ryanater

iTrader: (2)

I have been hearing a lot about unsprung weight lately. I understand the basic principal. Anything that is not supported by the springs like an axle, wheels, brakes etc is unsprung.

I just don't understand why weight added below the springs affects your car more than weight added above the springs.

And why are swaybars unsprung weight? It seems to me that since the front is mounted to the subframe it wouldn't be unsprung.

Sam Strano

iTrader: (41)

Because sprung weight is controlled by springs, shocks, and swaybars. Unsprung weight is not, it's just hanging out with only the compression damping of the shocks able to do anything to help the way the mass clubs bumps. The heavier the unsprung weight the harder the car hits bumps and other impacts.

Basically it's just like when you wear heavy boots....

Only the rear bar is unsprung weight on this car (and not all cars). The front bar is sprung being bolted to the body. The rear is bolted to the axle.

ryanater

iTrader: (2)

Oh got it!!! So a hollow vs solid sway bar isn't a huge deal in the front but it's a lot more noticable in the back?

EchoMirage

iTrader: (3)

in terms of wheels/tires, think of it this way. would it be easier for you to pick up a 10lb bucket and swing it in a circle, or a 20lb bucket and do the same. same principle goes for the motor spinning heavier wheels vs. lighter ones.

and no.....a hollow rear bar isnt so much more noticable. youre talking a few pounds over the entire weight of a 3400+ lb car. thats like having a full tank of gas vs. half tank. do you really feel faster on a half tank then full?

Sam Strano

iTrader: (41)

The 5 pounds you save on the hollow rear bar is more noticeable than the 14 you save on a hollow front. Even if you don't notice, it matters. It like saying you are ok with 10 less hp because you really can't tell any difference....

I'd rather run a solid front/hollow rear than the other way around. But of course hollow at both ends saves the most mass. And fwiw, there are two ways to look at everything. Yes, the car is heavy so does shaving some mass here and there matter? On the other hand, the car is heavy and anything you can do to save mass helps. Unsprung mass is worth, in a suspension tuning/ride quality way a TON of normal weight.

Ever notice you are seeing more and more cars with aluminum control arms, carbon composite brakes and the like? That's to shave unsprung weight.

ryanater

iTrader: (2)

Ok well what about the strength of hollow bars compaired to solid bars or even chromemoly bars?

Or is a 35mm bar going to be just about the same no matter what it is?

ThumperNC24

iTrader: (1)

the solid bar will technically be stiffer, but not my much. I don't think chromoly makes much of a difference at all in sway bars

SS101

iTrader: (2)

tubular pieces work differently than rectangular pieces...tortional stiffness if a function mainly of radius (which is why driveshafts are hollow, there is no added benefit to having the middle filled with metal because it adds little stength compared to the outside of the shaft). stiffness in general is a funtion of affected area (read: area moment of intertia) which is why sway bars can be hollow; the hollow bars will deflect negligibly over the solid bar given the right wall thickness. i say negligible because the wieght savings are generally more significant then the small loss of sitffness. the downside is that hollow bars are more expensive. material composition, i.e. moly vs. mild steel, is somewhat of a moot point. moly is more brittle than mild steel and doesnt make many sway bar appearances because that's how a sway bar is going to fail, bending not shearing. brittle materials crack more than they bend (over simplified but it makes the point). that's how moly pieces are lighter than mild pieces, they use thinner walled tubing, but because making a sway bar stiff requires a given wall thickness, material choice among steels isnt very important...a mild bar will be almost exactly as stiff as a moly bar.

recap: hollow bars and solid bars of the same diameter are, for all intents and purposes, equally stiff. hollow bars cost more and weigh less, solid bars weigh more and cost less. as with so much in automotive modification, its a a balancing act.

...

if i'm totally off my nut, please let me know

madmo

iTrader: (2)

My moto save weight everwhere I can!

Sam Strano

iTrader: (41)

Solid bars are very slightly stiffer than a hollow bar (and the wall thickness matters on the hollow as well--I use a pretty thick front wall for hollow on my bars).

CM makes zero difference in how much roll stiffness the bar has. CM is not any lighter either, and in fact without proper heat treating CM is more brittle than mild steel which is not great since a bar has to flex doing it's job.

Ignoring fit, hardware, etc for all intents and purposed a solid bar of X size is very much the same as any other. But again that's ignoring fit, finish, and if you are buying a set what the other bar is to match.