Efini_7

iTrader: (1)

Is it ever a good idea under any circumstances to disconnect the rear sway bar in a FD for the track? I ask because i got coilovers several months ago and the spring rates are pretty high. I love the way they make the car feel overall, but the back end really likes to kick out with very little warning and it almost seems like it has less rear grip than before since it can't really lean over and 'take a set' through the turns. I've put the rear sway bar (a PFS adjustable sway bar) on the softest setting, and while that helped, i'd still like to feel a little more from the back end. I might end up with softer springs eventually (they're 11/9 f, r right now) but for now i was wondering how it would do if i just removed the rear sway bar sometime while i'm at the track between sessions. I just want to feel less like i'm drifting around the course...

Any thoughts?

Thanks.

Mahjik

iTrader: (1)

The guys at the track, that I knew, who ran the Ground Control Coilovers/Tokico setup always disconnected their rear sway bar.

artowar

iTrader: (1)

As long as you secure the ends up and out of the way, I don't see a problem.

Efini_7

iTrader: (1)

Yeah, i'd take the thing all the way off, probably.

Ok, just wanted to make sure it wouldn't seriously screw anything up.

If anyone else could chime in who's had some experience with this, that'd be great. Thanks for the current responses.

Mahjik

iTrader: (1)

Here's one of the cars I was referring to:

http://www.shutterfly.com/progal/album.jsp?pg=1

Pictures: DSC_4490.JPG, DSC_4491.JPG

Efini_7

iTrader: (1)

Link no workie.

Mahjik

iTrader: (1)

http://www.shutterfly.com/progal/alb...98cf62c88aca05

Page 2.

DamonB

You only have to disconnect one side of the bar to try it out. Trying never hurts.

Cheers!

As per the 1st post. Since the person was running coilovers (new springs and new shocks) he/she can select the rear roll stiffness via springs and via shock rebound and compression dampening.

The rear anti-roll bar or any roll bar should be the last thing that gets tuned on the suspension. It is the last chance solution to get the roll stiffnesses correct on the car.

fd_neal

iTrader: (4)

I wouldnt say the sway bar is the last chance solution. Sway bars will increase spring rates of the outside wheel while in a corner. They also change how the car transfers weight. The right bar needs to be used in conjunction with the rest of the setup so in that sense it might be the "last" mod. but i prefer to look at the whole setup as one mod...

With the right spring and bar setup youll be able to run a considerably softer softer suspension and achieve the same levels of grip (spring pushing the tire into the ground) Softer setups are generaly easier to drive, and thus faster in less experianced hands.

My personal thought is that if disconnecting the rear bar gets you the feel you want you should either look at a stiffer front bar or softer springs.

Efini_7

iTrader: (1)

I understand that it's not the "optimal" solution. I just wanted to make sure it was feasible and that the rear sway bar wasn't crucial to the suspension design of the car. Usually it's fine to remove it, but i just wanted to ask the question and double check anyways.

I would like to get softer springs in the future, but for now i'm gonna see how it feels w/o the rear bar. Front bar is already pretty stiff (PFS) as are front springs (600lb/in). Between those and the 500lb/in rear springs, i'm sure the body roll in the rear will be very manageable.

If i like it on the street i'll probably try it for my next event at the track. If it turns out that i don't like it than i'll work on the springs...but if i do, then yay!

Thanks for the replies.

Efini_7

iTrader: (1)

Hm. I makes me wonder if i could calculate the force applied to the outer wheel with stock springs and PFS rear sway bar vs. 500lb/in springs and no sway bar. I know that given they're the same, the softer spring setup would be better...but still...i'd be interested to know. Anyone have any formulas that could help me out? Anyone know exactly how much additional 'spring rate' a sway bar adds under cornering conditions? I'd love to discover the exact relationship between the two components...

DamonB

It's a simple figure but getting all the information beforehand to make the calculation can be a chore.

First you need to know the rate of the springs. Then you need to know the motion ratio of the suspension. With those in hand you can determine that an x amount of suspension movement equals a y amount of wheel rate and this will give you the roll spring rate assuming no bar at all and the car is cornering at steady state on a smooth surface.

Now you add a swaybar. First you need to know the rate of the bar and this is typically measured in pounds per degree of twist. Then you compute the motion ratio of the bar linkage so that an x amount of wheel movement equals a y degree of bar twist.

Now you can add the results of the springs and bar together and know that for x amount of suspension movement the bar adds y pounds of spring rate in roll.

Keep in mind there is still a limit. If the bar were infinitely stiff all that happens is that both sides of the suspension compress they're springs. The bar cannot create rate, it can only add more and more of the inside spring's rate until the bar is so stiff it collapses that spring as well. Make sense?

In truth you don't need to do all of that unless you're a nut or you're building a car I agree with Cheers! You pick springs to give the chassis the rates you desire and use the bars as a tuning tool to balance front vs rear weight transfer. Ideally the springs should do the work and there are limitations with what you can accomplish with bars only. My car is a perfect example with its soft stock springs. I run a big front bar to try and get roll stiffness in the car but it results in a much bigger compromise than stiffer springs would be.

DamonB

rate calculator for solid and hollow swaybars here:

http://www.auto-ware.com/updates/Aut...preadsheet.xls

Cheers!

Remember when are having problems with your car. Follow the old rule of thumb.
For the end that is giving you problems soften it.

Ie if it's understeering, soften the front, if it's oversteering soften the rear. That is true unless we can change the aero load on either end of the car.

Don't forget no matter how fancy your suspension geometries, roll bars or whatever are, the most important part of the car are the dampeners.

KevinK2

This is a "stiff, perpindicular arm" assumption formula, close enough for rear bar. Search for Puhn equations for bars shaped like the oem front.

In both cases, the lb/in resulting number is what I call the brick or bench rate. Brick rate being related to running over a brick at right or left wheel only, with no car roll. This rate assumes bar is on a test bench, one lever arm does not move relative to the pivots, and the other end is loaded, deflected, and the load/deflection is the official rate.

For getting effective rate at wheel as you described, for roll and weight transfer analysis, this basic bar "bench test" stiffness rate must be DOUBLED. I have verified this with my own beam calculations.

Say it benched at 1" deflection at one end that has 1000 lbs on it. In a corner with 1000 lbs at the links, one bar end is down 1/2", the other up 1/2". So in roll, the rate at the links is 1000/.5 = 2000 lbs/in. Use that number as a start, when figuring the reduced bar rate at the wheels.

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Efini_7: Based on testing with and without PFS rear, you could go back to stock rear as a tuning option. PFS now lists hollow bars .... I wonder if thay are the 32 and 19mm bars that eibach made but no longer sells. When were they purchased?

DamonB

Sure, but that's how bars are rated. Just as springs can have different installed values so can bars. We have to have a comparitive number to start at though and when installing on the same car the comparitive values between one bar and another or one spring and another are really what we're concerned about.

Efini_7

iTrader: (1)

Latest update:

I fiddled with the coilovers and readjusted the damper rates. I had forgotten where i had them set, so this really did make a noticeable difference. To begin with, the fronts were full stiff and the rears full soft. I did this because the stiffest setting on the front actually gave me the best ride on the street (no bouncy-bouncy) and i wanted the rears to be soft so it wouldn't oversteer so much. (I ran it this way on a skid pad a few weekends ago and it plowed like mad...which makes sense.) After re-adjusting it, i see how those settings really whacked out the handling overall. I softened the fronts to 4 (with 6 being the stiffest), and hardened the rears to 2 (were at 0). The car feels much more balanced overall and doesn't freak out in a fast sweeper like it used to. I'm going to ride like this for a while and see how i like it before changing anything else. I'll try and work on the dampers more and see how close i can get to the desired handling before messing with sway bars. I honestly didn't think the change in damper would affect the handling as much as it has. I thought i would have to mess with different springs to get what i wanted, thinking the current spring rates were to blame for the bad handling and that dampers couldn't really make up for it. But maybe they can do more than i thought...

Thanks for all the info, guys. I'll keep youi posted...

jpandes

Hmm, that's interesting. I never heard this before. I have both GC/Tokico's and on my way to first track day, my rear sway bar endlink broke. I actually heard it snap. I guess "somebody" was watching out for me.

DamonB

Shocks have no effect on skidpad numbers. The shocks only do anything when the pistons inside them are moving and with the car leaned over driving around in a steady state circle the shocks do zilch. If the piston in the shock isn't moving the shock isn't doing anything regardless of what the setting is.

The shocks have the biggest impact when the chassis experiences any sort of upset or transition. If the chassis is at steady state you're only feeling the springs and bars.

KevinK2

True for bar comparisons, even just a (Do^4 - Di^4) ratio is handy for comparing bar rates for a specific application.

But my point is when relating "bar rates" to spring rates, as you had mentioned, you have to avoid the common mistake made by 95% of internet suspension sites, that use the calculated bar rate as a basis that motion ratios are then applied to. This is like getting springs labeled 600 lb/in, when they are actually 1200 lb/in. Big difference.

Another thing to remember in suspension analysis is that lever arm (or motion) ratios must be squared when extrapolating rates out to the wheel.

maxcooper

I ran a track event with the rear bar disconnected on my car once. I just replaced the shock-bolt-end-link with a plain bolt on one side. It was a tight track and the car worked pretty well with that setup. It understeered, but you could use the throttle to steer. And the rear end was very controllable even when sliding it hard with the throttle.

Now I have a stiff front bar (Tri-Point w/0.188") and the stock (93 base) rear bar.

-Max

Efini_7

iTrader: (1)

^
That was actually my most recent thought. I'm really considering going with a stock rear sway bar, thinking that would be a good compromise. I'm going to go home and look at the stock schematics and see what kind of hardware i'd need to go back to the stock setup in the rear. (The PFS rear bar has custom bolts and fittings for each side.)