Leonel

What is the weight difference between the solid and hollow torsion bars ?
is it worth it to spend the extra cash for the hollow version?Thanks

Skip

Difference is about five pounds each. The weight is not only lost from the car overall, but from a portion of the unsprung weight. Any loss in unsprng weight means crisper suspension response - this is the exact feedback we get... racers report a more precise feel and quicker response when compared to solid bars. Honestly, this would only be noticable by those very familiar with the handling of their car. Hopefully one of the members here will give you more first-hand information.

Good Luck!

Autoenthusiast

How are torsion bars unsprung? They're in the torsion bar tube that's mounted to the chassis which is sprung.

Skip

The weight of the spring (torsion bar in this case) is approximately 1/2 of each weight, sprung and unsprung. It is the spring itself that defines the transition from sprung to unsprung weight - as it is the measurement of how much mass is applied to each. Another realistic example relating to the 944 is the front seemingly progressive sport springs - there is a heavy and light end to them... though they are designed to fit either way, based strictly on performance they should be installed with the heavy end on top (additive to the sprung weight) even though they were designed to run the other way, and are marked as such.

Skip

Leonel

is the spring rate different between the solid and hollow bars of the same size ?

Autoenthusiast

Skip:
I see what you mean that it's sort of unsprung but I don't think it would make a difference:

The weight of the coil spring makes perfect sense since you want the least possible weight travelling with the wheels and the bottom part of the spring clearly travels as much as the wheel and the amount of travel decreases as one goes up the spring towards the top. I'm with you to here.

The torsion bars, on the other hand, only twist when the suspension is compressed but there is little in the way of travel. I have a hard time believing that the inertia of a 3cm bar at the axis of rotation makes a measureable difference, especially the center which has the least distance of any part in the setup to move. The intertia of this part should be negligable in the scope of the entire trailing arm moving since the torsion bar is the axis of rotation.

I suppose though...if you're fabricating suspension parts to be lighter and painting a car white because it's the lightest color any improvement is worthwhile.

I don't mean to be disagreeable but if I'm missing something about how torsion bars work I'd like to figure it out.

btw: How do trailing arm setups compare to wishbone suspensions in high performance applications? I only ask because I remember that porsche has moved away from trailing arms in the later cars (right?).

Manning

Yeah, I'm kind of wonder the same thing. I am leaning more toward Autoenthusiast's thinking on this.

Skip

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Leonel:
<strong>is the spring rate different between the solid and hollow bars of the same size ?</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">Torsion bars (and sway bars) are normally quoted using the effective diameter, not the actual diameter. Depending on construction, a hollow bar may be larger or smaller than the equivalent and standard solid bar.

S

Skip

</font><blockquote><font size="1" face="Verdana,Tahoma,Helvetica">quote:</font><hr /><font size="2" face="Verdana,Tahoma,Helvetica">Originally posted by Autoenthusiast:
<strong>Skip:
I see what you mean that it's sort of unsprung but I don't think it would make a difference..</strong></font><hr /></blockquote><font size="2" face="Verdana,Tahoma,Helvetica">How about "not much of a difference" <img border="0" title="" alt="[Wink]" src="wink.gif" /> The mass of the unsprung and sprung weight added total have to equal the overall weight of the vehicle. The spring has to move the unsprung mass back to its loaded position (relative to sprung weight, the spring actually attempts to return to null or unload). The mass of the unsprung weight is anything the spring has to push back toward the naturally loaded position). Because the spring (torsion bar) is mouted inside of a tube (sprung weight) that is mounted to the chassis (sprung weight), the total weight of 1/2 the spring is not suspended in a normal sense as it is with a coil spring or leaf spring. However, the mass of the unsprung portion of the spring still has to fight itself to return to null (or naturally loaded). The same basic priciple can be applied to other parts of the rear suspension such as the drive axle and the trailing blade... while they are anchored to a fixed point on one end, their mass is also added partly to the overall unsprung weight. At least, that's what my wife tells me... <img border="0" title="" alt="[Wink]" src="wink.gif" />

S

Leonel

now,how will these hollow bars hold up on a DD?

Autoenthusiast

lol...nice justification. I'm happy with "not much of a difference." I'm sure it's worth it to someone...I've just got to worry about driving well enough to notice the difference for now.

BTW, I didn't realize that you were with paragon products...I buy parts from you whenever possible. Thanks for the excellent customer service & pricing!

Skip

DD?

Leonel

Daily Driver

Skip

Double Damn - shoulda known that one <img border="0" title="" alt="[Wink]" src="wink.gif" />

Daily driver would not benefit from the hollow sway bars. However, the hollow bars are every bit as durable as the solid bars - they would "hold up" fine (nice choice of words )

S