Will Sway bars alone help handling performance significantly w/o springs and shocks? I have 19" wheels on a coupe rear:275, front: 245

 

Yea, definitely.

 

Study the [multiple and varied] Tire Rack BMW/IS300 tests of incrementally adding stiffer bars and springs alone and both and the effects of 1" vs 1.5" drop springs.

Assuming a matched package, the springs about equalled the bars at 1.0-1.5% improvement per item............hard to exceed 3% improvement.

Lap times were only improved by 2%.

G forces increased a whopping [sic] 0.01G = 0.94>0.95G

http://www.tirerack.com/suspension/testing.jsp

Unfortunately things even remotely suitable for the street cannot improve MEASURED performance significantly. They can make the FEEL better especially to non expert drivers.........those that don't race for a living.

In my opinion sways are a much better deal especially adjustable ones.

Don't think I'm biased as I run Eibach springs and have for 8 years on my Q45 along with much stiffer rear bar [20mm+ springs = 130%>>>> 180%].

When a car comes equipt with a rear sway bar, the factory has already designed in a mild performance situation.......otherwise there would be no bar on the rear period..........the trick is to increase while maintaining WET SAFETY that the individual driver can control...........watch out for girlfriends borrowing the car in rain.

 

hmmm wet safety is very important, With my 19" wheels my ride height might seem higher and feels a lil' higher, what sway bar options would you suggest...

 

The most popular seems to be the Stillen, hotchkis are also good.

If you search you can find more info, and even vendors on this site selling them.

 

yes it will. but your next weakest link is going to be your tires, so you
might want to use the soft/med setting.

 

Please understand that sway bars of any size by their coupling action diminish the independent suspension [reduce independence].
Sway bars tend to reduce traction [while turning] by load shifting.

Therefore when you add sway bar stiffness, good idea to increase lateral stickson [sideways sliding] ability with wider tread contact patch........not necessary unless you increase bar stiffness by >50%.

Make sure the tire coefficient of friction curve vs temperature [wet and dry] is known to you, so you don't suddenly find yourself driving on glass when the temp drops or it starts to rain................requires some testing and accurate measurements.

The problem is that tires change with every day cycling so it is not a test once then forget........check tires every 5,000 miles for hardening of compound - use a Shore Durometer.

The closer you get to the ragged edge the more work it is to keep from going over it. Why the factory stays far away even in sporty sedans, they know typical owners won't maintain to new or change tires every 5,000 miles.

Careful about shocks by 60,000 miles most are half as stiff in rebound as brand new this dramatically speeds up body roll changes.

 

tire compound mandates over width for traction. ofcouse if you have
a wider tire of the same kind, it will adhere better if the alignment setting
is setup for whatever application that is.

just wanted to point that out since you're getting pretty detailed and
specific on your posts.

best thing is use the softest swaybar setting and drive through dry and
wet conditions with the traction control on. less activiation means you
can go stiffer on the setting. this is a safe way to setup your car.

 

OK, so Stillen sway bars, softest settings for rain with traction control on... got it.

Now, will it become a dangerous situation with HKS coilovers added to the equation?

 

When you add stiffer springs, the sway bars become a lesser part of the overall stiffness equation.

What counts is the roll stiffness ratio at the tire/road interface front and rear.

The published value of the springs tells little about this tire road interface value.