Hi all,

Quick question...been doing my research before ordering the H&R 19mm (planning on middle...maybe highest setting; we'll see). Perusing the motoring|underground forums, it was mentioned in one thread that a hollow 22mm swaybar was equivalent to a 19mm solid. I am mildly familiar with the diameter^4 formula, but I was curious as to whether it still applied to hollow pieces. I can't imagine it wouldn't apply, but I'd like to get a definitive answer from those who know more.

So, in short, is there a difference between hollow and solid swaybars, and if so, what is it?

Thanks,
Matt

 

I think it has more to do with wall thickness and material used. IE sells a 22mm hollow rear sway bar that they claim is equivilent to a 22mm solid bar. I can tell you that the thing is much stiffer that the stock one.

 

Where c is the inner diameter and d is the outer diameter, the stiffness
varies in proportion to d^4 - c^4, assuming they use the same kind of steel and
same proportions for both bars.

For example, compare a 19 mm solid bar to a 22 mm hollow bar with an
inner diameter of 18 mm (2 mm wall thickness).
19^4 = 130,321
22^4 - 18^4 = 234,256 - 104,976 = 129,280,
which is almost exactly the same in this case.
Pick a different wall thickness, however, and the numbers come out different.

The difference in weight, however, is proportional to the square of the diameters,
so the above mentioned 22 mm hollow bar weighs only 44% as much as the 19 mm solid bar
of the same stiffness.

 

Thanks for the quick responses...

I believe the H&R bar is a hollow piece. That being said, what is the effective resistance of the bar (i.e. what would it be equal to, if it is solid)?

- Matt

 

Is this the 22mm? I believe they state it is the same as a 19mm solid.

 

No, was looking at the 19mm here:

http://www.turnermotorsport.com/html...UCT_ID=71416-2

Around the boards here it seems to get the best marks. As has been mentioned, I'd like the car to turn in more from the middle than from the front (induce something closer to oversteer).

While it does not mention being hollow or solid and I can't provide a definitive link right now, I remember reading somewhere that the H&R was a hollow unit (again, 19mm is hollow).

Just looking for a correction unless I'm wrong, and if they are indeed hollow, what their effective size is.

- Matt

 

I believe the H&R are a solid bar. The H-Sports offer a hollow one http://www.h-sport.com/cgi-bin/EDCst...atalogno=22800 but I can't tell you the equivilent solid size.

 

Scottin, you're awesome.

I much prefer the solid unit, so thank you very much with the all explanations and so forth.

- Matt

 

I beleieve many if not all hollw bars are heat treated...this process affects stiffness.

 

True, although many solid bars may be heat treated as well.

 

I had the H&R solid bar and swaped it out for the H- Sport for the weight savings a couple of years ago. Still loving the H-Sport front and rear.

Randy
M7 Tuning

 

I've often wondered how to calculate hoe heat might affect swaybar operation, do you know? I can only assume knowing the alloy properties is key, but beyond that???

 

If you're going to calculate hoe heat, please be safe and wear a condom.

 

Stiffness is linearly proportional to Young's Modulus for the material selected.

Modulus of Elasticity (Young's Modulus)
A measure of the rigidity of metal. Ratio of stress, within proportional limit, to corresponding strain. Specifically, the modulus obtained in tension or compression is Young's modulus, stretch modulus or modulus of extensibility; the modulus obtained in torsion or shear is modulus of rigidity, shear modulus or modulus of torsion; the modulus covering the ratio of the mean normal stress to the change in volume per unit volume is the bulk modulus. The tangent modulus and secant modulus are not restricted within the proportional limit; the former is the slope of the stress-strain curve at a specified point; the latter is the slope of a line from the origin to a specified point on the stress-strain curve. Also called elastic modulus and coefficient of elasticity.


values for some alloys: (couldn't find a comparison of heat treated vs. non-
heat treated steels. Most have a value betwen 28 and 31 at room temperature.


http://www.engineeringtoolbox.com/yo...lus-d_773.html

 

Here we go...just had to google the right terms...a couple sources below say torsional stiffness is not affected
by heat treatment of steel:

http://pwatlas.mt.umist.ac.uk/intern...ted-steel.html

http://en.wikipedia.org/wiki/Carbon_steel

 

Nice

So the heat treating process hardens the metal in question, but doesn't make it stiffer - another condum reference

 

Well, someone gave their Strength of Materials book a workout this morning...

We were just having a discussion on hollow vs. solid rods earlier this week (torsional & axial forces) at work, had to break mine out to answer (quantitatively, not just anecdotally as is usually the case around there) some of the same questions.