture I posted above that my relocators are positioned more forward than anyone I have seen in here. Why did I go to this style with forward mounting points?- simply so I can run my LCA lengths as short as possible (just enough not to stuff my imput yoke into the trans and ground out). This makes my geometry swing change jsut a little more than stock lengths (every 1/100 counts in racing). You stated that the movement of the axle would be aprox. 118" forward. Going with that figure. This would reciprocate the opposite direct outward if I set for roll oversteer. That calculates to an entire 1/4" of rear steer in the opposite direction- Desn't seem like much to many- but thats alot of movement inward/outward as for how the car reacts (turn your front tires that same degree and see the car move to that side.

This is as stated above just one small tool in suspension setups- alot of smalls clicking in the right order add up. People win or loose races by thousandths.

Come ride in my car sometime, you'll sh*t- everyone does.

BretD 88GTA

Talk to Jason Swindle at Unbalanced Engineering.

"Panhard Rod Relocation Brackets
Laser cut steel brackets that relocate the panhard rod to lower the rear roll center 4 inches and also level it for lowered cars. These brackets result in additional rear grip in all phases of cornering. They require a panhard rod with 3/4" rod ends and a welded installation. Cost $150"

http://www.unbalancedengineering.com/Camaro/

Dewey316

i've talked to jason many times about this. (BTW, jason is a great guy, and LOVES to talk suspension)

there is alot of benifits there, in a perfect world, you pick your ride height, find the front roll hight, then match the rear to that. your ride height has a HUGE effect on the front roll height (much more than it does in the back). 4" may be too much for some cars, in other that may not be enough. i am working on an infinatly ajdusatble PHB mounts, that will allow for fine tuning the rear roll height.

BretD 88GTA

Very nice. I'd definietly be interested in a set.

Mavrick

well this went way over my head a while ago, but it is still very interesting to read. Plus it is nice to see that there is so much I can still do to make my car handle even better. Keep all the good information coming

vsixtoy

Jason has sent me pics awhile back on his setup- Its nice, but not enough adjustment range for my needs on the axle side. His are bracketry on both sides and is more suitable to lower the roll center on a stock height vehicle via both sides. I personally don't want to lower the chassis side mount any lower than it already is (Don't feel its safe personally because of increased leverage against it). One side would put me at aprox the 2"drop for level- Byt Jerry's design give about 4" drop for further adjustment needs (there if needed). My chassis side is prefectly adequate.

I have seen Jerry's setup in person down at Don's shop- It was very strong- he did a great job.

BretD 88GTA

Jerry does do nice work. Did you ever see his tubular A-arms he made? Supposedly he had a buddy that was going to make a version with spring perches, but it never happened to my knowledge.

I have some ideas for little accesory items on my car, but Jerry isn't too into doing custom work. He prefers just to tinker on his own car.

Mavrick

nother thing i was wondering about. In Nascar they will often adjust the trackbar, which is the same as the panhard. Now I know what they are doing is mainly only benefitial on ovals, but how exactly is their adjustment helping? If i understand correctly, they are lowering or raising the chassis mount and this would increase or decrease the angle the bar sits at. Now you said your chassis side is 2" lower than the axle side, but once you get it level with the relocation brackets, couldnt this be somewhat helpful? Perhaps on a track where you are making most of your turns in a specific direction, or at Fontana when you get up on the banked turn?

Dewey316

which side is heighter changes the track change under bump conditions, what they are really changing is the roll height. the roll height is the point at which the PHB crosses the center-line of the car. you can manipulate the roll charictoristics of the car, by changing the roll height, what you are REALLY doing is either giving the car more or less leverage to roll over in the corners (roll height vs. CG) when they adjust the track bar they are doing is trying to give the car neutral steer.

Eggplant Jeff

Let me see if I understand.

1. Install LCA lowering brackets. Now the LCAs are higher at the body.

2. Take a hard corner, introducing massive body lean.

3. The outside rear corner moves down.

4. The inside rear corner moves up.

5. The outside LCA becomes straighter, meaning longer.

6. The inside LCA becomes even more diagonal, meaning shorter.

7. The thrust angle of the axle is now pointing in the direction of the body lean (I.E. turn left, lean right, axle now points right).

Conclusion: Lowered LCAs produce OVERsteer.

Now, if I currently have an understeer problem, wouldn't that mean LCAs would be a good all-around mod for me?

Or does it mean I need more power, so I can break the tires looser on a turn?

Chickenman35

No you do not want to play with LCA angles to produce oversteer. You adjust your bars, springs and shock settings to balance the car.

Oversteer induced by LCA angles is called Roll Oversteer and it is very unpredicatble and sudden. In a roll condition ( cornering ) you can go into a " Snap" oversteer condition. Just hitting small bump can immediately spin the car. You do NOT want the rear end steering on you if at all possible. On cars with LCA's this is not possible so the LCA angles should be setup to give a small amount of Roll understeer. Roll Understeer is a stable condition. Roll " oversteer " in most cars is an Evil handling condition and should be avoided at ALL costs.

It can be very dangerous....take it from someone who almost went flying off a 250ft cliff at a Hillclimb, because he got his LCA angles wrong ( Trying to get more anti-squat ) and induced Roll Oversteer. Just as dangerous on the street BTW.

Edit: Spelling