How weight bias effects sway bar sizing?

[Rusty G]

The weight bias on my car varies between 51/52 front and 49/48 rear.

The change is from full to empty tank. That's also with driver (it's rarely driver without one :D ) .

Most generic sway bar packages are within a 1/2 inch diameter of each other front to back.

Mine fall in that general area , being 36mm front/27mm rear.

My question is , since the car is very close to 50/50 , should my bars be similar in diameter?

Or should I try and get bars that mimics the exact weight bias (36mm front/34mm rear)?

I also have a 1 1/8 front bar (approx 28.5 mm), would the smaller front be a better match?

Last, the front bar is hollow, how does thgat effect it's "stiffness" compared to the solid rear bar?

Thanks in advance.

[David Pozzi]

Comparing diameters only works in a very very general way. You are correct that as front weight goes down, the front bar rate needs to go down, or rear bar rate has to rise to maintain balance. BUT you need to be looking at total roll resistance at the front and rear wheels, not bar diameters. The roll center heights need to be taken into account, as RCH (roll center height) affects how much cornering load is automatically resisted by the geometry, and this load does not go through the bars. A higher RCH requires a lower bar rate.

To do all this requires suspension software with all suspension geometry points front and rear mapped out, and vehicle center of gravity height and F/R location, data. Info on anti-roll bar dia, arm length and mounting, where it connects to the suspension or frame, spring rates and the spring ratio to the wheels, corner weights. The software assumes a fixed amount of tire grip front and rear, so if your rear tires are larger than the front, the answers the software give you will be skewed.

Most aftermarket bars are not so stiff that you should think of reducing rates. The Pro-Touring crowd usually has a lot of tire under the car and this increases cornering load applied, you usually need some pretty large bars to resist it. I would try a normal aftermarket bar setup, then add more rear bar if you have understeer. That's what we did on our 73 Camaro we autocross and open track.
David

[The WidowMaker]

Last, the front bar is hollow, how does thgat effect it's "stiffness" compared to the solid rear bar?


there are calculators out there, but a hollow bar is usually not that (20-30%) far off from a solid bar. it happens that way since a bars rate for say a 1.25" .25 wall bar is the rate of a 1.25" solid bar minus the .75" bar to make it hollow. my new bar is a 1.5 hollow, which is almost 40% greater in rate than a 1.25" solid. plus its lighter.

also, you must take into account the length of the bars arms. go to www.1speedway.com for a list of bar sizes, arm lengths and rates.

Tim

[Rusty G]

Thanks for the responces, hope you guys had a good holiday.

I am just looking for what works in a "very very general way".

The bars on the car are not a package, front is GM Fbody, rear is aftermarket.

I have a smaller front solid aftermarket 1 1/8 bar (vs fbody) so swapping it costs nothing but a few minutes of my time.

Here is a link to me introducing myself with specs included:

http://www.lateral-g.net/forums/showthread.php4?t=18152

As you see, not looking to out handle a Porsche but surprising them in a rusty wagon is fun.

I am thinking a upper balljoint spacer might be a good bang for buck mod.

They are availible in 1" and 2", thinking 1" might be the way to go on a daily driven vehicle.

Thoughts?