road course suspension help

[malibu43]

hi guys,specially to NORM,i will like to have some help to get things done right.
i race my bu as a road course,so any help try to focus in this kind of race.
1.the lower rear arms has to be parallel to the ground as possible?
2.what should be happen if i took apart the upper control arms,and instead i change to a 3 link with a panhard bar?. if this set up its ok, whats the position of tyhe pb has to be?,any pocs will help me.
3.if the set up above its ok, do i need the stock stabilizer bar?
4.for road course, do i need to change the poly bushings to the stock ones, i understand they try to fight one to the other?.
i know its to many question, but i think you guys are my best and only source.
thanks and regards from the farest place on earth.
jorge.

 

[UMI Sales]

Hello
My suggestion to you would be just stay with the factory 4 link set up and go with adjustable suspension components and doing so will allow you to make any adjustments that are needed. And instead of worrying about a pan hard bar I would just go with a bigger aftermarket rear sway bar to eliminate your body roll. Below is a link to show you what UMI Performance has to offer!

http://www.umiperformance.com/catalog/index.php?main_page=index&cPath=8&zenid=jchaejjbd0gv975a6i1ktmbq05

If you have any other questions feel free to ask and I will be more than glad to help!
Thanks Again
Brad

 

[Norm Peterson]

Briefly, because I'm on some hotel computer.

hi guys,specially to NORM,i will like to have some help to get things done right.
i race my bu as a road course,so any help try to focus in this kind of race.
1.the lower rear arms has to be parallel to the ground as possible?

This depends on what else you do or don't do. Parallel to the ground works better with 3-link and torque arm suspensions where the single upper or TA is not part of the axle steer geometry. If you retain the triangulated/converging OE 4-link, then it's my opinion that you want the rear lowers to run slightly uphill from axle to chassis. This will remove some of the reluctance of these cars to execute slalom maneuvers.

Usually LCA relo brackets are seen as being strictly drag-strip mods, but this is one situation where cornering may also benefit.

2.what should be happen if i took apart the upper control arms,and instead i change to a 3 link with a panhard bar?. if this set up its ok, whats the position of tyhe pb has to be?,any pocs will help me.

I'd start out by setting it at axle height and level with the car as normally driven (with driver seated and half the normal fuel load). Being able to adjust it from there is nice but perhaps not necessary until you've got some seat time with the different suspension.

If you go this way after playing with LCA inclination with the OE 4-link, plan on dialing out a little of the LCA inclination (back to level, or at least closer to level). This will depend on the PHB height (and personal driving preference).

3.if the set up above its ok, do i need the stock stabilizer bar?

Once you lower the rear geometric roll center, you'll need to add some rear roll stiffness, either by replacing the springs with stiffer ones or by adding a stiffer rear sta-bar. A stiffer sta-bar might be either a larger-diameter bar that still attaches to the LCAs or a bar that uses endlinks to either the chassis or axle.

4.for road course, do i need to change the poly bushings to the stock ones, i understand they try to fight one to the other?.

If you have poly bushings, you can tune around them to some extent, typically with softer springs or a thinner sta-bar than you would otherwise choose. But it's still better to remove the roll stiffness that poly bushings add and use real springs and bars to do that job. There are ways of softening poly bushings that can be used as a stopgap measure, at some cost in bushing durability and other inspection and maintenance.


The real nitty-gritty comes down to testing for yourself, and what you end up with should probably differ if you're at relatively high speed on a real road course vs most autocross (nearly always below 65 mph even in things like Z06 Corvettes). Basically, handling that's only a little "loose" in a 2nd gear parking lot autocross could be way too loose at 110 mph with Armco.


Norm

 

[malibu43]

thanks NORM for the reply,i got more questions for you,what its the roll center? please be very basic in the lenguage,i understand that the more low the ride height ,the higher the roll center, its is true ? and can you tell me how it works.and how can i solve this issue.
thanks again regards
jorge

 

[Norm Peterson]

Fairly precisely, the "roll center" is the height above the ground at which a lateral force does not cause any roll. It is not necessarily some point that the body actually rotates about (and generally is NOT such a point, though it can be close).

Part of what it can do is limit the amount of roll that happens without increasing spring rates and sta-bar stiffnesses to some uncomfortable level. The higher you put the RC, the less roll happens. But it's a trade-off, because as the roll centers go up it becomes more difficult to tune the handling balance (larger increases or decreases in spring rates and/or bar sizes become necessary in order to achieve the same effect).

With the OE G-body triangulated 4-link rear suspension, it is true that the RC moves up as the car is lowered. But at least it doesn't move all that fast (perhaps moving up 10 mm for every 30 mm that you drop the chassis).

Actually, if slalom or other rapid right-left-right maneuvers are common and you retain the C4L (aka triangulated/converging 4-link - I'm getting a little tired of typing that whole thing out :lol: ), I'd be more concerned with roll steer. I think that steady-state, you can tune around a high RC better than you can tune roll steer and front vs rear roll center heights for the transients (think corner entry and exit). That's why I mentioned SLIGHTLY lowering the axle side LCA pivot point holes; this will reduce the excessive amount of OE roll steer without driving the "roll center" too far upward.


Something that I didn't get around to before is that adding a PHB to a C4L will improve lateral location of the axle and may make cornering behavior up to perhaps "moderately hard" feel a little more linear. BUT . . . that requires that you retain the rubber bushings in the uppers and locate the PHB up around the UCA ear height on the pumpkin. You end up sacrificing a bit of resistance against wheel hop if that is a concern, and even the best PHB/C4L combination will eventually cause some tail-happiness if you corner it hard enough or abruptly enough (in severe cases, this can result in sudden snap-oversteer, as plenty of Fox-Mustang autocross drivers have learned).


Norm

 

[malibu43]

NORM,am surprise how much you know about this matter. i got very clear about the rc,my next race its in november, and i need some advice to where should be installed the ph.
i think the ph has to be installed in the driver side frame, and the other end about pumpkin height? its ok? .
Now am instaling my home made lower arm relocator(parallel to ground),its hard but i think it will be ready tomorrow.
other question, if i allready remove all the weight from the car ,from the rear ,should i need softer springs?,my thought was (less weight,less spring rate) am ok in the tought?
thanks very much
jorge pinto

 

[malibu43]

i forgot to say ,the i got the old upper control,with the stock bushings,.to run with a ph bard do i need to boxed them? am plainning to re install.
thanks